testing led lighting fixtures and comparing them to ... · testing led lighting fixtures and...

11© 2008 Rensselaer Polytechnic Institute. All rights reserved.

Testing LED Lighting Fixtures and Comparing Them to Traditional

Lighting Fixtures

N. Narendran, Ph.D.Lighting Research Center

Rensselaer Polytechnic Institute

Troy, NY 12180, USA

euroLED 2008 WorkshopJune 5, 2008


AcknowledgmentsAcknowledgments

euroLED 2008 organizers

ASSISTASSIST Program sponsors

LRC staff and students› Andrew Bierman, John Bullough, Mariana Figueiro, Jean Paul

Freyssinier, Chris Gribbin, Yimin Gu, Lalith Jayasinghe, Russ Leslie, Howard Ohlhous, Conan O’Rourke, Martin Overington, Mark Rea,Patricia Rizzo, Jennifer Taylor, Yutao Zhou, Keng Chen, Tianming Dong, Han Lei, Yi-Wei Liu, and Yiting Zhu.


LEDLEDLEDs – Will soon be one of the light source choices for illumination applications.

The potential for reduced energy use and lower maintenance costs are two key attributes of this rapidly evolving technology that have generated so much interest for its use.

PhilipsPhilips – CK


Need for metricsNeed for metrics

Applications community interested in using LEDs

Rapid development of LED technology

Many commercial products for general illumination› Some products have exaggerated claims

› Insufficient performance data available

Failed applications can hurt the entire industry

Many agencies are actively working on standards› Insufficient understanding of technology can lead to bad

standards


Presently, there are many light sources available to cater to lighting needs

• Incandescent• Fluorescent• HID• LED

What do end-users care about?• Good quality lighting• Reliable technology• Cost effective (low energy and maintenance cost)• Easy to buy and replace if needed

Metrics have to be technology neutral

LightingLighting

IncandescentHalogen

CFL HID LED

LSGOSI Philips GE


ASSISTASSIST recommendsrecommends

Application guides› Recommendations for using LED light

fixtures in applications• General guide to applications• Guide to selecting LED luminaires

Recommendations for testing and evaluating LED luminaires› Proposed test methods

• Are technology-independent• Consider application environment

Objective: To develop a series of publications that provides useful information to end users



Recommendations for testing and evaluating› LED life for general illumination applications› Directional lighting luminaires› LED light engines › Under-cabinet lighting luminaires› Freezer case lighting luminaires (in preparation)› Outdoor lighting luminaires (in preparation)

http://www.lrc.rpi.edu/programs/solidstate/assist/index.asp


ASSISTASSIST recommendsrecommendsRecommendations for Testing and Evaluating

Luminaires Used in Directional Lighting


Changing traditionsChanging traditions

Lighting specifiers use photometric data to select and use suitable luminaires› Traditionally, photometric testing is performed at an

ambient temperature of 25°C.› Selecting LED downlights for an application on the basis of

published photometric data could result in considerably lower light levels in the space than designed, leading to disappointment.

ASSISTASSIST is proposing the use of board temperature, instead of ambient temperature, and to measure luminaire performance in conditions similar to the application environment.


Directional lighting test methodDirectional lighting test method

ASSISTASSIST recommendsrecommends proposed three environmental conditions to test fixtures: › Open air: Here the light source and the

driver have plenty of ventilation around them.

› Semi-ventilated: Here the light source and the driver have limited ventilation around them (similar to Non-IC).

› Enclosed: Here the light source and the driver have almost no ventilation around them (similar to IC).


Sphere photometrySphere photometryTemperature, Ts, is measured while operating the fixture in the three environments.

Fixture is placed inside a heated enclosure, which is placed inside the integrating sphere.

Data gathered once the temperature, Ts, reaches application temperature.

Heater

Lamp

Driver

Heated enclosure

Feedbackcontrol

Ts


Luminaire testing Luminaire testing

Several commercial LED fixtures are being tested in the three environments (per ASSISTASSIST recommendsrecommends)› Open air› Semi-ventilated› Enclosed

Short-term testing› Flux and color

Long-term testing› Lumen depreciation and life (L70)› Color shift


Flux (lumens) & Efficacy (lm/W)Flux (lumens) & Efficacy (lm/W)Well-designed luminaires maintain light output, even in hotter environments. However, poorly designed luminaires have significantly lower light output (more than 30%) in IC-condition.Traditional test methods would not have provided this information.

