A FUNDAMENTAL STUDY ON CURRENT INDUSTRIAL LIGHTING SYSTEMS

AND ANALYSES OF RETROFIT OPTIONS

by

MATTHEW BLAIR CLINTON

A THESIS

Submitted in partial fulfillment of the requirements for the degree of Master of Science in the Department of Mechanical Engineering

in the Graduate School of The University of Alabama

TUSCALOOSA, ALABAMA

2008

Copyright Matthew Blair Clinton 2008

ALL RIGHTS RESERVED

v

CONTENTS

ACKNOWLEDGEMENTS ............................................................................................... iii

LIST OF TABLES ............................................................................................................ vii

LIST OF FIGURES ......................................................................................................... viii

ABSTRACT ........................................................................................................................ x

CHAPTER 1: INTRODUCTION ...................................................................................... 1

CHAPTER 2: HIGH-INTENSITY DISCHARGE LAMPS .............................................. 5

2.1 HID Lamp Construction ....................................................................................... 6

2.2 HID Ballasts ........................................................................................................ 11

2.3 HID Evaluating Criteria ...................................................................................... 12

2.4 HID Technological Advancements ..................................................................... 16

CHAPTER 3: LINEAR FLUORESCENT LAMPS ........................................................ 29

3.1 Linear Fluorescent Lamp Construction .............................................................. 29

3.2 Linear Fluorescent Lamps Types ........................................................................ 33

3.3 Fluorescent Ballasts ............................................................................................ 38

CHAPTER 4: FUTURE ALTERNATIVES .................................................................... 43

4.1 Induction Lighting .............................................................................................. 43

4.2 Light-Emitting Diodes ........................................................................................ 45

CHAPTER 5: LIGHTING CONTROLS ......................................................................... 49

5.1 Occupancy Sensors ............................................................................................. 49

5.2 Photocells ............................................................................................................ 53

5

CHAPTER 2

HIGH-INTENSITY DISCHARGE LAMPS

High intensity discharge lamps are commonly used in both high- and low-bay

applications to provide, powerful, efficient, high-quality light. Suffice it to say, HID

lamps have long been the standard for industrial facilities, and continue to be the lighting

workhorse for the illumination of manufacturing plants around the country. Their

compact design, attractive color characteristics, and high lumen efficacy make HID

lamps an appealing option for industry applications.

Three primary lamp types comprise the family of industrial HID lamps. These

lamp types include mercury vapor, high-pressure sodium, and metal halide. Each lamp

utilizes a unique set of materials, namely metals, to produce light, but all three adhere to a

common form of operation. Table 1 compares each lamp according to several features

[2]. Mercury vapor lamps will not be discussed because they have long become obsolete

and, for the most part, are not used in manufacturing facilities.

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Table 1. HID Lamp Comparison

HID Lamp Comparison

Features Mercury Probe Metal Halide High Pressure Sodium

Color White White Yellow

Efficacy (L/W) 50 60 – 85 100 – 125

Lumen Maintenance 50% 65% 90%

Lamp Wattages 50 – 1000 175 – 1000 35 – 1000

Lamp Life (kHrs) 24+ 6 – 20 24+

Source: Taken from Ref. 2. 2.1 HID Lamp Construction

There are two main parts to a HID lamp: an outer bulb, and an arc tube. Light is

formed in all HID lamps through the discharge of an electric arc inside the arc tube.

Contained inside the arc tube are two tungsten electrodes, a starting gas, and arc metal.

The starting gas, either argon xenon, or a mixture of neon, argon and xenon, will

facilitate starting the lamp at low pressure and ambient temperatures [1]. The arc metal

consists of metals and halide components of metals. An electric field is passed between

the starting electrode and the main electrode which allows the starting gas to volatize the

arc metal. The subsequent decrease in resistance between the main electrodes caused by

the volatized arc metal creates an arc in the tube [1]. As the arc metal evaporates into the

arc discharge, different metals will release distinct lines of radiant energy [1]. Because of

this, each type of HID lamp produces light characteristic of the metals contained in the

arc.

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The outer bulb, made of either a soft or hard glass, encompasses the arc tube,

providing it protection from the environment. The outer tube also functions to filter out

unnatural light and short wavelength ultraviolet energy, absorbing a majority of the

unwanted radiation while allowing the visible light to pass through [1]. The inside of this

outer bulb can also be coated with a diffusing material to reduce brightness or a layer of

phosphors which absorbs the UV radiation to improve color-rendering properties.

Between the arc tube and the outer bulb, a low-pressure gas or vacuum is present. Fig. 1

depicts the basic structure of an HID lamp [21].

Fig. 1. A basic HID lamp [Taken from Ref. 21].

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2.1.1 Metal Halide

Metal halide lamps were initially created in the 1960’s for use in industrial

settings to provide a compact, efficient, and intense source of light [1]. They have now

replaced the much outdated mercury vapor lamp, and are available in a wide array of

sizes and configurations to meet the varying demands present in commercial, residential,

and industrial applications. They are commonly referred to as a “point” source of light,

operating under high temperature and pressure. Because of the blue light they emit,

metal halide lamps are often the most ideal option for providing a primary source of light

in situations where no natural light is available. Most manufacturers offer metal halide

lamps in low, mid-range, and high wattages. Metal halides are most commonly seen in

wattages of: 175-W, 200-W, 225-W, 300-W, 320-W, 350-W, 360-W, and 400-W [1].

