That’s a good point… perhaps if someone does this test, it should be compared at the same lumen level instead of the same current?
(seems like the current would probably not be a very interesting test anyway, since any two devices at the same current will tend to have similar runtimes regardless of what they actually do with the power)
I wonder what the efficiency difference might be at 1.4A, or 1.5A, or 1.9A.
The 1.9A light I just put together with a Nichia 219B is really nice, and the PWM is fast enough it looks almost the same as full current control… but the runtime won’t be as long. I never really use it above 800mA or so (average), so I could reduce its overall power to increase efficiency, but it’s nice having a turbo mode once in a while. The higher power is also nice for strobes, because a 0.3ms pulse looks brighter at 1.9A than it would at 1.4A.
For a bike tail light, I went with 700mA because djozz’s measurements show that as more efficient than 350mA or 1050mA on a red XP-E2. I don’t need it that bright, but it should increase the overall runtime at the same brightness levels, even when using PWM.
The efficiency difference is because a 50% (or whatever) constant current requires a much lower Vf, compared to a PWM'ed 50% which is full current for half the time and none for half the time (assuming both drivers do the same current at 100%). The average current might be the same for both drivers but the voltage isn't and the total power used comes from both volts & amps.
Just fyi... I wasn't sure how turbo mode works. He is saying basically it's DD - very high amps, more than the 140% increase he listed. Basically turbo takes it out of current controlled/limiting mode -- this is a very nice feature!
Also, HKJ found an issue in high mode using higher powered cells that needs a cap to be replaced, and once done, fixes the issues that HKJ was seeing. So, I'm holding off more testing til I get the cap and can mod the driver. It's a tiny 0402 -- I never worked with a cap that small, so may have a "super tech" at work do the replacement. He would have no problem doing this, so less risk than me doing it .
This HD2010, btw, is a total PIA for this experimenting because of the poor clearance for the bigger wires, big flat reflector bottom... Also the plastic LED alignment piece they ship with HD2010's now is too small for the opening, making it almost impossible to center the LED... Ugh. The older HD2010's I have didn't have this promleb- the LED alignment pieces fit much better.