I tried an amber LED with my SB800 and could not get the flash to fire, but I am not sure of the output of the amber LED I used. Of course, red worked fine, but the IR LED seemed to work the best. To test the IR LED efficiency with your flash unit, without having to purchase and IR LED, you can use a TV or cable remote control.
Obviously, as you stated, the IR would attenuate much faster though water, which is why the Nikon CLS system doesn't work well underwater. I would think with fiber optics that we would not be shooting through water. I want my light sources and receivers to be as close to each other as possible.
Thanks for the reply,
Well, a TV remote has perhaps only 3V supply (2 AAA's are kind of typical these days) but definitely has room for all sorts of voltage regulation to supply a charge multiplier to a higher voltage, caps for storage to deliver high current for the miliseconds that the IR is flickering, etc. Not necessarily a good test of what I can deliver on my own.
And now that I think about it...the Inon z240 (and z2000) photodetectors in the latest versions are designed for 'wireless' photodetector response, with
water in the path, and assuming the camera's main flash (which will be generally fairly white) as the trigger source. Put it all together and that strongly implies that the photodetector is optimized for shorter (bluer) wavelengths vs. longer, since they might assume the longer wavelengths have been attenuated before they get to the photodetector. So the yellow and amber ones I just ordered from Mouser.com might be going the wrong direction...I might be getting the best coupling if I did try a nice bright green LED after all.
Strange that the SB800's work best for you with IR or redder...maybe they were only ever designed for fiber use?
Another comment re: your current and voltage drop info above: the net 'wattage' from each might be about the same, assuming the current draw is available. With the CR2016's specifically, they're struggling to output 100mA. So given the current draw limitations of the batteries, its easier to get the light out of the visible LEDs.
All the above (plus worries about fitting the circuit into the housing - on my Sony for example I had to put the circuit board slightly offcenter atop the hotshoe, as the hotshoe location isn't centered beneath the viewfinder hump allowance on the Ike housing) sort of explains why no one has offered a simple product like this yet. Different LED colors for different strobes, LEDs either on the circuit board (like mine, to look thru the clear wall) or pigtailed to extend up to the fiber bulkhead adaptors (as in escape's images), available circuit volume, even different hotshoe mounts (I guess Sony is the only unique one, everyone else is pretty standard)...there'd have to be a lot of configurations to assure it would work. Couple that with a low count customer pool tobegin with and you end up with something that stays DIY.