Dimming - part 1 - introduction to dimming

COURSE : DIMMING CONTROL

PART 1: INTRODUCTION TO DIMMING

CONTENT: 33

INTRODUCTION

Welcome to the Dimming Control course and its first part, Introduction to Dimming.

Dimming is the adjustment of light output over a specified range, with an important additional effect being a reduction in power input.

Dimming may be implemented using manual or automatic controls. Manual dimming is driven by visual/aesthetic needs and is used to achieve a certain look, mood, or visual condition. Automatic dimming, used to realize a range of strategies, is driven by energy cost savings and enables automatic changes in light level without irritating occupants.

For a light source to be dimmed, it must be designed to be dimmable, and it must be compatible with the dimmer.

Introduction to Dimming describes popular dimming strategies and how different light sources behave when dimmed.

LEARNING OBJECTIVES

In this Module, you will learn about:

• The purpose of dimming • Stepped versus continuous dimming • Dimming strategies for visual needs and energy management • Dimming for popular lamp types

PURPOSE OF DIMMING

Dimming provides greater flexibility from the lighting system, enabling users to have more control over their lighting conditions to support visual needs, and enabling enactment of energy management strategies in both occupied and unoccupied spaces that can reduce energy costs.

LIGHT LEVEL AND PERCEPTION

As light sources are dimmed, light output decreases but the human eye may perceive a higher light output and light level than is present. This is because the human eye overcompensates for diminished light level by allowing more light to enter its pupil. For example, dimming to 25% appears to be about 50% of full light level.

The effect is predictable according to the square law, which defines the theoretical relationship between light level and perceived brightness:

Perceived Light (%) = 100 x square root (Measured Light (%)/100)

Image courtesy of Lutron Electronics


An important issue related to light level perception involves whether users detect automatic dimming for an energy management purpose unrelated to visual needs, and whether they accept it.

Various organizations have studied the threshold for when users are likely to notice the lights are being dimmed, and concluded that a 15-20% reduction in light level is undetectable by a majority of users (Kryszgzuk and Boyce, 2001 and 2002, Shikakura et al, 2001, and Akashi and Neches, 2004).

Image courtesy of Lighting Research Center


National Research Council Canada subsequently studied how far lighting could be dimmed before users 1) detected it and 2) considered it intrusive (Newsham, 2009). The researchers found that in areas with above-average levels of daylight (HD), users were less likely to notice and were more likely to accept deep light level reductions compared to spaces with lower-than-average daylight levels (LD) or no daylight at all (ND).

This confirms that daylight-based dimming is likely to be non-intrusive, while suggesting applications for demand response.

Image courtesy of National Research Council Canada

STEP DIMMING

Dimming may be implemented in steps or across a continuous range.

Step dimming provides a limited choice of light levels, with two or more preset increments between OFF and full output. Typically, there is no fade between lighting states, so while technically the approach is dimming, the visual effect is the lights are abruptly switched to a lower state.

This approach is suitable for unoccupied spaces where lighting must be reduced but remain ON and occupied spaces where the instantaneous change in light level is acceptable.

Image courtesy of Universal Lighting Technologies

CONTINUOUS DIMMING

Continuous dimming enables light levels to be lowered or raised over a specified range, with smooth transitions between levels.

This provides a higher degree of flexibility for manual dimming control driven by application needs such as A/V presentation, mood setting, and so on. It also enables light output to be automatically reduced to save energy with a lower potential for irritating occupants, and is therefore the control method of choice for automatic control strategies in spaces occupied by people performing stationary tasks.


MANUAL DIMMING

Dimming strategies include manual/personal, driven by visual needs, and a variety of automatic strategies used for energy management.

Manual dimming provides flexibility to select light levels required for different uses of the space, such as mood setting in restaurants and optical viewing conditions for multimedia presentations and other uses in meeting rooms and classrooms.

TASK TUNING

Occupants in private and open offices can be given the ability to select light levels based on need or preference. In an open office, this would entail giving users control of the downlight component of dedicated overhead luminaires using a handheld remote or slider icon on their PC, as shown in this layout. (The uplight component might be controlled in unison based on schedule, demand response or daylight harvesting.)

