LED Reliability: Color Shifts

[Dana Riddle]

Been very busy for the last few months. Things are finally beginning to settle down, and I hope to be able to participate more on R2R.
Here's a paper that discusses factors that can cause color shifts in LEDs. Although the gist examines effects on LEDs producing 'white' light, some factors are applicable to monochromatic LEDs. Many thanks to Jack Kent (founder of Kent Marine) for getting this paper to my attention.

https://www.energy.gov/sites/prod/files/2017/04/f34/lsrc_colorshift_apr2017.pdf

 

[oreo54]

Been very busy for the last few months. Things are finally beginning to settle down, and I hope to be able to participate more on R2R.
Here's a paper that discusses factors that can cause color shifts in LEDs. Although the gist examines effects on LEDs producing 'white' light, some factors are applicable to monochromatic LEDs. Many thanks to Jack Kent (founder of Kent Marine) for getting this paper to my attention.

https://www.energy.gov/sites/prod/files/2017/04/f34/lsrc_colorshift_apr2017.pdf

Might as well add a paper on "colored" LEDs

https://www.energy.gov/sites/prod/files/2019/01/f58/ssl_rti_lm80-color-leds_july2018.pdf

This report provides the results of an analysis of the LM-80-15 data for select commercial color LED products.This analysis was performed only on color LEDs in high-power packages. Because the HP-LED package in general exhibits minimal package-related changes in luminous flux and chromaticity, the performance benchmarked during this analysis likely proves to be a good snapshot of the performance of color LEDs.Other packaging formats, such as polymer-based MP-LED packages, may exhibit lower performance, especially for violet and deep blue colors operated at high forward currents and Tj, because of photo-oxidation of the polymer resin used in these packages

For the more efficient colors made from InGaNand AlGaInP LEDs(e.g., royal blue, red), the chromaticity maintenance was high,and the overall chromaticity shift was minimal.

Update

DOE publishes research on LED lumen and chromaticity maintenance or shift

Studying different package types, RTI International and LED Lighting Advisors found different aging characteristics of components yet a general improvement in LED quality.

www.ledsmagazine.com

Lumen and Chromaticity Maintenance Behavior of LED Packages Based on LM-80 Data

A report that assessed four major LED package platforms used in SSL applications for luminous flux and chromaticity maintenance by analyzing data sets

www.energy.gov

The new research found that lumen maintenance performance is generally greatly improved across all package types so long as SSL system designs are accomplished cognizant of LED manufacturer guidelines. The data reveals that 96% of the components deliver L70 lumen maintenance (70% or more of initial lumen output) for more than 60,000 hours. There are of course caveats. Generally, mid-power LEDs must be driven at less than 200 mA to achieve such lifetime. Both high-power and COB LEDs can be driven reliably to 1.5A. And for CSP LEDs the key is temperature. The system design must keep junction temperature to 120°C or less.

This analysis, which is an update of an earlier study completed in 2015 that focused on only luminous flux maintenance, demonstrated that there has been continued improvement across all LED package types. In total, 96% of the αvalues in this study are less than 6 × 10-6 which corresponds to an L70 time of nearly 60,000 hours (hrs). Perhaps the largest gains have occurred in polymer-based packages where better materials have resulted in marked improvements in luminous flux maintenance to where the performance of polymer-based packages is nearly the same as that of ceramic-based packages for If≤ 200 milliamperes ( mA). The current handling capabilities of COB and ceramic-based packages have also improved significantly, and these package platforms exhibit excellent luminous flux maintenance at operational currents of 1,500 mA and higher. The newly introduced CSP LEDs are shown to exhibit luminous flux maintenance values in line with the other package platforms, especially at operational temperatures of 120 degrees Celsius (°C) and lower and operational currents of 700 mA and lower

 

[blasterman]

Basically as long as you conform to the LED makers thermal guidelines in regards to T/c case temp the fixture will last a long time. Uh...yeah?

The phosphors used in LEDs have improved dramatically in terms of thermal degradation over the past 6 years. Color shift is next to a non issue. Even the Chinese are getting better as they rip off designs.

The biggest offenders I've seen are Reef PAR 38 bulbs. Ive seen some that get too hot to touch, and that's the outside.

High current LED platforms are rapidly being replaced by more distributed LED architectures that dont need chunky heat sinks and active cooling. Some of these are up to 2k lumen per linear foot and higher. Thats impressive for no cooling other than PCB board. Sad they won't make blue versions for the reef industry.

 

[Brian_68]

Following the thermal guidelines costs time and money for the PC board and heat sinks so one cannot assume all the manufacturers are doing it without taking temps and measuring currents. Often the manufacturers design guidelines are borderline unrealistic in practice.