2Lumen Maintenance Definition Definition: change in light output of a light source over operational life, relative to initially measured light outputLxx = time to xx% of original light outputL70 = time to 70% of original light outputL50 = time to 50% of original light outputpg. 2
350,000 Hours Is Trivia Point: 50,000 hours is: 137 Years at 1 hour/day 68.5 Years at 2 hours/day34.2 Years at 4 hours/day22.8 Years at 6 hours/day17.1 Years at 8 hours/day11.4 Years at 12 hours/day5.7 Years at 24 hours/daypg. 3
4LED Lumen Maintenance History 1990’s LEDs used for traffic signals and exit signs. First basic studies on LED lifetime performed.< LEDs were used as indicators. Lifetime did not matter too much.Lumileds (Philips) introduces first High Power LED. Lifetime testing gets more serious.2004 LRC/ASSIST publishes first work on the topic. Basic science understood.2006 LRC/ASSIST publishes ASSIST recommends test procedure for lifetime testing of High Power LEDs, which becomes the basis for IESNA LM standard2007 Philips Lumileds publishes white paper, extending the knowledge of the industry on the topic (IF)2008 IES LM is published2009 Cree publishes reliability white paper (TAIR)
5LED Lumen Maintenance Critical Parameters 1. TAIRAmbient Air Temperature2. TJJunction Temperature3. TSP / TC / TSSolder-Point Temperature / Case Temperature4. IFForward Current /Drive Current
6Cree Lumen Maintenance Model Degradation in first 5,000 hours is mostly due to degradation in the silicone encapsulant.After 5,000 hours, this mechanism drops out and the slower chip degradation dominates.Good quality LEDs in well-designed fixtures will last for decades under normal use and operating conditions.
7L70 Lifetime Prediction – IF = 350 mA How Do You Know They Last >50,000 Hours?
1340,000 Hour / 4.5 Year XLamp Long-Term Data Low temp (25ºC) testing is a good surrogate for the LED chip depreciation – TJ = 65ºCAt lower ambient air temperature, LEDs hardly depreciate at all.pg. 13
14System Lifetime is What Counts System Lifetime is What Creates ValueHeat Sink: Linchpin of the entire system. If this is poorly designed, all the other components can be compromisedDriver: Much improvement on rel and performance especially with the large suppliers.LED Lamps: Practically never fail; depreciate very slowly in a well-designed systemOptical Components: Can (rarely) yellow over time and lose light; system design choice
16What is LED binning?Used to define similar groups of parts by performance characteristicsNot unlike other industries that bin based on performance, ie: microprocessorCree XLamp® LED binning based on two parameters:Flux (total light output)Chromaticity (white), Dominant wavelength (color)Even fluorescent tubes are binned by chromaticity“daylight”, “warm white”, etc.
17Two Main Types of Binning •Chromaticity or Color Binning–Some defined “Box” in thewhite area on or near theBlack Body Locus (White LEDs)–Dominant Wavelength (Color LEDs)•Brightness or Flux Binning–Minimum luminous flux or radiant Flux–Bin sizes (flux range)varies by supplier
18Brightness or Flux Binning Flux = total light emitted in all directions Measured using an integrating sphere
19Luminous Flux Binning LEDs are tested & sorted into luminous flux bins Performance binning is very standard in the semiconductor industry (e.g., CPUs), but confusing to the lighting industry where performance is very standardizedDriver 350 mAFlux:102.3 lm
20Chromaticity BinningCCy: 0.35CCx: 0.32Driver 350 mA
21Design & Specification Strategies Strategy #1Understand light, binning, and your application needsDo the mixing yourself in your fixture if the application will allow itSave moneyStrategy #2Insist on the tightest bin availablePay the highest price possible
22Design & Specification Strategies Let Cree do the mixing for you...EasyWhite™Consistent colorNo complicated mixing recipesReduced inventoryEase of manufacturingStrategy #3