Research studies indicate that giving users the ability to select light levels results in greater job and environmental satisfaction. One office lighting field study, conducted by the Canadian National Research Council, assessed average energy savings of 11% as an additional benefit.

Image courtesy of Ledalite Architectural Products

DAYLIGHT RESPONSE

Required by a majority of commercial building energy codes, daylight response or harvesting entails using a light sensor to monitor light levels and adjust electric light output to maintain a target light level, saving energy. Dimming is better suited for spaces where occupants work stationary tasks, luminaires are installed in the field of view, and/or where daylight availability fluctuates frequently throughout the day.

OCCUPANCY RESPONSE

In certain applications offering retrofit opportunity or where required by energy code, lighting may be reduced to save energy based on occupancy in:

• spaces that are partially occupied and where turning OFF zoned lights would be disruptive to users still in the space; and

• spaces that are unoccupied but where the lights must remain ON for safety and security, such as corridors and stairwells.

For example, in an open office, luminaires could be connected into zones that dim to OFF when all occupants in the zone exit the space. Similarly, luminaire-level occupancy sensors could accomplish this with dimming of individual luminaires mounted directly over workstations.

As another example, the output of luminaires in a stairwell could be stepped down when no occupants are present.

INSTITUTIONAL TUNING

Also called “high-end trim,” task tuning involves reducing lighting in a space based on IES-recommended maintained task light level requirements or user preference for individual spaces rather than the originally designed maintained light levels, which may be higher than needed.

Dimmable lighting can still be controlled as usual to implement other strategies such as manual control and daylight response. However, with task tuning, the high-end level is capped, resulting in permanent and potentially significant savings through dimming.

As lower light levels are the tradeoff of energy savings with task tuning, it is ideally suited to overlighted spaces, and works best for occupied spaces when tuning is adjusted based on occupant feedback.

ADAPTIVE COMPENSATION

This energy management strategy involves reducing light levels at night in spaces with non-critical tasks based on research that people prefer and need less light at night than during daytime. This type of strategy would typically be implemented based on a schedule.

DEMAND RESPONSE

In this energy management strategy, the control system responds to a signal from the local utility to reduce electric load during a grid emergency. Dimming is ideally suited to demand response, as it enables lighting load reduction without turning the lights OFF. The owner receives financial incentives such as special rates in return.

LUMEN MAINTENANCE DIMMING

This energy management strategy involves using a light sensor to monitor light level and automatically compensate for lamp lumen depreciation. (When closed-loop daylight dimming is implemented, this strategy automatically occurs.) As lighting systems are typically overdesigned to compensate for lamp lumen depreciation, energy savings are realized.

In the case of LED lighting, the controller can be programmed or assigned a sensor to underdrive the luminaire to deliver actual or projected constant light output over its life to maximize energy savings.

Image courtesy of Kevin Willmorth, LumenPriority.org

DIMMING RANGE

When designing for dimming, an important concept is the dimming range.

The dimming range expresses how low the driver or ballast can dim the connected light source. A light source with a dimming range of 100% to 5%, for example, can nominally dim from full light output to 5% of full output.

While this percentage may be the fraction of rated power, usually it is an expression of relative light output. For example, a lighting system at 25% dimming range produces 25% of its full light output, as shown with the below fluorescent lamp operated on a dimmable ballast.

Dimming range is a factor in whether the application is categorized as architectural dimming, which typically dims down to <1% and is driven by visual needs, or energy management dimming, which typically dims down to around 5-20% and is driven by energy savings. An application that intersects these categories is giving office users the ability to dim their overhead lighting over a desirable range.

LED DIMMING

LED dimming is used for visual needs and energy management and can also be used to separately dim colored or different-color-temperature white LEDs to tune color output. As with other lighting system types, successful dimming requires a dimmable power controller (in this case a driver) and that the dimmer and driver are compatible in dimming method.

The driver dims the LEDs using either pulse-width modulation (PWM) or pulse-amplitude modulation (PAM) methods. With both methods, light output can be dimmed precisely, predictably, and without visible flicker, depending on the quality of the product. The driver may be integrated with the power supply or remotely mounted.


