Watt Lumens and LEDs

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copyright © 2010 Lumascape LightingCompany CONFIDENTIAL

Watt Lumens and LEDs

10 April 2011

Cameron Spiller - Senior Industrial Designer

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Agenda

Myths surrounding LEDsWhat can effect the Efficacy and Reliability of an LED Luminaire?Thermal managementCreative marketing Losses within an LED system Philips Fortimo, something for nothing?Hot Cold Performance of LEDsCreating Colour with LEDsLEDs – Absolute or Relative PhotometrySelecting an LED based Luminaire

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Myths surrounding LEDs

Higher Watts = more light and a superior fittingLEDs last for 100,000 hrs or even foreverWhen LEDs fail, they just go outLEDs are a cool light source and produce no heat This product uses a reputable quality LEDs. That is all that matters, therefore it must be a good product

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What can effect the Efficacy and Reliability of an LED Luminaire?

LED choiceManufacturer, type of LED, Flux Bin, Forward Voltage Bin, ColourUnderstanding LED technology and ability to “translate” manufacturers’ data to the real world

Drivers, dimmers, controllersOften overlooked, effects life and efficacy of an LED luminaireSome drivers for particular applications are only 50% efficient

OpticsMisunderstood, always overlooked, effects efficacy of an LED luminaireLosses, glare, wasted light – proper selection is crucial

Thermal managementThermal managementThermal management

AND

Thermal management!

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Why thermal management?

LEDs generate heatAllowing excess heat to build up directly and dramatically affects both short term and long term LED performanceShort term – colour shift, reduced light outputLong term – accelerated lumen depreciation and thus shortened useful life

Thermal management is the single most important aspect of design for reliability

LED "drop-in" replacements such as MR-16 replacements and fluorescent type LED lamp replacements, are in theory designed to provide the necessary heat sinking for the LEDs when installed in open Luminaires. However when installed in luminairesnot specifically designed with the proper thermal management of this type of LED module in mind, good thermal management will be unlikely

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Creative marketing

Manufacturer A

This is not how this fixture will operate!

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Creative marketing

Manufacturer A

LED manufacturers test their products for luminous flux and colour based on a 15-20 millisecond power pulse, at a fixed Tj of 25°C.With a good thermal design Tj is typically between 80°C and 100°C or greater at room temperature.Therefore white LEDs will provide at least 10% less light than the manufacturer's rating, and the reduction in light output for products with inadequate thermal design can be significantly higher.

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Creative marketing

Manufacturer B

US Department of Energy – Case Study

Continuous operation at elevated temperature dramatically accelerates lumen depreciation resulting in shortened useful life. Experiment was done with two identical LEDs driven at the same current but with an 11°C difference in Tj. Estimated useful life (defined as 70% of initial lumen output) decreased from ~37,000 hours to ~16,000 hours, a 57% reduction, with the 11°C temperature increase.

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Creative marketing – Actual Lumen Maintenance

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Creative Marketing – Actual Lumen Maintenance

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Creative marketing

Manufacturer C

Source: US Department of Energy

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Example of losses through an LED system

Drive Current and it’s effect on LED performance

Heat and it’s effect on LED performance

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Philips Fortimo – Something for Nothing?

Wattage: 34 WFlux: 378.6 lmEfficacy 11.13 lm/WFe: 10.54 W

Wattage: 33.77 WFlux: 2193 lmEfficacy 64.92 lm/WFe: 6.937 W

Fortimo Without Conversion Filter

Fortimo With Additional Conversion Filter

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LEDs – Absolute or Relative Photometry

Due to significantly different thermal conditions various LED types when measured outside the luminaire, are likely to produce very different light output characteristics then when coupled to the fixture.

Thermal conditions within the luminaire significantly affect the LED light output, relative photometry can not be used as an accurate method to test LED luminaire performance

Extrapolating results from the raw LED data can be very inaccurate and misleading.

A common way of testing bare LEDs without a luminaire is with the junction or thermal pad temperature set to 25°C.

The advantage of absolute testing for LED luminaires is that the report presents true performance of a complete LED luminaire.

This is very important, as the performance of an LED luminaire greatly depends on:LED technology,LED binning,applied current, as well as thermal management characteristics.

