Whatever happened to LED "droop"? - Page 1
Forum section: electronics / general

author: Analog Kid
author_rank: Super Contributor
timestamp: August 08, 2025, 07:29:29 pm
content: Back in the 20-ought-10s, I remember reading a lot about the phenomenon of LED "droop", which caused the efficiency of LEDs to drop precipitously as the current through the device increased.Articles like this onewere all over the place.So what happened? Was this problem finally solved? I don't remember seeing anything celebrating the victory over this pitfall.

author: thm_w
author_rank: Super Contributor
timestamp: August 08, 2025, 10:21:10 pm
content: Looks like its less of an issue now?https://www.digikey.ca/en/products/detail/ams-osram-usa-inc/GW-Q9LR33-PM-M5N3-XX53-1-180-R18/16731011https://www.digikey.ca/en/products/detail/cree-led/JB3030CWT-E-B65EA0000-NZ000001/22162305There is still a drop due to temperature.

author: wraper
author_rank: Unknown
timestamp: August 08, 2025, 10:27:43 pm
content: It might be not as bad as with older LEDs but efficiency is still significantly dependent on current that is pushed through them, especially closer towards the max current. The graph above does not tell the full story as the Vf rises with current as well and as you should know P=V*I.From the datasheet linked above

author: thm_w
author_rank: Super Contributor
timestamp: August 08, 2025, 10:37:29 pm
content: Yeah I think that first one is multi-chip and the second one might be a large die, and they stay in the linear region on the graph as you show.Quotehttps://www.sciencedaily.com/releases/2024/11/241125125828.htmQuotehttps://www.caltech.edu/about/news/microscopic-origin-efficiency-droop-leds-80436

author: amyk
author_rank: Super Contributor
timestamp: August 09, 2025, 04:00:49 am
content: Also related:https://www.eevblog.com/forum/chat/the-dubai-lamp/Everywhere else, companies prefer to drive LEDs as hard as they can so they'll fail sooner.

author: Psi
author_rank: Super Contributor
timestamp: August 09, 2025, 04:36:15 am
content: Quote from: amyk on August 09, 2025, 04:00:49 amYep, this is so true.If you hack/DIY the brightness on off-the-shelf led lighting products to you will significantly extend the lifespan.Often from a few years to a few 10's of years. It's usually not the LED that die, however they dim with age and shift color, it's usually all the heat slowly cooking caps or the bridge rectifier diodes that make them die.It's the main reason i am in the process of converting all house lighting to recessed LED strip. It spreads the heating over a wide area so each LED runs cool and it separates the powersupply from the lighting for easy replacement if needed. Also looks cool and easy to do dimming and add into home automation systems.

author: Analog Kid
author_rank: Super Contributor
timestamp: August 09, 2025, 05:30:15 am
content: So it sounds like the upshot is that they never really solved droop: is that true? Because I haven't heard anything about it for ... years now.Instead of larger LED elements that are more inefficient because they draw more current, are manufacturers now using multiple smaller elements to get around the problem?

author: Siwastaja
author_rank: Super Contributor
timestamp: August 09, 2025, 07:46:33 am
content: I hear this "droop" terminology the first time now!The photons-emitted-per-charge drop with increasing current phenomenon was always there, and is still there - maybe some modern LEDs are "better" than some of their older counterparts, but the phenomenon has not disappeared.Note that differences between products were always large, and will continue to be. And one obvious way for a manufacturer to affect this relationship is simply by the amount of "derating" they choose to apply: if manufacturer aims for maximum possible current specification (just barely achievable) then the curve is going to look less of a straight line. If another manufacturer decides they want their LEDs to show good efficiency overall, they can just sell otherwise ideal part specified for less maximum current and thus the most non-linear extreme end of the curve cut off.

author: AVGresponding
author_rank: Super Contributor
timestamp: August 09, 2025, 08:49:56 am
content: Even if driven sensibly, modern phosphor type LEDs degrade over time anyway (or at least, the phosphor and the resin it's encapsulated within does), resulting in colour change and dimming.

author: tom66
author_rank: Super Contributor
timestamp: August 09, 2025, 10:36:52 am
content: I have heard the effect is not related to current directly, but instead the temperature of the device increasing reduces efficiency. I do not know the reason why, possibly a similar effect to normal forward voltage of diodes dropping with increasing temperature, or something like how solar panels are also less efficient when hotter.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2025, 12:04:57 pm
content: Going from the rough tests I performed awhile ago on testing LEDs with short, high current pulses, it's efficiency does reduce at higher current densities, so it's not due to temperature rise. This will always be a problem to some extent, as long as there's a resistive element in the LED, because ohmic losses always increase by the square of the current, not linearly: P = I2R.

author: Analog Kid
author_rank: Super Contributor
timestamp: August 09, 2025, 07:30:22 pm
content: Quote from: Zero999 on August 09, 2025, 12:04:57 pmThat's interesting.In a related matter, I've built a lot of "Joule thieves", very bright LED flashlights using a blocking oscillator to drive them from a 1.5 volt cell. I've been doing this for many years, and all of them still work as well as they did when built.When I ran a simulation in LTSpice, I got the following current graph:They're obviously being massively overdriven for very short times. But it doesn't seem to harm them at all. (I've never actually measured the current, but I'm trusting that the simulation was at least in the ballpark.)

author: ejeffrey
author_rank: Super Contributor
timestamp: August 09, 2025, 08:04:07 pm
content: One obvious possibility is that the cost per mm^2 of die area has gone _way_ down. This may lead to less pressure to run at the absolute maximum current density.There have also been improvements in the efficiency of getting the photons out. The index of refraction of GaN is quite high and total internal reflection and light trapping are serious problems. Any light which doesn't escape is more heat, and more need to drive even harder to get a usable quantity of light.

author: cunningfellow
author_rank: Regular Contributor
timestamp: August 11, 2025, 10:19:49 pm
content: They have little blue pills for it now

author: ajb
author_rank: Super Contributor
timestamp: August 12, 2025, 06:30:23 pm
content: In general, yes, efficacy drops off with increasing power. At a basic level you have more losses due to increased I2R losses (which affects external connections, but also bond wires), higher bulk resistivity at increased temperatures. As already noted, the forward voltage increases with increased current, which is a basic diode property, so power increases at a slightly elevated rate versus current. Most LEDs have a negative efficacy tempco as well, so that is a factor if current is increased without additional cooling, but blue LEDs may have apositiveefficacy tempco. White LEDs (and other PC colors) have the phosphor to consider, which seems to be a significant factor -- if you look at the parts that claim really high efficacy (like 200lm/W), they are always parts with a relatively large light emitting surface, suggesting that power density in the phosphor is probably a big factor.