Which option is better?

EFMax

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Imagine two lights, one has a 12* spot and puts out about 2000L, the other has a 28* flood but puts out 3000L.. Both lights use the same bulb but different reflectors and lamp housing.

Assuming off road use and a need for good side vision as well as distance coverage, how would one workout (based on your own previous experiences) which light would give the appearance of best lighting ratio.. (also assume that you can't try before you buy).. cheers..

I know its a compromise but in my head I can't quite see if the side vision from the flood is offset by its ability to penetrate as deeply as the spot or does its extra output take its distance ability close to or beyond the spot. Manufactuers have no beamshot comparisons and the difference in price is not OTT.. TIA.
 

FrontRanger

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Imagine two lights, one has a 12* spot and puts out about 2000L, the other has a 28* flood but puts out 3000L.. Both lights use the same bulb but different reflectors and lamp housing.

Assuming off road use and a need for good side vision as well as distance coverage, how would one workout (based on your own previous experiences) which light would give the appearance of best lighting ratio.. (also assume that you can't try before you buy).. cheers..

Even among different lamp/optic combinations that have the same (advertised) beam width, there's quite some variation. The beam width is usually based on the angle at which the intensity (luminous flux per area) is 1/2 of the maximum value. But the overall beam pattern determines things like the amount of spill and the sharpness of the spot-to-spill transition. The lack of trying it is the problem. Notice when reading the bicycle headlamp threads that the builders often say they're pleased with their new light, except they want to try new optics. Absent proper documentation from the manufacturer, experimentation is key.

I know its a compromise but in my head I can't quite see if the side vision from the flood is offset by its ability to penetrate as deeply as the spot or does its extra output take its distance ability close to or beyond the spot. Manufactuers have no beamshot comparisons and the difference in price is not OTT.. TIA.

Assuming that the two beam widths are quoted at the same intensity, the average intensity falls off as the inverse square of the beam width. So the 3000 lm light's main beam intensity will, on average, be scaled by (28/12)^2*(3000/2000), only about 27.6% as intense as the 2000 lm light at a given distance. It will cover more area, but the 2000 lm light will out-throw the 3000 lm light by a noticeable margin (nearly a factor of 2 for distance with identical beam intensity).

It depends on how fast one rides and how twisty the trails are, but I would choose the 2000 lm with 12-degree beam. Even a small amount of spill from 2000 lm ought to be adequate. And if not, you can try to supplement it or (more CPF-ishly) mod it. Ok, you asked for an opinion and you got one! :D
 
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mechBgon

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With that much light on tap, I'd go with the floodiest beam possible, for a bar-mounted off-road light. Where I ride, the bike pitches up and down, the bars are panning left & right, and so a bar-mounted light that has a pronounced hotspot has that hotspot flying all over the place. Bright-dim-BRIGHT-dim illumination. With a flood beam, there's not so much of that effect. If you're talking helmet lights, then that might be another ball of wax.

So that's my two cents :)
 
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FrontRanger

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Opinions appreciated... thanks.

Sure. I can also appreciate what mechBgon said about the hotspot flying all over the place. I have several lights, two of which have beamwidths of about 4 and 6 degrees. They're meant for road riding, but I've tried them off road. For that use they were definitely not good, for the exact reason mechBgon describes. But I consider a 12-degree beam to be somewhere between a spot and a flood. If the transition from beam to spill is smooth, I'd still choose it. But if the transition is sharp, then you would indeed be more likely to suffer the problem that mechBgon describes. Unfortunately a simple "beam width" figure isn't enough to tell.

Come to think of it, you really ought to have beamshots. Lamps of 2000 and 3000 lm are not likely to be cheap. Along with expense ought to come proportionate amount of support from the maker. Have you asked for the beamshots? Just a thought.

P.S. mechBgon: Nice username. My commuter is also sans derailleur.
 

mechBgon

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P.S. mechBgon: Nice username. My commuter is also sans derailleur.


Hehe, the "mech" in this case refers to a BattleMech, actually ;) I live in the US so it would be "derailleurBgon" if I were referring to bike parts :grin2:
 

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