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LEDs – Absolute or Relative Photometry … cont’d

The data from various luminaire manufacturers is still presented in various formats

They often including pro rata results scaled from bare LED data

Difficult to compare the true performance of LED luminaires

To overcome this issue, the Illumination Engineering Society of North America (IESNA) has developed:

Approved Method for Measuring Lumen Maintenance of LED Light Sources (LM-80)Approved Method for Electrical and Photometric Measurements of Solid-State Lighting (LM-79).

In the absence of an equivalent international standard LM79 and LM80 have become the default standard to test to. I understand the CIE currently have a draft standard and we look forward to seeing it.

Switching to absolute photometry is one of the fundamental changes in photometric test procedures introduced with LED sources.

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LM-80 … cont’d

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The graph shows the lumen degradation for one of the LEDs currently available in the market as a function of the temperature of an appropriately coupled thermal pad. The graph shows that if the thermal pad temperature increases to 125°C, the LED light output reduces by more than 20%.

Source: Philips Data Sheet DS63www.philipslumileds.com/uploads/20/DS63-pdf

Thermal management – lumen degradation?

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What is Junction Temperature (Tj)?

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Thermal management - Hot Cold Performance of LEDs

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Thermal Effect on LED Efficacy

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10

20

30

40

50

60

70

80

90

85ºC 100ºC 120ºC

LED Case Temperature

lm/W

Sample 1 - 350mA (3.16W)

Sample 1 - 700mA (6.88W)

Sample 1 - 1000mA (10.38W)

Sample 2 - 350mA (3.01W)

Sample 2 - 700mA (6.56W)

Sample 2 - 1000mA (9.98W)

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Thermal Effect on LED Flux

0

100

200

300

400

500

600

85ºC 100ºC 120ºC


lm

Sample 1 - 350mA (3.16W)

Sample 1 - 700mA (6.88W)

Sample 1 - 1000mA (10.38W)

Sample 2 - 350mA (3.01W)

Sample 2 - 700mA (6.56W)

Sample 2 - 1000mA (9.98W)

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Thermal Effect CCT (K)

2600

2700

2800

2900

3000

3100

3200

3300

3400

3500

85ºC 100ºC 120ºC


CC

T (K

)

Sample 1 - 350mA (3.16W)

Sample 1 - 700mA (6.88W)

Sample 1 - 1000mA (10.38W)

Sample 2 - 350mA (3.01W)

Sample 2 - 700mA (6.56W)

Sample 2 - 1000mA (9.98W)

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Thermal Management Binning at 25ºC vs 85ºC

On 18 February 2011, Lumileds announced the release of a new Luxeon Rebel LED. They will be characterising it’s typical performance at 85ºC, not the industry standard 25 ºCCree were not far behind and have announced that they too will be characterising some of their LEDs at a junction temperature of 85ºC also.This is a huge step forward in the publication of honest easy to understand LED data.

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Thermal Management - Development

Centria LED Spotlight

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Photometric Testing1500mm Integrating Sphere

For testing the luminous flux of various types of lamps and smaller luminaires Also for single or multiple LED arrays

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Photometric Testing

300mm Integrating SphereDesigned specifically to test and evaluate single LED and very small LED arrays.

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Incremental drive current testing - Sample .1. (LRW)

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Incremental drive current testing - Current Droop - Sample .1.

Sample 1700mA: 15% Drop1000mA: 27% Drop

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Incremental drive current testing - Current Droop - Sample .1.

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Incremental drive current testing - Current Droop - Other Various Samples.


Sample 3700mA: 21% Reduction1000mA: 37% Reduction


Sample 5700mA: 21% Reduction1000mA: 36% Reduction

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Creating Colour with LEDs

Wattage: 19.66WFlux: 217.4 lmEfficacy ll.06 lm/WFe: 1.238W

MR16 Halogen Inside Luminaire

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Wattage: 19.75 WFlux: 45.55 lmEfficacy 2.31 lm/WFe: 0.733W

Drive Current: 350mAWattage: 1.05 WFlux: 39 lmEfficacy 37.1 lm/WFe: 0.284 W

MR16 Halogen with Red Dichroic Filter

Red LED (Pulse Tested)

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Losses

37.5% Loss

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Wattage: 19.75 WFlux: 45.55 lmEfficacy 2.31 lm/WFe: 0.733W

Drive Current: 350mAWattage: 1.05 WFlux: 39 lmEfficacy 37.1 lm/WFe: 0.284 WDelivered Flux: 24.4lm (assuming 37.5% loss)Actual Efficacy: 23.2lm/W (assuming 37.5% loss)