236

649583

263212

678

446

223

643

396

183

0100200300400500600700800

Fixture A26W

Fixture B26W

Fixture C12W

Fixture D30W

Flux

(lum

ens)

Open air Non-IC IC

10

22

54

8917

7715

5457

0

10

20

30

40

50

60

70

Fixture A26W

Fixture B26W

Fixture C12W

Fixture D30W

Effic

acy

(lm/W

)

Open air Non-IC IC


Board temperature (Board temperature (°°C)C)

With increasing Tj the life shortens › Generally half the life for every 10°C increase

83 °C 87 °C

42 °C

80 °C95 °C

107 °C

50 °C

90 °C

115 °C 119 °C

60 °C

-0

20

40

60

80

100

120

140

Fixture A26W

Fixture B26W

Fixture C12W

Fixture D30W

Boa

rd T

empe

ratu

re (d

eg C

)

Open air Non-IC IC


Lumen depreciation & color shiftLumen depreciation & color shift

In the IC condition:Life (L70) is less than 3000 hrsThe color shift is greater than a 36-step MacAdam ellipse (reached within 3000 hrs)

Fixture A - 26W LED Downlight

50%

60%

70%

80%

90%

100%

110%

100 1,000 10,000Time (hours)

Rel

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Enclosed Semi-ventilated Open air

83 °C95 °C115 °C

Open airNon-ICIC

Fixture A - 26W LED Downlight

0

10

20

30

40

50

100 1,000 10,000Time (hours)

Mac

Ada

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llips

es



Fixture B - 26W LED Downlight

50%

60%

70%

80%

90%

100%

110%

100 1,000 10,000Time (hours)

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In the IC condition:Life (L70) is less than 3000 hrsThe color shift is greater than a 19-step MacAdam ellipse (reached within 4000 hrs)

87 °C107 °C119 °COpen airNon-ICIC

Fixture B - 26W LED Downlight

0

10

20

30

40

50

100 1,000 10,000Time (hours)

Mac

Ada

m E

llips

es



Fixture C - 12W LED Downlight

50%

60%

70%

80%

90%

100%

110%

100 1,000 10,000Time (hours)

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Even in the IC condition:Life (L70) seems very longThe color shift is within a 4-step MacAdam ellipse (in the 3000 hrs)

42 °C50 °C60 °C

Open airNon-ICIC

Fixture C - 12W LED Downlight

0

2

4

6

8

10

100 1,000 10,000Time (hours)

Mac

Ada

m E

llips

es



Fixture D - 30W LED Downlight

50%

60%

70%

80%

90%

100%

110%

100 1,000 10,000Time (hours)

Rel

ativ

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ght O

utpu

t


80 °C90 °C

Open airNon-IC

Even in the IC condition:Life (L70) seems very longThe color shift is within a 3-step MacAdam ellipse (in the 3000 hours)


Fixture D - 30W LED Downlight

0

2

4

6

8

10

100 1,000 10,000Time (hours)

Mac

Ada

m E

llips

es

Semi-ventilated Open air


SummarySummaryOut of the 4 fixtures presented here, only one showed results acceptable for general lighting, considering:› Light output› Efficacy› Lumen depreciation› Color shift over time

“ASSIST recommends” test methods:› Provide more useful information for selecting LED

directional lighting luminaires› Help differentiate between good and poor performing

LED luminaires in terms of light output and life


ASSISTASSIST recommendsrecommendsRecommendations for Testing and Evaluating LED Light Engines Used in Lighting Luminaires


Why LED light engines?Why LED light engines?Manufacturers often design families of decorative luminaires. › Sconces, pendants, table and floor

lamps• These luminaires can provide a

coordinated look while serving different functions

A large number of decorative luminaires can use a common light source (LED light engine).Photometric testing is not a feasible concept for such luminaires.

Driver

LED/LED array

Heat Sink

LED Light Engine

Bruce Kaiser


LED light engine performanceLED light engine performance

LED performance is affected by the heat at the LED junction. › The thermal environment near the

LED is altered depending on how the luminaire components are built around the LED module.

LED light engine: LED, heat sink, and driver.

How can a decorative luminaire manufacturer evaluate the performance of an LED light

engine when used in a luminaire?