LED DIMMING

LED lamps and luminaires may be dimmed using line- or low-voltage (0-10V, DALI, or DMX) methods. Dimming ranges of 100-20% and 100-1% are available, depending on desired capabilities and cost. The highest-performing products dim smoothly from 100-1%, while the lowest dim from 100-20% while exhibiting an inconsistent step-dimming effect.

Image courtesy of Lumenique, LLC

LED DIMMING

Dimming results in light output that is proportional to electrical input; an LED operating at 50% of its rated power will produce roughly 50% of its initial rated light output. As a result, light source efficacy (lumens/W) is stable across the dimming range until the low end, when efficacy may increase due to dimming reducing internal temperatures and producing higher light output.

While this is obviously positive in terms of efficiency, it also means that for manual dimming, light output and dimmer setting may drift out of proportion at the dimming range’s low end. Some higher-end products compensate for this effect.

Image courtesy of Lumenique, LLC

LED DIMMING

Because dimming reduces internal temperatures, it can extend LED light source life while also delaying color shift (towards blue) that occurs over time with phosphor-coated LEDs.

Image courtesy of Cree, Inc.

INCANDESCENT/HALOGEN LAMP DIMMING (LINE VOLTAGE)

Dimming of tungsten-filament incandescent lamps, including 120V halogen lamps, occurs when the lamp is operated at a voltage lower than its rating, producing smooth, continuous dimming from 100% to 0.1%.

Most dimmers use the phase control method, turning the lamps ON and OFF 120 times per second; dimming occurs by delaying the first half of the cycle, creating a proportion of ON/OFF time that relates to a distinct dimming level.

Dimming makes incandescent lamps appear visually warmer (amber/orange), lose efficacy as the filament loses heat, and potentially gain in lamp life as the filament experiences less wear and tear.

HALOGEN LAMP DIMMING (LOW VOLTAGE)

Low-voltage lighting can produce brilliant white illumination from a very compact source that installs with a higher degree of safety.

Line- and low-voltage lamps may be mixed on the same dimming circuit, but only if using a low-voltage dimmer compatible with the low-voltage load (do not use standard line-voltage dimmers with low-voltage lamps).

Dimming extends lamp life but may result in lamp blackening caused by tungsten evaporation; if this occurs, it is recommended to operate the lamp at full light output for 10 minutes to eliminate most of the blackening.

Image courtesy of Juno Lighting

HALOGEN LAMP DIMMING (LOW VOLTAGE)

The halogen lamp transformer may be magnetic or electronic; do not mix magnetic and electronic transformers on the same circuit and ensure that the transformer is rated as compatible with the selected dimmer.

Magnetic transformers use symmetric phase control, which results in a smooth OFF; dedicated dimmers for these transformers may have capacity rated in VA.

Electronic transformers use reverse phase control, which results in very smooth turn-ON; dimmers for these transformers are typically rated in W. Electronic transformer/dimmer combinations generally provide superior performance, eliminating dimmer and luminaire buzz, lamp flickering and other problems that can occur with dimming magnetic transformers.

Images courtesy of Lutron Electronics

COMPACT FLUORESCENT LAMP DIMMING

Compact fluorescent lamps, or CFLs, are available with dimmable ballasts. While pin-based lamp-ballast systems offer reliable dimming using low-voltage controls, matching self-ballasted CFL products with standard line-voltage incandescent dimmers can be problematic, resulting in the development of universal dimmers able to dim incandescent/halogen, dimmable CFL, and dimmable LED lamps.

The majority of dimmable CFLs are limited in dimming range to 10-30% of full output. Various lamps may exhibit issues such as “drop out” or shutoff before the slider reaches the bottom, lamps failing to turn ON at the low end of the dimming range (requiring the slider to be raised, resulting in “pop ON”), and lights turning OFF unexpectedly or flickering due to line-voltage fluctuations. They can also become cooler in color appearance as they dim, the opposite of incandescent lamps, which become warmer.