MR16 Halogen with Red Dichroic Filter

Red LED (Pulse Tested)

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Wattage: 19.84WFlux: 105.5 lmEfficacy 5.32 lm/WFe: 0.611W

Drive Current: 350mAWattage: 1.15WFlux: 100.4 lmEfficacy 87.3 lm/WFe: 0.194WDelivered Flux: 62.75lm (assuming 37.5% loss)Actual Efficacy: 54.6lm/W (assuming 37.5% loss)

MR16 Halogen with Green Dichroic Filter

Green LED (Pulse Tested)

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Wattage: 19.95WFlux: 25.32 lmEfficacy 1.27 lm/WFe: 0.555W

Drive Current: 350mAWattage: 1.34 WFlux: 37.84 lmEfficacy 28.2 lm/WFe: 0.365WDelivered Flux: 23.65lm (assuming 37.5% loss)Actual Efficacy: 17.6lm/W (assuming 37.5% loss)

MR16 Halogen with Blue Dichroic Filter

Blue LED (Pulse Tested)

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Things to consider when selecting an LED based Luminaire

Has it been tested in accordance with IESNA LM-79-08 test procedure or equivalentHas the manufacturer tested the performance of the actual product? Or are their performance claims based on extrapolations from LED datasheets?Ask about warrantyCheck ingress protection (IP) ratings, and choose an appropriate rating for the intended applicationAsk for operating temperature information and how this data relates to luminaire efficacy and lumen depreciationCheck colour temperature for suitability in the intended applicationAssess glare, preferably with the luminaire at intended mounting height and under typical night time viewing conditions, compared to incumbent technologyEvaluate economic payback, based on applicable energy, equipment, maintenance, and control costs for the site

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- 20 x 6W 4000 °K (LS321LED)- 8 x 3W 4000 °K (LS151LED)- 2 x 20W 4000 °K (LS853LED)

Total 220 watts !!(Including Powersupplies)

- 20 x 50W MR16 (LS321A) - 8 x 20W MR16 (LS381A)- 2 x 20W Metal Halide (LS843)

Total 1320 watts(Including Transformers)

Standard Halogen / Metal Halide

LEDscape LED

Energy, Cost and Maintenance Comparisons

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Energy, Cost and Maintenance Comparisons

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Why Comparing by LED Luminaires by Wattage Does Not Work

Comparing LED Luminaires by their Wattage alone does not take into account:Loss due to Glass TransmissionLoss due to Mechanical Hardware and Glare ControlLoss due to OpticsLoss due to Drive Current effect on the LEDsLoss due to Thermal Effect on LED – thermal managementLoss due to LED driver efficienciesEfficiency of different Brands of LED

Even models within the same brandEven colour and flux bins within the same model within the same brand!

Efficiency of various LED colours and colour temperatures

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How to compare - What to look for?

Who is the Manufacturer? Do they have the capacity to develop thermal management systems and to test LED products properly?Have they tested in accordance with the standards?Read and understand the datasheet! How many lumens / watt does the luminaire produce? Stabilised!How has the manufacturer dealt with the heat produced by the LED?Does the manufacturer use a reputable brand LED?So the LED has been thermally managed and will last 50,000 hrs, how long will the supporting LED driver last? Functional LEDs are not much good if the driver fails.Under what conditions was the product tested? Are they similar to your installation? Can the manufacturer tell you the junction temperature and the test conditions?Does the product include any type of glare control?What is the colour temperature and CRI? The data sheet said up to 80lm/W, how many lm/W can you expect from the configuration that suits your purpose?

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In Conclusion

Selecting an LED luminarie requires careful product selectionWell designed glare control should not effect the useful beam, but it will reduce the apparent efficiencyInadequate design of drivers, optics, thermal management results in reduced luminaire life, reduced light output, colour shift and un-acceptable levels of glareElectronic drivers / controllers are often the forgotten weak linkLEDs are an extremely accessible technology with little barrier to entry. Unfortunately this means that almost anyone can produce an LED based product, without the required depth of knowledge to design and test, Differences between the performance of Luminaires can be significant, with many examples of Luminaires consuming less power and producing more light than their competitors.Specifying by wattage doesn’t mean a better end result, unless you have shares in Energex.

Watt Lumens and LEDs

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