Some Fact about LEDs and UV-radiation Labino AB Adisa 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

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

What are the LEDs? Electroluminescence! InGaN- near UV,blue,green -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 InGaN- near UV,blue,green AlGaN- red, infrared, amber

LEDs become more and more bright! First power LED was introduced by Philips Lumileds 1999. Luminous flux increased by factor of 2 every 18-24 months! 5 mm LEDs,1-2 lm Luxeon I- 5 lm 2002 Luxeon III- 50 lm 2006 Luxeon Rebel-120 lm, 2010 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

Efficiency is increasing Evolution of LED efficiency. The latest press release from Cree was that they have white power LED which produces 208 lm/W at 350mA. This is result of improvements in blue optical power, lower operating voltage and higher conversion efficiency. • 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 The LEDs are not so cold ! ! Increasing the power requires more heat to evacuate !!

Temperature effect on the LEDs! Efficiency Useful Life

Temperature effect on the LEDs! Wavelength shift as a function of the temperature

Lifetime of LEDs How to define the useful lifetime of the LEDs? Lumen maintenance or Lumen depreciation! LM-80 test criteria developed by U.S. Department of Energy and LRC L70 -at least 70 % of the initial lumen output B50 -50% of population fails B50/L80 or B10/L70 All lamp types declines with operating time. Power LEDs behave differently compared to the traditional light sources. They rarely failed completely but instead their light output degrades gradually. .  Since the human eye generally can’t detect a change in light output until there has been 30% depreciation, L70 is often established as the target for an application. Compact fluorescent lamps los more than 20% of their initial lumens during 10 000 hour life. High quality T5 will loose only 5% at 20 000 of operation. The main cause of the lumen depreciation is heat generated at LED junction. Most manufacturers of high power white LED estimate 30 000 hours at 350 mA and maintaining Tj below 90C. The real life time testing is impractical so there is some testing procedure for LED product. They are tested during 6000 hour and values are extrapolated. If the LEDs are rated for B50/L70 at 50 000 hours, then we would expect that hallf of the tested LEDs have lumen maintenance below 70%. B10/L70 at 60 000 hours

Lifetime of LEDs 2. Temperature internal and ambient 1. Drive current The life time of the LED is seriously affected by two factors: one is drive current (how much power you supply to device; and the other is temperature. Higher Current cause the die temperature to increase. A Efficiency drops rapidly with increasing current or Tj. Good thermal management is required. Postulated life time is 50 000! Source: LED Magazine, 51 news letter, November 2007

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! Performance of the white LEDs 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

Producing the White Light (1) -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 1. Color-mixing LEDs (RGB method) Disadvantages of color mixing method: Each color respond differently to drive current, operating temperature. Requires electro-optical devices for blending and diffusion of different colors. Phosphor conversion: difficulties to maintaining the consistent quality of the white light due to natural variations in blue and UV-LEDs.

Producing the White Light (2) 1. Phosphor conversion approach (blue or UV-light +phosphor) Broadening of the spectra with phosphor layers GaN or InGaN LED -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 Phosphor conversion: difficulties to maintaining the quality of the white light due to natural variations in blue and UV-LEDs. Phosphor based LEDs have lower efficiency due to Stokes loss which means due to conversion of blue light to higher wavelengths of the visible light. Much research is going on how increase the efficacy and quality of produced white light.

What are the Limits of the high power White Light chip? U.S. DOE Forecasted LED Efficacy Improvements, 2009 -Difference between cool and warm white origin from phosphor efficacy. As shown in the figure laboratory LEDs are projected to improve from 160 to 200 lm /W by 2014. Commercial production is lower but following equally the trends. Supply chain issues (like volume production, line quality control..) prevent the commercialized lamps from ever achieving the laboratory efficiency levels.

How green are LEDs? Life cycle assessment of Ultra Efficient lamps   Source: DEFRA-Department for Environment(UK), 2009

UV-LED Technology What is the main difference between UV LED and traditional UV light source? No UVB! There have been done some research to use UVA LED with peak at 365 nm for a water sterilization. The results are promising. UVA radiation was able to inactivate the bacteria. There is many advantages with UV LED compared to traditional UV lamps. Xe spectra UV LED spectra

UV LED Technology blue LED, InGaN The peak wavelength is at 365 nm UV LED also emits a small amount of the visible light mostly blue-violet in spectral range 380nm to 475nm. Although Labino has the highest quality and the most efficient UV- LEDs available at the market there are some problems connected to blue light leakage from the UV LEDs. For the moment we don't really have other material with large gap in order to get directly UV radiation. The Zinc Oxyde is a promising solution but it is far from be commercial product for LEDs... blue LED, InGaN

UV-LED and White Light How to solve this technology insufficiency? The visible light (380nm-780) in UV sources-bad for many applications! White Light Block Filter! How to solve this technology insufficiency? To compensate for UV- LED technology insufficiency we designed a white block filter which simply cuts off the visible light of the spectra.

Life time presumption of UV-LED - 6000 hours life test data -The data exceeds the absolute maximum rating.

Measurement of the visible light in UV- light sources 1.Spectral sensitivity curve of the detector 2. Fluorescence of the detector This is a sensitivity curve of the silicon photodiode of one typical visible light meter Luxmeter. These kind of meters are not accurate in measuring blue light. Accurancy of the measurement is given for the central part of the sensitivity curve. The error in measured value can be 50% or more. Only solution is to use more advanced equipment , spectrophotometers and measure luminance for each wavelength. Second problem when measuring the white light is fluerescence of detector, very common phenomena. The fluorescence of the detecting sensor increases the amount of detected visible light We recommend using of UV block filter which prevent the fluorescence and which is transparent for visible light. High transmittance in visible area!

UV LED versus MPXL UV-LED MPXL Technologies are complementing +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 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 The removing heat from the lamp is a real challenge. For the present there is not material which can produce the UV-LEDs (365nm) with high efficacy.

At Last LEDs…. 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 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.

Thank you! Labino AB Stockholm | Sweden