A metal halide lamp is constructed in a similar manner to its predecessor, the

mercury vapor lamp, but boasts some significant improvements. Where light is produced

through the vaporization of mercury in a mercury vapor lamp, a process that continues

until the amount of mercury contained in the arc tube is completely vaporized and

depleted, a metal halide lamp utilizes a regenerative cycle to maintain light output [1]. In

a metal halide lamp, a compact arc tube contains a mixture of gases, commonly a high-

pressure mixture of argon, mercury and a variety of metal halides. As voltage is applied

to the electrodes and an arc is formed, the argon gas is easily ionized, sustaining the arc

and producing intense heat to vaporize the mercury and metal halides contained within

the tube. As the temperature and pressure increase inside the tube, and the halide vapors

converge on the intense central core of the discharge, the halides separate from the metals

allowing the metals to produce a bluish-white light. After the metal atoms have radiated

9

their spectrum, they return to the cooler arc tube wall to recombine with halogen atoms,

repeating the cycle [1]. Fig. 2, depicting normal metal halide lamp construction, is

displayed below [1].

Fig. 2. Metal halide lamp construction [Taken from Ref. 1].

2.1.2 High-pressure Sodium

High-pressure sodium lamps are one of the most efficacious light sources

available, with the ability to attain efficacies of nearly 150 lumens per watt. They are

commonly used outdoors because of their unmatched efficacy, long life, and poor color

rendition. In industrial applications they are most often seen in warehouses or low task

areas where minimal color contrast is sufficient.

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The production of light in a sodium lamp is achieved when an electric current is

passed through sodium vapor [1]. In a typical high-pressure sodium lamp there exists an

arc tube, inside which an amalgam of metallic sodium and mercury resides to produce

light through vaporization, and a small amount of xenon functions as a starting gas. The

arc tube is made of a refractory material, namely aluminum oxide (alumina), to resist the

corrosive effects of the high-temperature sodium [1]. The outer envelope is typically

evacuated to isolate internal electrical components from environmental effects and

maintain a steady arc temperature.

While low-pressure sodium lamps typically radiate energy in the principal double

D lines of sodium at 589nm, the high-pressure sodium bulb will radiate energy across the

visible spectrum because of the pressure broadening associated with higher sodium

pressures in the lamp [1]. The resultant light output is no longer monochromatic, making

colors distinguishable and thus more suitable for indoor applications. Another important

feature inherent to the sodium lamp is the absence of a starting electrode and the presence

of an ignitor, which provides a high voltage, high frequency pulse to start the lamp. The

current application of this feature in pulse-start metal halide bulbs has seen

groundbreaking results. Fig. 3 displays the typical construction of a high-pressure

sodium lamp [1].

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Fig. 3. High-pressure sodium lamp construction [Taken from Ref. 1].

2.2 HID Ballasts

A HID lamp must also have a ballast in order to operate effectively. Because the

light source does not regulate its own current consumption well enough, it must utilize

the services of a ballast to perform this operation. All HID and fluorescent lamps present

a negative resistance to the power supply when connected in an electrical circuit. If the

ballast were not used to provide a positive resistance in the circuit, the lamp would draw

an increasing amount of current until it failed or destroyed the power supply. Ballasts

have the reputation of being fairly intricate devices even though their operation is quite

simple.

Ballast types are numerous, but there are two categories for establishing their

function: magnetic or electronic. Magnetic ballasts are similar to transformers in that

they use an inductive core and coil to slow down changes in current. An inherent

annoyance with magnetic ballasts is their tendency to produce a flicker because of their

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low frequency modulation. They also vibrate which causes a noticeable hum. Electronic

ballasts use solid state electronic circuitry to produce starting and operating currents for

the lamp. They are favored over magnetic ballasts because of their ability to take the

frequency of power flowing from the mains (50 or 60 Hz) and transform it to 20,000 Hz

or more [1]. This eliminates the stroboscopic effect (flicker) and constant humming

prevalent in the operation of magnetic ballasts. In addition, electronic ballasts offer

higher system efficacy because of efficiency gains in the ballast itself, such as the use of

a capacitor for lower line losses over an inductor [1].

2.3 HID Evaluating Criteria

There are several basic criteria upon which the two lamp types can be

distinguished for their performance in those areas. Some of those criteria will be used to

discuss the performance of both lamps.

2.3.1 Lamp Warm-up and Re-strike Times

An important aspect of any light source is its ability to yield light quickly. An

attractive light source will reach its full output of light and maintain its normal operating

color in the shortest amount of time, whether that be from first start or hot start (re-

strike).

2.3.1.1 Metal Halide

Although metal halide lamps below 150-W use ignitors, which provide enough

voltage across the main electrodes to start the lamp, most metal halide lamps above 150-

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W in operation today use a standard starting probe which is part of the lamp circuit. It

takes time for the metal halides in the arc tube to warm up and evaporate into the arc; the

time it takes a lamp to reach 90% of full light output (warm-up) can vary between 2 and

15 minutes. Re-strike times are generally a lot longer because it takes a while for the

traditional pinched-body arc tube to cool down. In order to reignite, the temperature and

vapor pressure inside the arc tube must reach a reasonable level; otherwise, the high

required starting voltage cannot be applied without destroying the lamp. Re-strike times

for metal halide lamps typically vary between 5 and 20 minutes. Pulse start systems,

which utilize an ignitor have superior warm- up and re-strike times over standard probe-

start systems [22]. Fig. 4, taken from the National Lighting Product Information Program

(NLPIP), illustrates this point [22].

Fig. 4. Warm-up and re-strike comparison for probe-start and pulse-start lamps [Taken from Ref. 22].

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2.3.1.2 High-pressure Sodium

To start a high pressure sodium lamp, an ignitor has always been used for creating

a high voltage, high frequency pulse. Generally, the vapor pressure is lower and the

starting gas is ionized more easily with this configuration than it is with convention probe

start metal halide lamps. The arc is, therefore, created faster, allowing for shorter starting

times, and consequently, warm-up times. Re-strike times are also shorter because of a

lower vapor pressure and the presence of an ignitor.