Proposed methodProposed method

1. Temperature sensors are attached to the LED and the driver at the manufacturer-specified locations.

2. The LED light engine is placed inside a thermal test chamber.

3. The heater is turned on until Ts reaches 40% (and 60% and 80%) of Tjmax (specified by the LED manufacturer)

4. Photometric and electric quantities are measured at these three temperature.

5. Life testing is conducted at these three temperatures as well.

Driver

LED/LED array

Heat Sink

Heater Insulation

Temperature sensor (Ts)

Temperature Sensor (Tc)

Integrating sphere

Heater

LED light engine

Driver

Heated chamber

Tc

Ts

Feedback control to heater

LED/LED array

Heat Sink

LED light engine performance is measured as a function of temperature


Proposed methodProposed methodEstimating LED light engine performance in a luminaire

› Temperatures Ts and Tc are measured while the light engine is operating in a luminaire in its operating environment.

› The performance parameter is estimated from the plots shown below.

Ts (°C)

Flux (lm)

Ts (°C)

Life(L70) (hrs)

Ts (°C)

CIE x,y


Test method validationTest method validation

LED light engine inside a heated enclosure.


Test Results Test Results –– A sample 9 LED light engineA sample 9 LED light engine

B

0.38

0.39

0.40

0.41

0.42

60 70 80 90Ts (deg C)

CIE

x,y

LED module CIE x LED module CIE yLED Fixture CIE x LED Fixture CIE y

B

0

100

200

300

400

500

600

60 70 80 90Ts (deg C)

Flux

(lum

ens)

LED module LED Fixture

Test results show good agreement between estimated and measured results (within 3%)› LED Fixture Ts = 77°C


SummarySummary

Photometric testing is not a feasible concept for decorative luminaires.

Developing a relationship between LED light engine performance parameters (flux, efficacy, CCT, CIE xy, and CRI) and the board temperature (Ts) is useful for estimating the performance of an LED light engine in any lighting fixture.



Under-cabinet Lighting Luminaires



Determine color› Use CCT, CRI, and CIE xy provided by light

source manufacturer

Measure fixture life› Follow life-testing guidelines from

ASSIST recommends: LED Life for General Lighting


Proposed test methodProposed test method

Light on the task area is what matters

Application efficacy = Total lumens on the taskTotal fixture power


Test data per Test data per ASSISTASSIST recommendsrecommends

05

10152025303540

Hal. T5 A T5 B T8 C T2 D LED A LED B LED C LED D LED E LED F

App

licat

ion

Effic

acy

(lm/W

)

Hal. T5 A T5 B T8 C T2 D LED A LED B LED C LED D LED E LED FFixture length (in) 12 12 12 20 18 24 24 12 12 21 12

Horizontal flux (lm) 53 91 72 180 199 95 77 87 111 172 173Horizontal average (lux) 96 163 129 277 307 128 104 155 199 252 311

Horizontal uniformity (max:average) 4:1 2:1 2:1 2:1 2:1 2:1 4:1 2:1 2:1 2:1 2:1Verticalflux (lm) 23 107 97 256 286 64 21 65 69 199 109

Vertical average (lux) 49 230 210 473 528 103 34 140 149 350 235Vertical uniformity (max:average) 4:1 3:1 4:1 4:1 3:1 3:1 3:1 4:1 2.5:1 2:1 3:1

(Fixture+Driver) Input power (W) 18.1 8.2 6.9 13.8 14.7 13.5 8.0 8.8 7.7 10.78 7.6(Fixture+Driver) Voltage (V) 119.0 119.5 119.0 118.8 119.2 118.3 118.9 24.0 119.8 119.8 120.0(Fixture+Driver) Current (A) 0.16 0.11 0.11 0.20 0.22 0.12 0.13 0.37 0.07 0.199 0.06

Ambient temperature (C) 23 23 22.9 23 23 23 23 23 23 24.6 23Fixture operating temperature (C) 38.2 33.6 40.1 44.8 41.9 37.7 28.2 41.4 30.6 35.2 35.5

Application flux (lm/ft) 76 198 169 262 324 80 49 152 180 212 283Application Efficacy (lm/W) 4 23 23 30 33 11 12 17 23 34 37

Fixture light output (lm) 88 281 420 623 616 194 151 222 417 420Fixture Efficacy (lm/W) 5 33 57 42 42 14 18 29 38 56

