Presentation on theme: "Some Fact about LEDs and UV-radiation"— Presentation transcript:
1Some Fact about LEDs and UV-radiation Labino ABAdisa Paulsson M.Sc., Product Development EngineerAugust 2010
2LabinoWe 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
3Topics today Historical development of the power LEDs How LEDs operate Factors influencing the Lifetime and ReliabilityHow to produce the white lightUV LED technology
4What 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 semiconductorInGaN- near UV,blue,greenAlGaN- red, infrared, amber
5LEDs become more and more bright! First power LED was introduced by Philips Lumileds 1999.Luminous flux increased by factor of 2every months!5 mm LEDs,1-2 lmLuxeon I- 5 lm 2002Luxeon III- 50 lm 2006Luxeon Rebel-120 lm, 2010XLamp XM LED delivers efficacy of 160 lm/W (at 350 mA) At 2A, XM LED produce 750 lm at 7W = 60W incandescent light bulb
6Efficiency 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
7More facts about LEDsThe LEDs are not so cold ! !Increasing the power requires more heat to evacuate !!
8Temperature effect on the LEDs! EfficiencyUseful Life
9Temperature effect on the LEDs! Wavelength shift as a function of the temperature
10Lifetime 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 LRCL70 -at least 70 % of the initial lumen outputB50 -50% of population failsB50/L80 or B10/L70All 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 hour life. High quality T5 will loose only 5% at of operation. The main cause of the lumen depreciation is heat generated at LED junction. Most manufacturers of high power white LED estimate 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 hours, then we would expect that hallf of the tested LEDs have lumen maintenance below 70%.B10/L70 at hours
11Lifetime 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 !Source: LED Magazine, 51 news letter, November 2007
12LED Luminaire Lifetime ● Complexity of LED luminaire.● Luminaire reliability is the product of allthe critical components:-in well designed luminaire - the failure should be caused by lumen depreciation
13Quality is a major issue! Performance of the white LEDsThe quality of commercial white LEDs used inlightning products varies widely (26 batches)-A quality assurance is needed to protectconsumers and prevent “market spoiling”Source: Mills E. and A. Jacobson, 2007, Light and Engineering
14Producing the White Light (1) -Color mixing of usually three colors-High efficacy-trade off between luminous efficiency andcolor rendering capability-requires electro-optical devices to control mixing ofdifferent colors-Individual colored LEDs respond differently to drive current,temperature- impact on white light quality1. 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.
15Producing the White Light (2) 1. Phosphor conversion approach (blue or UV-light +phosphor)Broadening of the spectra with phosphor layersGaN 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 systemPhosphor 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.
16What are the Limits of the high power White Light chip? U.S. DOE Forecasted LED Efficacy Improvements, 2009-Difference between cooland warm white origin fromphosphor efficacy.As shown in the figure laboratory LEDs are projected to improve from 160 to 200 lm /W by 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.
17How green are LEDs? Life cycle assessment of Ultra Efficient lamps Source: DEFRA-Department for Environment(UK), 2009
18UV-LED TechnologyWhat 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 spectraUV LED spectra
19UV 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
20UV-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.
21Life time presumption of UV-LED hours life test data-The data exceeds the absolutemaximum rating.
22Measurement of the visible light in UV- light sources 1.Spectral sensitivity curve of the detector2. Fluorescence of the detectorThis 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!
23UV 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 costthe bulb gets very hot+ Relative insensitive to ambient temperatureTechnologies are complementingeach other!
24ConclusionsThe LEDs have a great potential: light waited, high efficiency and low cost products(white).Challenges:Increase power per chipImprove the efficacy of the LEDs specially UV and greenIncrease the product quality and reliabilityIncrease the luminere system efficiency (electronic, optics, heat management)Enhance production process/ Reduce binningReduce environmental impactA new material for UV neededThe 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.
25At 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 expectationsWrong expectations→ Unhappy users100 lm/W LEDs do not make a 100 lm/W light sourcehours lifetime do not make a LED light source with lifetime.