2.3.2 Lamp Life and Lumen Maintenance

The benefits from long lamp life are glaringly obvious. A lamp that lasts longer

will save money in replacement and maintenance costs. The average rated life, which is

provided by most manufacturers, is determined when 50% of a group of lamps initially

installed during a test are still operating. “The procedure prescribes operating cycles for

HID lamps of 11 h on, 1 h off” [1]. However, lamp life listed by manufacturers is

generally based on run times of both 3 and 12 hours. Factors affecting lamp life include

but are not limited to: burn position (vertical or horizontal), number of starts, high or low

operating voltage, ineffective control devices (ballasts, capacitors, etc.), and extremely

high operating temperatures.

Lumen output for lamps is normally tested by the manufacturer and measured

after 100 hours of operation (initial lumens) and at 40% of rated lamp life (mean lumens)

[1]. A lamp that maintains its initial lumen output throughout the course of its life would

certainly be ideal. However, this is only ideal, for lamps will lose lumen output gradually

over the course of their life. Fortunately, most causes of lumen depreciation can be

15

corrected and have been as technology has improved. Lumen maintenance curves for

three 400-W HID sources are displayed below in Fig. 5 [1].

Fig. 5. Lumen maintenance curves for 400-W HID light sources [Taken from Ref. 1]. 2.3.2.1 Metal Halide

Of all HID lamps, metal halide lamps tend to experience a greater level of lumen

depreciation. Also because the electrodes used in metal halide lamps evaporate more

readily, they experience shorter life cycles. Toward the end of their life (the last 40%),

metal halide lamps can experience significant color shift. In color critical situations

where the color shift might be objectionable, the lamp will be replaced. Standard metal

halide lamps generally last from 10,000 to 20,000 hours [1].

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2.3.2.2 High-pressure Sodium

High-pressure sodium lamps utilize smaller diameter arc tubes and an electrode

construction similar to that of mercury lamps. The electrodes contain metal oxides

embedded within the tungsten coil which allow for a slower evaporation process. This

slow evaporation process means less “sputtering” over the course of the lamp’s life

yielding higher lumen maintenance values than those present in typical metal halide

lamps [1].

“The life of a high pressure sodium lamp is limited by a slow rise in operating

voltage that occurs over the life of the lamp” [1]. This slow rise in voltage is caused by a

chain of events that cause termination of the lamp when the ballast can no longer supply a

high enough voltage to reignite the arc. The typical lifetime of a high pressure sodium

lamp is 16,000 to 24,000 hours [1].

2.4 HID Technological Advancements

Ever since both metal halide and high pressure sodium lamps were developed in

the 1960s to improve the operational shortcomings of mercury vapor lamps, there has

always existed a tradeoff between both lamps which inherently limited their versatility.

For decades high-pressure sodium lamps have been used as the energy saving alternative

to metal halide lamps. More specifically, they were considered the most viable choice

“when color quality is secondary to low operating and maintenance costs” [2]. In

manufacturing facilities, the characteristic yellow light produced by high-pressure lamps

is normally reserved for outdoor applications and color-indifferent areas where low

contrast light (poor color rendition) is tolerable, as is common in most warehouses and

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storage areas. However, when higher quality white light is necessary, as is the case in

providing light for the surfaces in most industrial facilities, metal halide lamps were

chosen because they distribute crisp, white light with higher color rendition. For

specifiers and plant managers alike, it was always a choice between a source with good

color quality and a source with good operational efficiency; no single lamp presented

both merits.

2.4.1 Metal Halide

This dilemma in HID lighting existed for decades. While standard metal halide

lamps are still keeping most manufacturing facility floors lit, and high-pressure sodium

lamps maintain a relegated role in providing light to secluded areas which see little

occupation, revolutionary research and development is devoted to changing this scenario.

Within the last 10 years considerable research has led to significant innovations in the

development of metal halide lamps allowing them greater versatility. The metal halide

lamp was chosen because “of all the lamps in the high-intensity discharge (HID) family,

the metal halide family of lamps has the brightest future” [3]. Despite their limitations,

metal halides already offer much better light quality than mercury or sodium lamps and

have a potential for modification which far outweighs other lamps in the HID family.

Because they could already produce the coveted white light demanded by the industrial

sector, they were an obvious choice over mercury and high-pressure sodium lamps for

future development.

A company on the forefront of integrated luminaire technology, focused solely on

providing new metal halide lamp and ballast systems, Venture Lighting, strives “to be the

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best metal halide lamp company in the world and to dominate in the development of

metal halide lamps for general lighting” [23]. Heralded as “the fastest growing metal

halide company in the world,” Venture Lighting is the only corporation concentrated on

this technology [23]. Presently the owner of many design patents on pulse-start lamps

and ballasts, they are providing the lighting industry with many innovative options,

rectifying the problems plaguing the old standard probe-start lamps. Another company

dedicated to solving this paralyzing dilemma in HID lighting, Advance, often considered

the industry leader in the manufacturing of new ballasts, is regarded as the top source for

innovations and designs in fluorescent, HID, and LED ballasts in North America.

Leading an aggressive pursuit of this desirable integrated systems approach to solving

key operational limitations of HID lighting, Advance coordinated a revolutionary

cooperative effort between itself and the top four U.S. lamp manufacturers to coalesce

issues facing the formerly distinct lamp and ballast industries. Lamps and ballasts had

always been seen prior as separate entities in the design process, which Advance

recognized as an impediment to the process needed to solve this dilemma. Advance has

performed substantial research in conjunction with these lamp manufacturers to

overcome many design flaws in probe-start metal halide lamps. Both of these sources

will be documented as references for most of the changes in metal halide lamp design and

operation.

2.4.1.1 Pulse-start Technology

The quest of Advance, and Venture Lighting alike, was a complete systems

approach to solving the major dilemma in HID lighting. Metal halide lamps must be

19

considered a complete system, more than any other lamp [3]. All key components

(ballast, ignitor, controls, lamp and fixture) must work together to get the best

performance [3]. Because almost every lamp is designed individually and is different

chemically, containing different doses of chemicals, careful attention must be paid in

designing the whole system. Thus, it was essential that the problem be tackled in this

manner.