CCT 2591 3044 3965 2813 3223 2943 2868 5887 3500 7542CRI 100 87 86 82 78 73 65 76 73 71

Driver input power (W) 18.4 8.6 7.4 14.7 14.6 13.9 8.2 7.8 10.9 7.6

Grid measure

Sphere measure

ASSIST Reccomends MethodASSIST Recommends Method


Test dataTest data

0

10

20

30

40

50

60

Halogen F8T5 sample 1

F8T5 sample 3

LEDprototype 1

LEDprototype 2

Effic

acy

(lm/W

)

Application Efficacy (lm/W) (Fixture+Driver) Efficacy (lm/W)

0

10

20

30

40

50

60

Halogen F8T5 sample 1

F8T5 sample 3

LEDprototype 1

LEDprototype 2

Effic

acy

(lm/W

)

Application Efficacy (lm/W) (Fixture+Driver) Efficacy (lm/W)

-12%+32%


Sample reportSample reportGrid data allows for the evaluation of beam qualityTs measured in the application environment is a good predictor of life


SummarySummary

For under-cabinet fixtures› Application efficacy is a more meaningful metric

for system comparison• Light where you need it

Some manufacturers already provide illuminance data on the task



Freezer Case Lighting Luminaires

Fluorescent LED


Please notePlease note……

The information contained in this ASSISTASSIST recommends presentation is preliminary and still under investigation. This is for discussion purposes only. Please do not distribute or cite.

Once the ASSIST documents are finalized, we will place them on the LRC ASSISTASSIST Web site.


Light source performanceLight source performanceThe performance of LED and fluorescent lamps is affected by the operating temperature› Tj – LEDs › Cold spot – fluorescent lamps

Relative Light Output

0%

20%

40%

60%

80%

100%

120%

140%

0 °C 10 °C 20 °C 30 °C 40 °C 50 °C

LED Pin Temperature (°C)Ambient Temperature (°C)

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IESNA Handbook, 9th Edition



Total lumens on the task› Flux on the task area at application temperature

Total power› Fixture power + extra power used by the freezer at

application temperature

Application efficacy = Total lumens on the taskTotal power

Photometric performancePhotometric performance



Step 1: Task lumens measured at room temperature (25°C)› Measurement plane

• 5 ft by 5 ft

› Grid size• 6 in by 6 in

› Lamp-plane distance• 6 in

› Monitor lamp temperature • Ts for LEDs• Cold spot for fluorescent lamps

5 ft

5 ft6 in

6 in

ФФ = = ΣΣ EijEij ×× AA




Step 2: Light source performance is determined as a function of temperature

Ts (°C)

Flux (lm)

Ts (°C)

CIE x,y




Step 3: Total lumens at application temperature› Lamp temperature is measured at application condition› Lumens measured in Step 1 (at room temperature) is

adjust using the % light output measured in Step 2 (at the application temperature)

› Color values are measured at application temperature


Ts (°C)

Flux (lm)

Ts (°C)

CIE x,y


Proposed method Proposed method –– Total powerTotal power

Step 4: Total power measurement› The luminaire is placed in a test freezer.

› Input power per hour to the freezer is measured in two conditions after the temperature has stabilized:

• Fixture OFF (baseline)

• Fixture ON

› The extra power demanded by the freezer is calculated by subtracting the effective power with fixture OFF from ON.

Total power = Luminaire power while operating inside the freezer + Extra power demanded by the freezer

Energy performanceEnergy performance

Study setup


Task lumens (at room temperature) = 1720 lmTask lumens (at room temperature) = 1720 lm

1 3 5 7 9 11 13 15

S1

S3

S5

S7

S9

S11

S13

S15

1 3 5 7 9 11 13 15

S1

S3

S5

S7

S9

S11

S13

S15

1 3 5 7 9 11 13 15

S1

S3

S5

S7

S9

S11

S13

S15

Illuminance distribution

on test grid (scale in lx)

5 ft

5 ft 6”

Test method validationTest method validationLamp T8 Fluorescent Lamp

Position Center, Normal to PlaneDistance (in) 4

Task lumens at 25C (lm) 1720Task efficacy at 25C (lm/W) 56

Average illuminance (lux) 741Max illuminance (lux) 4670Min illuminance (lux) 37

Uniformity (Max:Average) 6.3Ballast input current (Arms) 0.258Ballast input voltage (Vrms) 119.7

