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TL;DR - based on the physics of LEDs, does current or power give a better estimation of actual light output of an LED?

I am building a dimmer circuit with a few discrete steps, to operate a COB LED from a constant-current source. I want the steps to appear fairly even to the eye, and am using the "square law" dimming curve relating brightness to dimmer position.

I do not have an accurate way to measure my LED's actual brightness, but can measure current and voltage using my power supply. I initially assumed that current would be the right parameter to use to estimate light output (for the purpose of dividing into equal brightness steps according to the dimming curve), but now I'm wondering if using power would give a more technically accurate result. I see lots of discussion and clarification on using current rather than voltage, but I'm hoping someone familiar with the physics of how LEDs operate can clarify whether power correlates more strongly with lumens than current alone?

At any rate, the results are very similar since the voltage does not vary strongly, and so this is more of an academic question than anything else, but I am curious.

JAE
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    I think your question may be satisfactorily answered by this other question/answer: https://electronics.stackexchange.com/q/256336/2028 – JYelton Aug 03 '23 at 01:39
  • Probably current since the emission of a photon requires recombination of an individual electron. Conversely voltage depends on a lot of things, some of which are not related to light emission (e.g. contact resistance), so unless those factors happen to cancel out, power is probably less linear than current. I'd type this as an answer, but it is speculation since I've never actually measured it. – user1850479 Aug 03 '23 at 02:25
  • Apparent brightness increases about logarithmically with lumen output. Look at LED data sheets. They show radiant output against current. [I suggest that] It's liable to be a closer fit to eye response than power as Vf rises relatively little for large increases in current. If you have few steps then a discrete step change control may be a good choice. I can make this a more considered answer "sometime" if it doesn't get any others. – Russell McMahon Aug 03 '23 at 07:15
  • Thanks @user1850479 that is helpful. My LED array drops 10V at 12mA, and 12V at 350mA, so while current is changing much more strongly than voltage, I wasn't sure where to attribute the energy associated with that extra 2V of voltage drop if not the emitted photons (but I'm way over my head on the physics). It makes sense that there are other factors like contact resistance etc. that play a role and turn the extra energy into heat, not light. If I can get access to an accurate light meter I'd like to measure this. – JAE Aug 03 '23 at 23:19
  • Thanks @RussellMcMahon, it's a good point that the datasheets use current and not power, although some of the datasheets I've been looking at ([example](https://www.bridgelux.com/sites/default/files/resource_media/Bridgelux%20DS310%20SMD%202835%201W%209V%20Thrive%20Data%20Sheet%2020191006%20Rev%20A_0.pdf)) don't include a curve at all! – JAE Aug 03 '23 at 23:22
  • Fig 13 of your cited datasheet shows relative luminous flux versus drive current. (It's easy to miss such.) – Russell McMahon Aug 03 '23 at 23:27
  • Interest only: Terrible efficiency (lumen/Watt). Marvellous CRI. Note that the flux is "pulsed flux" - ie they do not account for die heating. Real world flux will be lower. || Note too that the efficiency is always cited in lumens per Watt, not per current. THat doesn't mean that variation IS with power rather than current - just what matters most in some applications. (And lumens/amp is meaningless unless it's for a single LED and not a string. – Russell McMahon Aug 03 '23 at 23:29
  • Right you are - I skipped right over it! – JAE Aug 04 '23 at 01:13

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