The problem with probe-start technology surfaced when lamp manufacturers

began to focus on improving performance features in metal halide lamps, specifically

lumen efficacy and lamp life. In order to reach this end, manufacturers desired greater

fill pressures and different chemistries inside the arc tube; however, the benefits of these

improvements inside the arc tube could not be realized unless a modification was made to

allow for higher starting voltages. Probe start systems, which only allowed for 600-volt

peak starting voltages, could not accommodate the arc tube changes. In other words, to

see an increase in lumen efficacy and lamp life, a higher starting voltage would need to

be applied to the lamp, which the standard probe-start system was incapable of doing.

That is when researchers seized the opportunity to apply present technology to a different

lamp type. By using an ignitor, the integral device already used in high-pressure sodium

lamp circuits to apply starting voltages, manufacturers were able to revolutionize the way

metal halide lamps operate.

Pulse start technology has existed in metal halide lamps in the 150-W range and

smaller for quite some time, yet within the last five years manufacturers have started

applying the technology to a broader range of lamp sizes. At first glance, the difference

in a standard probe start lamp and the modified pulse start lamp seems minor, yet the

20

consequent gains in overall lamp operation are vast. A conventional metal halide system

consists of a lamp and probe start ballast. Inside the arc tube are three electrodes, “a

starting probe electrode and two operating electrodes” [22]. The ballast applies a high

starting voltage to the probe, normally greater than the voltage applied to the main

electrodes during operation, creating a discharge in the small gap between the probe and

one of the main electrodes. “Electrons then jump across the arc tube to the other

operating electrode to help start the lamp” [22]. Once the main arc is established and the

pressure and temperature begin to rise in the arc tube, the probe electrode is removed

from the circuit by a bi-metal switch. A pulse-start system does not use a starter

electrode. Instead, an ignitor sends a series of high voltage pulses (usually 3 to 5

kilovolts) across the two main electrodes [22]. It is important to recognize that the ignitor

is an integrated part of the ballast. Therefore, pulse-start lamps will not operate on

traditional probe-start ballasts.

By eliminating the probe to start the lamp, a level of performance from metal

halide lamps that never existed before is made possible. Because the probe is no longer

present inside the arc tube, “the amount of pinch (or seal) area at the end of the arc tube is

reduced, which results in a reduced heat loss” [22]. This distinction opened up a wealth

of opportunities, allowing manufacturers the flexibility to optimally reshape arc tubes and

increase fill pressures and temperatures inside, producing greater light output (arc tube

modifications are discussed below). Additionally, two of the key elements prone to cause

premature lamp failure, the bi-metal switch and probe electrode, are removed from the

circuit in a pulse start lamp, boosting lamp life to levels only attained previously by high-

pressure sodium lamps. Furthermore, the series of pulses heat up the lamp faster during

21

starting, creating better warm-up times. Finally, probably the most distinguishable

feature in the pulse-start lamp is a reduction of tungsten sputtering, an undesirable

characteristic in probe-start lamps which caused considerable lumen depreciation as

tungsten blackened the arc tube wall as a lamp aged [22].

Fig. 6 displays the subtle difference in probe-start and pulse-start lamps which

produces so many gains in performance [22]. The probe electrode and bi-metal switch

are easily visible in the figure.

Fig. 6. Construction of probe-start vs. pulse-start lamps [Taken from Ref. 22].

Manufacturers claim many achievements for pulse-start systems over their

predecessor. The following list of improvements obtained from Advance and NLPIP

yields many of these performance achievements [2, 22]:

• Depending on lamp wattage and burning cycle, longer lamp life of up to 50%

over traditional probe-start metal halide lamps (20,000 – 30,000 hrs)

• Better lumen maintenance – increases by up to 33% in most lamps

22

• Greater efficacy – lumen output per watt increases by 25% to 50%

• Superior color rendition – a 30% improvement of up to 85 CRI

• Reduced color shift and improved lamp to lamp color consistency

• Faster warm up and re-strike times – warm up time is often cut in half to 2

minutes and re-strike hovers around 3 to 4 minutes

• Better cold starting capability – start at temperatures as low as -40°C (-40°F)

Table 2 yields a simple comparison of probe-start and pulse-start metal halide lamps

to high-pressure sodium lamps [2]. The gap in performance between probe-start metal

halide lamps and high-pressure sodium lamps is evident from these criteria.

Table 2. Standard HID Comparison with Pulse-start Metal Halide

Comparison with Pulse Start Metal Halide

Features Probe Metal Halide Pulse Metal Halide High Pressure Sodium

Color White Whiter Yellow

Efficacy (L/W) 60 – 85 90 – 110 100 – 125

Lumen Maintenance 65% 70% - 75% 90%

Lamp Wattages 175 – 1000 35 – 1000 35 – 1000

Lamp Life (kHrs) 6 – 20 10 – 30 24+

Source: Taken from Ref. 2. 2.4.1.2 Arc Tube Improvements

A direct consequence of the elimination of both the probe electrode and bi-metal

switch in pulse-start metal halide systems allowed for some major innovations in arc tube

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design. Venture Lighting has patented and crafted an arc tube design which reshapes the

arc chamber to provide a contoured fit of the arc itself. This unique quartz sculpting

process, resulting in Venture Lighting’s patented Uni-Form body, eliminates the pinched-

seal design which prevailed for nearly 30 years in the industry [23]. Fig. 7 displays this

contoured Uni-Form body arc tube in comparison to the pinched-seal design [23]. Not

only is the arc tube smaller and lighter, allowing it to heat and cool at speeds faster than

the previous pinched seal design would allow (better warm up and re-strike times), but it

creates a uniform geometry which produces uniform heating of the metal halides in the

arc tube. This allows the materials in the arc tube to reach a higher average temperature.

