What are the advantages of having a multi-LED vs. single LED flashlight ? As I see it, a multi-LED light would need to provide power to multiple emitters and therefore each emitter would necessarily be dimmer (assuming the same power source and drive current) than if a single emitter was used. You could drive a multi-emitter light harder than a single emitter, but only at the expense of run time (for a wow effect, perhaps). Or am I missing something ?
Thanks,
Mike
Actually, if you look at Cree spec sheets, or better yet, the PCT, you can see that the LED’s are more efficient at lower wattage. So, for the same exact power supply, multiple LED’s will perform better than a single emitter. The throw is likely to be much less (again, assuming the same power source and drive current as the single emitter), because your light output is coming from a larger collective die area. So, multiple LED lights are better for flood than for throw. Clear as mud now? 
There are two ways to look at multi emitter setups.
For instance if you had a single emitter driven at 3amps. You get lots of output but also lots of heat and the emitter is quite a long way over its rated specs and being inefficient.
If you had a triple setup where you fed each emitter 1amp. You run times would be the same as you are still using the same amount of energy. The difference is most acres emitters are a lot more efficient at 1amp rather than 3amps. So while each led won’t be as bright they will in total be putting out slightly higher lumens due to the increased efficiency. Chances are as they are more efficient you’ll have slightly less heat too. These gains are likely to be marginal however.
The other big difference will be beam profile. Fitting 3 emitters into the space of 1 emitter means you’ll have to use smaller optics/reflectors. So you’ll typically get a more floddy beam on multi emitter setups.
Of course depending on the driver you use. You could for example run each of the 3 emitters at 3amps. So 9amps in total. This will obviously reduce runtime and produce a tonne more heat. But also a shed load more lumens too. Good drivers will offer enough modes so you can still run it efficiently at lower levels.
Marginal? Well, it depends on how you look at it, I guess. It’s been said that to the eye, it takes almost double brightness to look significantly brighter. In that regard, the gains might be called marginal. But, also by that definition, most of the gains we strive to achieve every day are marginal. According to PCT, both XM-L2 and MT-G2, in their respective highest bins, gain about 100 lumens going from one emitter at 1.5A versus three emitters at 0.5A each. The XP-G2 gains about 150 lumens making the same change.
Not only that, but the wattage isn’t actually the same between the set-ups, as you suggested it is. The Vf goes up/down with the current draw of the emitter. So, one emitter pulling 1.5A has a higher Vf than three emitters sharing the same 1.5A among them. That means, you would actually see run-times increase a bit, although maybe marginally. 