I use an old S2 w/2.1A driver as my EDC and frequently tailstand it on my dresser in the morning while getting dressed so as not to disturb my wife. I had the original “2-group” driver with the annoying low mode blink & memory. I used to have an old XM-L T6 4C in it, but changed it over to an XM-L2 T5 5B1. The 5B1 is without doubt my favorite tint and the one that most realistically represents colors to me.
I finally got my self setup and educated to flash my own firmware and flashed STAR (regular on-time memory). I set it up with no memory and modes of: 3.5% - 34–100. I found low was still too bright and “on-time memory” (even on a driver with “no memory” since it affects mode changing while the light is on) was really driving me crazy! So I added the off-time capacitor and reflashed STAR Off-time with low adjusted down to 1.4% (I aimed for 1% and actually got 1.4). The off-time memory work fantastic (exactly as expected) and now I know what all the rave was about! Low could still be adjusted a little lower though. I am one that does not light “moonlight” (i.e. a barely glowing emitter that doesn’t hurt your eyes to stare into) as I see no real purpose for it (not for me anyway). My guess would be that something around 0.5 output in my case would be ideal. It’s really nice being able to tweak firmware and reflash drivers to give you exactly what you want!
About your decision on which driver (2.8A vs 2.1A, etc. . . ). I agree with others that you can always choose a lower mode and only use max as needed. With custom firmware you could create a “Turbo” with or without a timer (I’m out of the loop on temperature sensor firmware) and have high up around 75% or so where turbo is barely a step up for “max” while “high” is your normal able to run unlimited time high mode. My S2 at 2.1A will get hot on high after a minute or two, but it’s not scalding. I’ve never tried to keep it on high for long periods of time though. (I have discovered it in my pocked switched on by accident and feeling hot.) I know user Comfychair has posted up that he would let similar lights (like S6, S3) run on high (2.8A? not sure) sit and run for long periods to prove that no damage was done and that the bodies could handle the heat. I feel the 2.1A version is a good level for the S2 and good balance of runtime with output (2.1A draw on a Panasonic NCR18650B 3400mAh cell tested at 3,128mAh @ 2A draw would yield approximately 1.49hr runtime (3128/2100=1.49) and I calculated 470 lumens out-the-front in my D.I.Y. sphere on my previous XM-L T6 4C emitter). I will be retesting my S2 again in the near future. I also need to get back to my sphere work and analyze how my sphere calibration is working out.
Also - I posted this “”color rendering comparison”:User Review: Nitefighter BT40S ( CAt Review ) | Page 9 | Mountain Bike Reviews Forum over at MTBR awhile back which might be helpful. (I spend most of my time over there nowadays.)
-Garry