Higher temperatures equate to a higher light output from the arc tube. Venture Lighting

claims many performance improvements in their pulse-start systems because of the

formed-body arc tube, namely: higher efficacy, better color uniformity, faster warm up

and hot re-strike, and longer life [23]. Fig. 8 displays formed-body arc tubes inside two

different shaped metal halide lamps [27].

Fig. 7. Common metal halide arc tubes [Taken from Ref. 23].

24

Fig. 8. Formed-body arc tube inside two differently shaped metal halide lamps [Taken from Ref. 27].

An additional finding, which was the result of a tinkering similar to that of the

installation of an ignitor in the metal halide ballast, came “when Phillips engineers

borrowed a ceramic arc tube from a sodium lamp and stuck it into a metal halide lamp”

[3]. Manufacturers soon discovered a superior improvement in color performance. This

improvement in color offers CRI values in the 80 to 90 range, approaching that of

halogen lamps. Possibly the most important consequence of this discovery is the almost

guarantee of complete color consistency (meaning no color shift during a lamp’s

lifetime). Lumen maintenance also improves in ceramic metal halide lamps. Though

ceramic metal halide lamps are essentially a perfect match for retail and residential accent

25

and downlighting applications because of their ability to replace halogen and

incandescent lamps, they are great for color-critical spaces often prevalent in industrial

facilities.

2.4.1.3 Electronic Ballasts

Traditionally, metal halide lamps have operated on a magnetic ballast, consisting

of a core and coil which are relatively heavy, hot (when operating), and bulky. Many

ballast manufacturers now offer electronic ballasts that are smaller, lighter, and provide

better performance [3]. Electronic ballasts have been successfully used with fluorescent

lamps for years mainly because of reduced energy losses and dimming capabilities, but

only recently have they taken flight in high-wattage HID applications. Electronic ballasts

use solid state circuitry to control voltages and currents for starting and operating the

lamp in a manner more efficient than magnetic ballasts. In other words, they generally

accomplish the task of current regulation with a lower input wattage to the system than

do their predecessors. They also have the ability to operate at higher frequencies, often

reaching 100 kHz and above. Higher frequency operation of ballasts reduces tungsten

electrode sputtering, and therefore consequent deposition on the arc tube wall. This

improves many facets of a lamp’s performance including: lumen maintenance, lamp life,

warm up and restrike, and color stability. All electronic ballasts use pulse starting and

therefore gain additional operational efficiencies from the use of an ignitor (as mentioned

previously pulse starting also reduces tungsten sputtering). Another appealing advantage

of electronic ballasts is their ability to allow lower dimming levels at higher efficiencies

than magnetic ballasts could attain. Conventional magnetic ballasts can only attain

26

dimming levels of 40% to 50% of full output, with significant reductions in system

efficiency [3]. Electronic ballasts can drop lighting levels lower while still maintaining

relatively good system efficiencies. The combination of these features of electronic

ballasts and the potential to apply ceramic arc tubes to metal halide lamps has produced a

viable alternative source for many retail applications. The future for electronic ballasts in

the industrial sector is somewhat uncertain because owners are hesitant to use them at

such a high initial cost. Presently, it is difficult to consider a major capital project for

replacing old magnetic ballasts on metal halide lamps because of high initial costs, but

recent trends show that the price of electronic ballasts is decreasing.

Fig. 9 is a photograph of Advance’s Dynavision electronic HID ballast. These

ballasts operate with 320-W and 400-W HID lamps. An innovative microprocessor-

based design offers significant increases in lumen maintenance with continuous dimming

of the lamp.

Fig. 9. Advance’s Dynavision electronic HID ballast [Taken from Ref. 28].

27

The following is a list of advantages provided by electronic HID ballasts [13]:

• Improved light color and output

• Thirty percent longer lamp life and lower lumen depreciation

• Continuous dimming capabilities

• Reduced energy costs

• Smaller size and lighter weight

• Silent operation

• Flicker-free

• High-power factor (0.99) and low harmonic distortion

2.4.2 High-pressure Sodium

Because metal halide lamps were essentially the “chosen” HID lamp for future

development, not much has been done to improve the performance of high-pressure

sodium lamps. Several manufacturers like Phillips, GE, and Venture Lighting offer high-

pressure sodium lamps with better color rendition, but these retrofit options still provide

warmer color temperatures (2,200K) and a shorter life (15,000hrs). These options are

attractive because they yield better quality light with a simple lamp retrofit, but they will

never offer the benefits afforded metal halide lamps due to lack of new technology (see

aforementioned section on metal halide advancements). Fig. 10 displays a high-pressure

sodium retrofit option with improved color rendition manufactured by Phillips.

28

Fig. 10. Phillips Ceramalux® high-pressure sodium lamp [Taken from Ref. 29].

The characteristic yellow light provided by high-pressure sodium lamps is more

than just a limiting factor for development; it seems it has become responsible for their

demise. As the production of metal halide lamps with increasingly better efficacies and

lumen maintenance values continues, high-pressure sodium lamps will most likely be

utilized for fewer applications and eventually bumped from the market. Applications

where the unwanted yellow light source is chosen for reasons of efficacy and lumen

maintenance are diminishing. Metal halide lamp manufacturers are creating new lamps

with all the color benefits of previous sources and performance qualities approaching

those of high-pressure sodium lamps. Additionally, people are beginning to prefer higher

quality white light for outdoor and other niche applications controlled by high pressure

sodium lighting because of these advances in metal halide lamps. The T-12 fluorescent

lamp has been dealt similar circumstances. It presently dominates the fluorescent market

much like high-pressure sodium lamps still dominate their niche applications, but both

are fast approaching the end of their useful lives because of more efficient and better

quality alternatives.

