Objectives Describe the lighting parameters Learn about lamps Define project 2

Objectives

• Describe the lighting parameters

• Learn about lamps

• Define project 2

Photometrics

• Luminous intensity [candela, cd] • Define the ability of light source to generate light (illumination) in

given direction

• Power – luminous flux [lumen, lm] • Quantity of light

• Illuminance – light power density [foot-candela, fc] [lux, lx] SI units

• Density of light (illumination) incident on a surface

• Luminance - surface brightness [foot-lambert, lm/ft2] • directional emission of visible light

Illuminance (E) depends on angle

Example:• Spot light with luminous

intensity I= 5000cd is aimed at painting at the wall 5 ft from the light and the angle φ=45°.

• What is the illuminance level (E) at the center of the painting?

Solution• Distance:

• Illuminance orthogonal to the beam

E=I/L2=5000/

Ebeam= 100 fc

• Illuminance orthogonal to the painting

Epainting= Ebeam/

Epainting=71 fc

25' L

2' )25(

25' L

2

Color of light• Color temperature is used to express the color

of the light

Surface color rendering

Depending on the light type the surface colors can be different

Depends on spectral energy distribution

Color rendering

lamp source can cause a color shift

Color rendering index (CRI)

• Indicate if a lamp source will cause a color shift.

• Definition:

CRI =100 for incandescing lamp with color temperature 3000K

Luminous efficacy

• Define the light output per unit of electric power input

Efficacy = Lumens/Watt

Lifetime of lamps

• Rated life of lamp is time elapsed when 50% of group of lamp remain burning.

Lumen deprecation

Data for fluorescent lamps

Lumen output fall during the life time

Ref: Tao and Janis (2001)

Types:

• Incandescent

• Electric discharge • Fluorescent • HID High-intensity Discharge Lamp

Incandescent• Thomas Edison first incandescent lamp

• Efficacy of 1.4 lumens/watt

• Life – 750 to 1000 hours

• 10 – 20 % decay in output

Specialty Incandescent Lamps

• Halogen

• Low voltage

• Long-life

• Infrared

• Interference filters

Is Dimming Bad For Incandescent Lamps?

- 10% lower Voltage

- 25% lower light

- life of lam doubles

Fluorescent Lamps

• Electrodes arc through mercury vapor

• Phosphors fluoresce in visible range

• Efficacy of 60 to 100 lumens/watt (after burn-in)

Ref: Tao and Janis (2001)

• 20,000 hour life for tubes

• Output falls off significantly (lumen deprecation)• We define mean lumens at 40% expected life

• Environmental hazard because of mercury

• Significant improvement with lumen deprecation and life with new types of fluorescent lamps

• Start of the lamp vary with type of fluorescent lamp

Fluorescent Lamps

Ballasts

• Why do we need ballasts?• Transformer –higher voltage• Limit the maximum flow of current - choke

• Types:• Magnetic

• Noisier, cheaper, less efficient (more heat)

• Electronic• Quieter, better power factor, more expensive• Lower harmonic distortion• Higher frequency

Comparison

• Incandescent: 40 W × 8760 hr/year = 350 kWh• Demand charges, maintenance, additional cooling• Uneven illumination

• LED: 1 W × 8760 hr/year = 8.8 kWh• 1/40th of the energy charges, lower demand, less

maintenance, lower cooling bills• More even illumination

High Intensity Discharge (HID)

• Arc through conducting vapor

• High temperature and pressure• Ceramic or quartz tubes• Glass protective casing

• Also need ballast (electric discharge lamps)

Ref: Tao and Janis (2001)

Types of HID LightingType Color Temp.

(K)Efficacy

(lumens/W)CRI Lifetime

(1000 hours)

Mercury 5710 20-60 15-50 24

HPSHigh pressure

sodium

2100 140 22-70 16-40

LPSLow pressure

sodium

1740(yellow)

200 ~0 10-201

Metal Halide

3600 ~100 <70 10-20

1minimal decline in output with aging

Issues with HID lighting

• Long start-up ~ minutes• Arc needs to stabilize, heat vapor

• Even longer restart

• Up to 40,000 hour life time

What is next in lamp technology

• LEDs - light emitting diodes• Semiconductor technology• Exit signs

• Electrodeless Lamps• Induction lighting• Microwave lighting

• High efficiency• Possible interference with wireless networks

• Nuclear Light Source

Comparison

Type Power (W) Lifetime

Incandescent 40 2 – 8 months

Fluorescent 10 – 25 1 – 2 years

LEDlight emitting diodes

~1 10+ years

Tritiumnuclear

0 10 – 20 years

Lamps are not the only thing

• Fixtures (luminaire)

• Application requirements

• Mounting

• Distribution