Ballast input power (W) 30.5Fixture forward current (Arms) 0.177Fixture forward voltage (Vrms) 147

Fixture power (W) 25.3Lamp center temperature (C) 32.5

Lamp end temperature (C) 38.6Ballast temperature (C) 40

Ambient temperature (C) 24


Example: T8 fluorescent lampExample: T8 fluorescent lamp

Relative Light Output vs. Cold Spot Temperature

0%

20%

40%

60%

80%

100%

120%

-15 -10 -5 0 5 10 15 20 25 30 35 40

Lamp Cold Spot Temperature (C)

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Derating factor for a given application Tcold spot

Total lumens on the task at 8°C = 1720 x 0.32 = 550 lm


Total power & Application efficacyTotal power & Application efficacy

Luminaire power at freezer temp. = 28 W

The extra power demanded by the freezer = 18W

Total power = 46W

Application Efficacy = 550/46 (lm/W) = 12 lm/W


SummarySummary

Task lumens at application condition is estimated by characterizing the lighting luminaire performance as a function of temperature.

Total power at application condition is estimated by adding the extra power demanded by the freezer to dissipate lighting fixture heat to the fixture power at application temperature.

Application efficacy = Total lumens on the taskTotal power



Outdoor Lighting Luminaires


Please notePlease note……

Work in-progress….

The information contained in this ASSISTASSIST recommendsrecommends presentation is preliminaryand still under investigation. This is for discussion purposes only. Please do not distribute or cite.

Once the ASSIST documents are finalized, we will place them on the LRC ASSISTASSIST Web site.



ASSIST recommends…Outdoor Lighting› Test and evaluation method for luminaire› Initial scope: Parking lot lighting

ASSIST recommends…Visual Efficacy› Unified system of photometry to characterize

any light source at any light level

Energy efficiency in this application is achieved by:› directing the light to where it is needed› using a light spectrum that helps the visual performance



Amount of flux illuminating the task plane is the most useful, not all the flux that exits the luminaire.› Application efficacy is calculated using

illuminance measurements made on a grid or calculations using photometric data

Application efficacy = Total lumens on the taskTotal fixture power



Typical testing geometry (task area) for each type of light distribution (Types I to V) on the task plane

Luminaire Lateral Distribution TypesDiagram source: NLPIP Specifier Reports:

Parking Lot and Area Luminaires


Proposed method: ExampleProposed method: ExampleI. Calculating the application efficacy of 2 Type

III parking lot luminaires:

› 150W HPS – full cutoff› 208W LED

› 30’ ~ 9.1 m mounting height (MH)



Parking lot with contribution from 9 pole locationsParking lot with contribution from 9 pole locations•• Pole spacing and number of luminaires per pole Pole spacing and number of luminaires per pole depend on distribution type and mounting height (MH)depend on distribution type and mounting height (MH)

Vertical planes measure 6Vertical planes measure 6’’ x 6x 6’’(1.8 m x 1.8 m)(1.8 m x 1.8 m)


Proposed method: ExampleProposed method: Example

150'

120'

150‘ pole spacing

pole location – plan view

120‘ pole spacing

Calculation areawith

contribution from 9 poles

pole layout – perspective view

••The calculation plane is set up to calculate illuminance at the The calculation plane is set up to calculate illuminance at the center of 1center of 1’’x1x1’’ squares.squares.••Total luminous flux on the horizontal grid can be calculated by Total luminous flux on the horizontal grid can be calculated by multiplying the multiplying the illuminance value at each point by the area of each grid square.illuminance value at each point by the area of each grid square.


Example: ResultsExample: Results

EfficacyLight output

5.7 lx

3.2 lx12.7 lx

49.2 lm/W

68.6 lm/W106.7 lm/W

1.7:10.5 lx

20:10.3 fc

1.18 fc

9,306 lm

12,960 lm16,000 lm

* Contribution from 9 pole locations (18 luminaires total)

max:minminimum

Vertical illuminance*:max:minminimumaverage

Horizontal illuminance*:

On horizontal grid(one luminaire only)

LuminaireLamp

1.6:12.5 lx0.2 lx

16:13.2 lx0.3 fc

13.7 lx1.27 fc

49.1 lm/W10,206 lm

55.6 lm/W11,572 lm-NA

EfficacyLight output

Luminaire 1150 W HPS(189 W)

Luminaire 2160 1W LEDs(208 W)