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CHAPTER 3

LINEAR FLUORESCENT LAMPS

Fluorescent lamps are manufactured in a variety of shapes and sizes. Linear

fluorescent lamps represent a distinct family of straight-tube light sources that generate

light through the excitation of mercury atoms and subsequent fluorescence of a phosphor

coating. Three particular types of linear fluorescent lamps will be described in

anticipation of the analyses that follow.

3.1 Linear Fluorescent Lamp Construction

In 1857, a French physicist named Alexandre E. Becquerel began experimenting

with the luminescence of substances when placed in a Geissler tube. These discoveries

would lead to theorizations about the construction of fluorescent tubes similar to those

seen today. Heinrich Geissler, a German glassblower, had earlier created a mercury

vacuum pump capable of inducing a vacuum in a glass tube to a level not previously

attainable. When current was passed through this tube, a green glow could be seen at the

cathode end of the tube, creating a device known commonly as the Geissler tube.

Becquerel built on this discovery by experimenting with different coatings on the inside

of the tube. In 1901, the American, Peter Cooper Hewitt, patented the first mercury

vapor lamp. This is considered “the very first prototype of today’s modern fluorescent

lights” [11].

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A fluorescent lamp, commonly categorized as an arc or vapor lamp, operates in a

completely different way than does a standard incandescent lamp. In an incandescent

lamp, light is simply a byproduct of electricity running through a highly resistive

filament. As electricity flows in the circuit of an incandescent lamp, high temperatures in

the filament cause it to glow and emit light. In a fluorescent lamp, light is produced

when electricity is applied to different gas mixtures contained in a vacuum tube. So the

direct result of operating a fluorescent lamp is visible light, while an incandescent

dissipates 90% of the input electrical power as heat.

Fluorescent lamps are low pressure, gas-discharge devices that utilize electricity

to excite mercury vapor suspended in a gas (normally argon or xenon). An arc is created

when electricity runs through a cathode (coiled tungsten electrode typically coated with

barium, strontium and calcium oxides – electron-emitting substances) at each end of a

tubular lamp, sending current through mercury vapors in the tube. As electricity passes

through the lamp circuit, the cathode heats up and emits electrons that collide with

mercury atoms, displacing electrons in these atoms from their natural orbit and forcing

them into a higher, unstable energy state [12]. As the displaced mercury atom’s electron

returns to a stable energy level, it gives off some visible, but mostly invisible (ultraviolet)

radiation (generally along principle lines of 254, 313, 365, 405, 436, 546, and 578 nm).

This ultraviolet radiation is transformed into visible radiation by a special phosphor lining

on the inner side of the lamp tube which lengthens the “UV wavelengths to a visible

portion of the spectrum” [12]. In other words, ultraviolet photons are absorbed by

electrons in the atoms of the phosphor coating which causes a similar energy level jump,

and drop, emitting another photon of wavelength perceptible by the human eye. “The

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phosphors are generally selected and blended to respond most efficiently to 254 nm, the

primary wavelength generated in a mercury low-pressure discharge” [1]. Fig. 11

illustrates this phenomenon in fluorescent lamps [12].

Fig. 11. Illustration of light production in general fluorescent lamp [Taken from Ref. 12].

Fluorescent lamps are commonly designated by their shape and diameter which

follow a particular nomenclature. A letter designates the shape of the lamp while a

number (indicated in eights of an inch) designates the diameter. For instance, T-8 refers

to a tubular bulb 8/8 in. (1 in. in diameter). Lamps can either be tubular or U-shaped.

Most lamps seen in the industrial sector are tubular. Lamps vary in diameter from 2 mm.

(0.25 in. T-2) to 54 mm. (2.125 in. T-17). Their lengths vary from 100 to 2440 mm. (4 to

96 in.) [1].

Similar to HID lamps, fluorescent lamps use two electrodes which are

hermetically sealed inside the tube, one located at each end. These cathodes are designed

for either cold or hot operation, but because hot operation (arc mode operation) is

inherently more efficient, most fluorescent lamps are designed in this way. In arc mode

operation, the hot cathode is typically constructed from either a single strand of tungsten

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wire or a coiled piece of tungsten wire around which another finer piece of wire is

uniformly wrapped. Thus, the electrode is called either a coiled-coil electrode or a triple-

coil electrode, respectively. Both electrode types are coated with an electron emission-

enhancing substance, which is commonly a mixture of alkaline earth oxides. As current

passes through the tungsten coil, temperatures of 1100 °C (2012 °F) are reached, causing

the coating to emit a large quantity of electrons [1].

The lamp tube is commonly filled with mercury vapor, typically maintained at

1.07 Pa (the vapor pressure of liquid mercury at 40 °C – the optimum bulb wall

temperature of operation for which most lamps are designed), and a rare gas or

combination of gases at low pressure to facilitate ignition of the discharge [1]. Common

rare gases used in lamps include: argon, krypton, neon, and xenon. An integral part of

operation is the ability of the lamp to develop and maintain a discharge between the two

electrodes. Thus, the attainment of optimum temperatures and pressures inside the tube

is critical for the ionization of mercury gas, which ultimately determines the fate of a

consistent discharge.

The phosphors which coat the walls of each fluorescent tube will establish the

color of light produced by each lamp. Lamps with markedly different spectral power

distributions are available for purchase, and thus, it is often a chore selecting a lamp with

the most appropriate color characteristics. “Popular fluorescent lamps use three highly

efficient narrow-band, rare-earth activated phosphors with emission peaks in the short-,

middle-, and long-wavelength regions of the visible spectrum. These triphosphor lamps

can be obtained with high color rendering, improved lumen maintenance, and good

efficacy with correlated color temperatures between 2500 and 6000 K relative to

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halophosphate lamps” [1]. However, rare earth phosphors are rather expensive and thus

longer lamps (T-5 – T-12) typically employ a two-coat system. The less expensive

halophosphate is located on the inside, while the more expensive rare earth blend resides

on the outside, closest to the mercury discharge. A lamp utilizing this configuration of

phosphors will typically have a spectral power distribution with a closer resemblance to

that of the rare earth phosphors. Fig. 12 was taken from the Illuminating Engineering

Society of North America [1]. The three distinct illustrations within the figure elucidate

some key areas of function in a fluorescent lamp.