LINEAR FLUORESCENT LAMP DIMMING

Fluorescent lamps are dimmable using dimmable ballasts, which are designed to respond to control signals by changing the current flowing through the lamp, which reduces both lamp output and power.

Most dimming ballasts are programmed-start ballasts, which operate at a loss in efficacy of nearly 10% compared to fixed-output instant-start ballasts, though some boast an efficacy as high as standard instant-start ballasts. For the most efficient 4-ft. T8 ballasts, look for the NEMA Premium mark on the label.

Linear fluorescent lamps should be “seasoned” prior to dimming for 12 hours at 100% output per NEMA guidelines, or per manufacturer instructions.

Image courtesy of Philips Lighting Electronics


Most dimmable electronic ballasts operate with a linear relationship between dimming level and light output, but not dimming level and input watts. A 20% dim level, for example, will result in 20% of full light output but not 20% of full wattage. Efficacy generally decreases as lamps are dimmed. Below around 20%, no significant energy savings are achieved.

Image courtesy of the Lighting Research Center


Dimmable ballasts operate according to a dimming method, which may be analog (“step dimming,” 0-10VDC, phase control and wireless infrared) or digital (DALI, proprietary). Digital and 0-10VDC are four-wire low-voltage methods, two-wire phase control is a line-voltage method utilizing the line for both power and communication, and wireless infrared is a short-range wireless method. Selection of dimming method is typically based on the use of the space, desired range of dimming, wiring, lamp type, physical size and/or budget.

0-10VDC Two-wire phase-control Three-wire phase-control

Images courtesy of Lutron Electronics


Be sure to specify ballasts that are dimmable, lamps and ballasts that are compatible, and ballasts and controls that are compatible. Because analog ballast performance may vary across products, avoid mixing ballast types from different manufacturers in the same system. Also avoid mixing dimmable and non-dimmable loads on a dimmer circuit, linear lamps and CFLs in the same control zone, and different lamp types (e.g., incandescent and fluorescent) on the same dimming control. It is sometimes advisable to avoid mixing lamp wattages in the same dimming zone as well.

Image courtesy of Philips Lighting Electronics

HID LAMP DIMMING

HID lamps are capable of stepped and continuous dimming. Stepped dimming may be achieved using constant-wattage autotransformer. Shown here is a 350W pulse-start metal halide system with all luminaires turned OFF on a schedule using a control panel/timeclock, while four are separately circuited and controlled with stepped dimming ballasts for 50% reduction for night and emergency lighting.

Image courtesy of WattStopper

HID LAMP DIMMING

Continuous dimming is available with high-performing electronic HID ballasts. These ballasts provide superior performance while typically dimming from 100% to 50% of lamp power.

Images courtesy of OSRAM SYLVANIA and Philips Lighting Electronics

HID LAMP DIMMING

As with fluorescent dimming, efficacy declines over the dimming range for HID stepped and continuous dimming ballasts; shown here is a 400W coated metal halide lamp tested by the Lighting Research Center from 100% to 50% of lamp power.

NEMA recommends avoiding dimming of HID lamps below 50%, as this can degrade lamp life by up to 90%—voiding lamp warranties—while also affecting efficacy, color and lumen maintenance. NEMA further recommends that the lamps be operated for at least 15 minutes before dimming (or 30 minutes if the lamp is extinguished due to a voltage interruption).

Note that HID lamps may experience color shift and lower CRI during dimming, particularly clear lamps. Clear metal halide lamps, for example, will shift up to 1500K, according to the Lighting Research Center—from white to blue-green.

Image courtesy of Lighting Research Center

NEON/COLD CATHODE DIMMING

Neon and cold cathode lamps operate similarly to fluorescent lamps but use a solid metal electrode operating at a low temperature. The lamp can be dimmed without impacting service life using a dimmable ballast (electronic ballast recommended). These ballasts can dim from 100-1% and start instantly at the lowest dim level.

Image courtesy Cathode Lighting Systems

YOU’RE FINISHED

Well done! You have completed Introduction to Dimming and are now ready to proceed to Dimming Controls. You are also now eligible to take this Learning Module’s comprehension test for credit towards your education goals.

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Dimming - part 1 - introduction to dimming