ASSISTASSIST recommendsrecommendsOutdoor Lighting – Visual Efficacy


Light for the visual systemLight for the visual system

The unified system of photometry is a bridge from photopic to scotopic luminous efficiency functions through the mesopic region

StarlightStarlight MoonlightMoonlight Dim interiorsDim interiors Office lightingOffice lighting DaylightDaylight

ScotopicScotopic MesopicMesopic PhotopicPhotopic

Radiant EnergyRadiant Energy

0.00

0.25

0.50

0.75

1.00

400 500 600 700Wavelength (nm)

V(λ)V’(λ)Luminous efficiency

XX


Foveal + peripheral visionFoveal + peripheral visionThe relative proportion of photopic (V10λ) and scotopic (V’λ) luminous efficiency for peripheral vision at a given (mesopic) light level (He et al., 1997; 1998)

› At high light levels, x = 1› At very low levels, x = 0

Vmes = (x) V10λ + (1 – x) V’λ

0.00

0.25

0.50

0.75

1.00

400 500 600 700Wavelength (nm)

Luminous efficiency

In this example,

x = 0,40

L = 0,22 cd/m²

Vmes = (x) V10λ + (1-x) V’λ(mesopic = cones + rods)

VVmesmes = (x) V= (x) V1010λλ + (1+ (1--x) x) VV’’λλ(mesopic = cones + rods)(mesopic = cones + rods)


A practical systemA practical system

Rea et al. (2004)Rea et al. (2004)


Example: HPS vs. LEDExample: HPS vs. LED

Information needed:› Photopic light level (luminance, cd/m2)

› Scotopic-to-photopic (S/P) ratio of thelight sources• HPS: 0.62 to 0.66;

– example 0.65• LEDs: 1.68 to 2.31*

– example 2.15*Bin and manufacturer specific

Illuminance (E) = 12.7 lxLuminance (L) = E × reflectance ÷ π L = 12.7 lx × 0.07 ÷ 3.1416 = ~0.28 cd/m2


Example: HPS vs. LEDsExample: HPS vs. LEDs

Unified luminance = 0.2451 cd/m2

Find unified luminance for base case:› 0.28 cd/m2, S/P ratio = 0.65


Example: HPS vs. LEDsExample: HPS vs. LEDsFind the same unified luminance as the base case for the second light source (S/P ratio = 2.15)

~ ~ ~ ~

~0.17 cd/m~0.17 cd/m22 (photopic)(photopic)

~0.245 cd/m~0.245 cd/m22 (unified)(unified)


Example: HPS vs. LEDsExample: HPS vs. LEDs

Both light sources produce the same unified luminance of 0.24 cd/m2:› 0.28 cd/m2 (photopic); S/P = 0.65› 0.17 cd/m2 (photopic); S/P = 2.15

Therefore, the LED system can be dimmed by 40% to produce the same unified luminance.› 0.17 ÷ 0.28 = 0.6

• Option 1: keep same number of LEDs, under-driven• Option 2: reduce the number of LEDs, at nominal power


Example: HPS vs. LEDsExample: HPS vs. LEDsIlluminance (photopic) and power requirements for HPS and LED light sources needed to provide an equivalent unified luminance value of 0.2451 cd/m²Reference: 150 W HPS @ 0.28 cd/m²; 7% reflectance)

*Contribution from 9 pole locations, 18 luminaires total*Contribution from 9 pole locations, 18 luminaires total

110%37440.37060.30LED (2.15)

100%34020.24510.28150W HPS (0.65)

Power(%)

Power*

(W)Unified luminance

(cd/m2)Photopic luminance*

(cd/m2)Light source (S/P ratio)

66%22460.24510.17LED (2.15)

100%34020.24510.28150W HPS (0.65)


SummarySummary

Outdoor lighting› Application efficacy is the total flux within the task area

divided by the effective fixture power• Light where you need it• Reduced light pollution

› Visual efficacy can further reduce power use for high S/P ratio light sources.


MYTHMYTH

High efficacy light sources save energy


Final SummaryFinal Summary

ASSISTASSIST recommends publications1. LED life for general illumination applicationsTesting and evaluating:2. Under-cabinet lighting luminaires3. Directional lighting luminaires4. LED light engines 5. Freezer case lighting luminaires (in preparation)6. Outdoor lighting luminaires (in preparation)

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