3.2 Linear Fluorescent Lamps Types

The following discussion highlights some aspects of linear fluorescent lamps in

the most common available sizes. Descriptions are pithy and not meant to provide a

comprehensive review of each lamp type.

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Fig. 12. Cutaway view of some common fluorescent lamps: (a) typical rapid start fluorescent lamp and the production of light (b) lamp electrode construction (c) detail of the electrode [Taken from Ref. 1].

3.2.1 T-12 Lamps

Despite the influx of newer, more efficient fluorescent lamps and the passing of

the National Energy Policy Act of 1992 (EPACT) which banned their production after

1995, T-12 fluorescent lamps are still the most commonly used source of fluorescent

light. T-12 lamps, possessing a tube diameter of 1.5 in., are commonly seen in lengths of

4-ft. and 8-ft [1]. More specifically, the 40-W, 4-ft, rapid-start T-12 lamp had

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considerable control of the market for fluorescent lighting until more efficient and

efficacious lamps exposed its inefficiencies. Today many of the nation’s industries still

use the inefficient T-12 lamp, mainly in a reduced 34-W configuration, but most are

making the switch to more efficient T-8 models when replacements are needed. Despite

a growing awareness of more viable replacements to the T-12 lamp, many facilities are

hesitant to invest in expensive capital projects to replace these lights. T-12 lamps have

clearly seen their days of dominance, however; and today, T-8 and T-5 lamps are slowly

uprooting the industrial sector’s workhouse due to numerous energy cost saving benefits.

3.2.2 T-8 Lamps

T-8 lamps represent a viable, energy-efficient replacement to the obsolescent T-

12 lamp. They are a family of 1 in. diameter straight tube fluorescent lamps which are

manufactured in many of the same lengths as T-12 lamps. The 4-ft version is the most

common, consuming approximately 32 W. Other common lengths are 2-,3-,5-, and 8-ft.

Though T-8 lamps are interchangeable with T-12 fixtures of similar length, a different

ballast must be used in replacement. Most T-8 lamps utilize higher efficiency electronic

ballasts which facilitate even better performance. Additionally, these thinner lamps

“enable better photo-optic control of the light produced by the fixture, increasing

efficiency and providing uniform distribution of its light output” [5]. The smaller

diameter also allows for a more efficient use of the expensive rare earth phosphors. T-8

lamps are also offered in popular energy savings wattages of 25 W, 28 W, and 30 W

where a combination of ballasts with varying ballast factors can be employed to achieve a

desired quality and quantity of light for numerous applications [1].

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T-8 lamps installed in multi-lamp fixtures have recently gained momentum in the

market for fluorescent high-bay fixtures because of their proven ability to provide good

optical control and steady, uniform light. For high fixture mounting heights (those

typically seen in high-bay applications), high-lumen, 32-W T-8 (Super T-8) lamps are

often specified. A drawback of using T-8 lamps at this height is that more lamps may be

required to produce the same wattage as a 400-W metal halide in a retrofit. Currently

multi-lamp fixtures of both T-5 and T-8 lamps are being employed for both high and low

bay applications (although T-5 fixtures are considered a better option at heights above

20ft.). Common high-bay applications utilize 6- high-lumen, T-8 lamps (typically 3,100

initial lumens per lamp) with high ballast factor ballasts (1.14-1.20) and very efficient

reflectors.

3.2.3 T-5 Lamps

T-5 lamps also represent a suitable, energy-efficient replacement to the T-12

lamp. These lamps pose an even greater threat because they are smaller in diameter than

the T-8, offering the same benefits but on a different level. According to the National

Electrical Manufacturers Association (NEMA), T-5 and T-5HO lamps comprise 2% of

the fluorescent lamp market. This should, however, come as no surprise considering it

has taken almost a decade for T-8 lamps to gain their 33% share of the market from the

entrenched T-12 lamp.

The T-5 lamps compose a family of 5/8 in. diameter straight tube lamps, 40%

smaller than T-12 lamps, that utilize the appealing triphosphor technology. They are

designed to operate solely on electronic ballasts, and for most multi-lamp systems the

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newly refined programmed start ballast is considered optimal. This fact, in conjunction

with the fact that they are only available in metric lengths and bipin bases, renders them a

more difficult replacement for the T-12 lamp. Rather than just replacing the ballast for a

T-12 to T-8 change, the entire fixture must be replaced to change from either of these

lamps to a T-5 lamp. Despite making a retrofit rather difficult, these features are

generally beneficial to the T-5 lamp. Mainly, they allow for it to provide a higher source

of brightness and better optical control. Additionally, because they are so much smaller,

they are designed to provide optimum light output at 35 °C (95 °F) rather than the

common 25 °C (77 °F) [1]. For this reason it has been stated that T-5 lamps are better

than T-8 lamps for high-bay applications where greater ambient temperatures are more

common. Also, this higher optimum operating temperature allows for the design of more

compact luminaires, an extremely attractive feature responsible for the rise of T-5 high-

bay fixtures. Another important advantage of T-5 lamps is its use of barrier coating

technology. The smaller diameter lamp makes it more economical to use expensive

coatings that reduce the absorption of mercury by the tube’s glass interior and phosphor

coating. This barrier coating has dramatically reduced the amount of mercury needed to

operate the lamp (from 15mg to 3mg), and consequently, by reducing mercury absorption

which causes lamp light depreciation, increased maintenance of initial lumen output

values.

Typically fluorescents were not considered a viable option for high-bay

applications because they could not provide the source brightness that HID lamps could

at heights above approximately 20 feet. But the emergence of higher-output fluorescent

lamps with excellent performance qualities, and cooler-operating, multi-lamp (4 to 6

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lamps) fixtures has allowed T-5 (and in most cases T-8) luminairies to compete at these

heights.

