Originally Posted by
notnormal
Source? I've never seen those sort of figures before. First, MR16 has a larger reflector then an mr11 so the beam is better focused. All else being equal, a 20w MR16 does not produce twice the lumens of a 20W MR11. Second, halogen lamps provide around 15-20 lumens per watt. Third, overvolting by 20% yields around ~85% gain but reduces the bulb life by 90%. So that high end 5000 hour bulb will only have a 500 hour life. Fourth, look at the manufacturer's MR11/MR16 lumens/spread chart for a comparison. Fifth, enough poster on this forum, and others, have already shown that a 3xcree setup beats a 20W halogen light.
Other advantages of the P7 include, less heat, better efficiency, and no cables to snap while off-road mountain biking
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I've used overvolted mr11&16s for commuting for years, I find them more than adequate. Main problem is efficiency and resulting battery requirement.
I've never used 2x20w lamps because it's overkill for my needs, plus would have too little runtime with the batteries I own.
A mr16 is in fact much brighter than the same (20w) rated mr11. You would know this to be true in a second if you had ever actually compared them. This is the main reason why DIYers use mr16. MR11s aren't as bright, they're hard to find, and significantly more expensive.
I don't see how you could be using 2x20w mr16s, overvolted, and have the resulting illumination pale in comparison to an inexpensive p7 flashlight.
I sincerely hope I'm wrong, since I'm all for inexpensive bicycle safety enhancements. Either leds have taken huge leaps in the last year, or you have some crummy mr lights.
I don't read this forum regularly; I'm not obsessed with bike lights. If you have beamshots comparing 2x20w mr lights to a p7 emitter, then please kindly post them or direct me to them by link so that I might evaluate them myself.
BTW, MR16 bulbs cost 2 bucks at lowes - lifespan, cost - it's trivial. 500hrs=5000miles.
I've used the website below occasionally for ideas, and have based decisions and comments on the data presented there. It may be inaccurate. If you have better information, please share it.
http://nordicgroup.us/s78/
http://nordicgroup.us/s78/wattslumens.html