Some Fact about LEDs and UV-radiation

Labino ABAdisa Paulsson M.Sc., Product Development Engineer

August 2010

Labino• We develop and manufacture the UV and white light

lamps for industry and public sector.• The lamps are based on MPXL and LED technology.• Founded 1994, Sweden

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Topics today

• Historical development of the power LEDs• How LEDs operate• Factors influencing the Lifetime and Reliability• How to produce the white light• UV LED technology

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What are the LEDs?

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Electroluminescence!

InGaN- near UV,blue,green

AlGaN- red, infrared, amber

-Electroluminescence was discovered in 1907

-first LED was reported in 1927, by Oleg Losev

-LEDs are semiconductor which emits the photons when current is passing trough the material

-Color = energy gap of the semiconductor

LEDs become more and more bright!

XLamp XM LED delivers efficacy of 160 lm/W (at 350 mA)

At 2A, XM LED produce 750 lm at 7W = 60W incandescent light bulb

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Luxeon I- 5 lm 2002 Luxeon III- 50 lm 2006 Luxeon Rebel-120 lm, 2010Luminous flux increased by factor of 2

every 18-24 months!

First power LED was introduced by Philips Lumileds 1999.

5 mm LEDs,1-2 lm

Efficiency is increasing

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• Approaching 2010: Luminous efficiency 160 lm/ W phosphor white power LEDs

•Expect ~ 200 lm/W power LED performance within the next 3-5 years

More facts about LEDs

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The LEDs are not so cold ! !

Increasing the power requires more heat to evacuate !!

Temperature effect on the LEDs!

Efficiency

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Useful Life

Temperature effect on the LEDs!

Wavelength shift as a function of the temperature

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Lifetime of LEDs

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How to define the useful lifetime of the LEDs? Lumen maintenance or Lumen depreciation!

L70 -at least 70 % of the initial lumen output

B50/L80 or B10/L70

B50 -50% of population fails

LM-80 test criteria developed by U.S. Department of Energy and LRC

B10/L70 at 60 000 hours

Lifetime of LEDs

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Source: LED Magazine, 51 news letter, November 2007

1. Drive current2. Temperature internal and ambient

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LED Luminaire Lifetime

● Complexity of LED luminaire.

● Luminaire reliability is the product of all

the critical components:

-in well designed luminaire - the failure should be caused by lumen depreciation

Quality is a major issue!

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-The quality of commercial white LEDs used in

lightning products varies widely (26 batches)

-A quality assurance is needed to protect

consumers and prevent “market spoiling”

Source: Mills E. and A. Jacobson, 2007, Light and Engineering

Performance of the white LEDs

Producing the White Light (1)

1. Color-mixing LEDs (RGB method)

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-Color mixing of usually three colors

-High efficacy

-trade off between luminous efficiency and

color rendering capability

-requires electro-optical devices to control mixing of

different colors

-Individual colored LEDs respond differently to drive current,

temperature- impact on white light quality

Producing the White Light (2)

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1. Phosphor conversion approach (blue or UV-light +phosphor)

-the most common method blue LED + Phosphor

-UV phosphor coated LEDs –less efficient,

better color rendering

- low conversion efficiency

-A lot of research to improve phosphor coating quality and efficacy

-More simple and not so costly production compared to RGB system

GaN or InGaN LEDBroadening of the spectra with phosphor layers

What are the Limits of the high power White Light chip?

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U.S. DOE Forecasted LED Efficacy Improvements, 2009

-Difference between cool

and warm white origin from

phosphor efficacy.

How green are LEDs?

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Life cycle assessment of Ultra Efficient lamps

Source: DEFRA-Department for Environment(UK), 2009

UV-LED Technology

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What is the main difference between UV LED and traditional UV light source?

UV LED spectraXe spectra

No UVB!

UV LED Technology

UV LED also emits a small amount of the visible light mostly blue-violet in spectral range 380nm to 475nm.

The peak wavelength

is at 365 nm

blue LED, InGaN

UV-LED and White Light

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How to solve this technology insufficiency?

White Light Block Filter!

The visible light (380nm-780) in UV sources-bad for many applications!

Life time presumption of UV-LED

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- 6000 hours life test data

-The data exceeds the absolute

maximum rating.

Measurement of the visible light in UV- light sources

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1.Spectral sensitivity curve of the detector

2. Fluorescence of the detector

High transmittance in visible area!

UV LED versus MPXL

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+light weighted and small

+good efficiency

+robust

+long life

+Intensity: 0.3 W of UVA radiation

-High cost of lm/W compared to MPXL

+Cold (no IR)

-sensitive to high ambient temperature

-Lack of standard optical solutions

-Problem with white light leakage-requires filter

-require active or passive cooling solution

-Big and clumsy

+high efficiency

+keeps running after drop

+lifetime up to 4000 hours

+ high intensity: 5 W of UVA radiation

+relatively low cost -the bulb gets very hot

+ Relative insensitive to ambient temperature

MPXLUV-LED

Technologies are complementing

each other!

Conclusions

• The LEDs have a great potential: light waited, high efficiency and low cost products(white).

• Challenges:– Increase power per chip– Improve the efficacy of the LEDs specially UV and green– Increase the product quality and reliability– Increase the luminere system efficiency (electronic, optics, heat management)– Enhance production process/ Reduce binning– Reduce environmental impact– A new material for UV needed

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• Who truly wants to unleash the potential of LED technology should not only seize the opportunities, but also bear some of the responsibilities.

False or incomplete information → wrong expectations

Wrong expectations→ Unhappy users

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At Last LEDs….

100 lm/W LEDs do not make a 100 lm/W light source

50 000 hours lifetime do not make a LED light source with 50 000 lifetime.

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Thank you!

Labino AB

Stockholm | Sweden