Table 3. Comparison of Nominal Four-Foot Fluorescent Lamp Types

Comparison of 4-foot

Fluorescent Lamps T5HO T8

CRI 82 85

Color Temperature 3,000/3,500/4,100/5,000/

6,000K

3,000/3,500/4,100/5,000/

6,000K

Initial Rated Light Output 5,000 lumens @ 35°C

ambient

3,000 lumens @ 25°C

ambient

Nominal Lamp Wattage 54W 32W

Initial Lamp Efficacy 92.6 lm/W @ 35°C

ambient

93.8 lm/W @ 25°C

ambient

Lumen Maintenance 95% @ 8,000 hours 95% @ 8,000 hours

Maintained System

Efficacy

86.1 lm/W @ 8,000

hours and 35°C ambient

89.1 lm/W @ 8,000

hours and 25°C ambient

Rated Life (3hrs/start) 20,000 24,000

Source: Taken from Ref. 2. 3.3 Fluorescent Ballasts

The interaction between lamps and ballasts is one of the most significant factors

governing overall system performance. Various starting and operating methods for lamps

are provided by a multitude of different ballasts and it is of utmost importance to ensure

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that the ballast is chosen to match a particular application. These ballasts will often

provide a balance of certain characteristics like lamp life, energy efficiency, and

maintenance costs. Most fluorescent lamps used today operate on electronic ballasts

because of their inherent superiority over magnetic ballasts. They are significantly

cheaper for fluorescents than they are for HID lamps due to many decades of proven

performance and field acceptance. As previously noted, electronic ballasts will provide

energy savings over magnetic ballasts, but there are numerous reasons that their influence

on the fluorescent ballast market has been substantial. Among other advantages, they are

smaller, quieter, and lighter than their magnetic counterparts [25]. They operate at cooler

temperatures, are more efficient (better efficacy – high lumen per watt), provide longer

lamp life, and reduce the flicker and soft hum common in magnetic ballasts (because of

higher frequency operation) [25]. Three main types of fluorescent ballasts, categorized

by their lamp starting and operating methods, are seen consistently in application, but one

particular type, the programmed-start ballast, has garnered considerable acclaim for its

ability to operate with multiple controlling techniques in coveted high-bay applications,

and will thus be the focus of discussion.

3.3.1 Rapid Start Ballasts

A rapid start ballast applies continuous heat to the cathodes during the course of

operation of a fluorescent lamp. The heat and starting voltage are applied

simultaneously. This continuous heating of the cathodes reduces the necessary starting

voltage and allows the cathodes to reach a sufficient operating temperature. High starting

voltages are often the cause of tungsten sputtering and eventual lamp blackening; so a

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reduction in starting voltage likely increases the life of the lamp. The only drawback is

that additional power will be needed to provide continuous cathode heating.

Additionally, because the cathode heating and starting voltage are applied

simultaneously, a delicate balance must be reached for the optimal performance. The

cathodes need to be heated to the appropriate temperature before the arc is established.

But there is no guarantee that proper cathode temperatures will be reached prior to lamp

ignition. If the cathode temperature is below optimum and the voltage across the lamp

gets high enough to ignite the lamp, sputtering of the emissive material may ensue.

However, as will be discussed later, programmed start ballasts rectify this design

shortcoming (see section on programmed start ballast). Rapid start ballasts are very good

for lamps connected to occupancy sensors, photocells, or any other lighting control

devices where they might be switched on and off frequently. Note that additional

circuitry needed for cathode heating warrants a higher ballast cost [25].

3.3.2 Instant Start Ballasts

An instant start ballast will provide a high starting voltage to a fluorescent lamp

without prior cathode heating. Providing more of a “jump start” to the lamp, instant start

ballasts put undeniably more stress on the electrodes. An obvious reduction in energy

consumption will exist as extra power to provide heating is unneeded, but a shorter lamp

life because of repeated electrode material expulsion may outweigh the benefits of energy

efficiency if the lamp is employed for frequent switching applications [25].

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3.3.3 Programmed Start Ballasts

Programmed start ballasts are a variation or improvement to rapid start ballasts.

Their unique starting process markedly improves lamp life (50 percent in frequent

switching applications) and reduces the pitfalls associated with rapid start ballasts to

approach the energy saving potential of instant start ballasts. Programmed start ballasts

utilize this precise starting sequence, which is broken into well-established steps that

eliminate the deficiencies in other starting methods [26].

The ballast begins with the application of heat to the cathodes during a starting or

preheat interval, and voltage across the lamp is maintained at a low level. The duration

of this first step is preprogrammed in a ballast and is an integral part of successful

operation. The ballast provides heat (voltage) to the cathode until it reaches an optimum

temperature (at least 700°C) [26]. Voltage across the lamp remains at a low level until

this optimum cathode temperature is reached, preventing the lamp from igniting and

creating an unwanted glow current (lamp current that flows during the preheat interval –

causing lamp blackening and degradation) [25].

In the second step of operation, the ballast applies a voltage high enough to begin

ignition of the arc, but low enough to preserve emissive material on the cathodes. Both

step operating times and applied voltages are programmed into the ballast for better

performance, hence the name “programmed start.” Often, cathode heating is reduced

after lamp starting to provide additional energy savings with decreased power

consumption. Ultimately, programmed start ballasts are a better alternative for

applications that utilize lighting control devices as they are purported to provide 50,000

switching cycles (15 min. on/ 5 min. off) and a lamp life improvement of 10,000 hours in

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the these conditions [25]. They are simply gentler on the cathodes than either of the other

ballast types because they employ such a well-defined starting process. These ballasts

are currently being paired with multi-lamp T5HO fixtures for excellent optical control

and light quality when operated with a variety of light sensors and control devices.