Originally Posted by
mechBgon
Beam pattern is also quite important. I was doing my highway commute route the other day with my DiNotte 600L and my Dereelight DBS, and while the DBS is "only" a ~250-lumen light, it completely dominates the 600L for actually seeing forward down the highway, because the light goes where I need it. I'd compare it to driving with one's parking lights, then switching on the low-beams. Lumens are one factor to look at, beam pattern's another.
Absolutely right! That's why I advocate describing headlight performance by the following four numbers:
1) Total Lumens
2) Hot Spot Lumens
3) Total Divergence
4) Hot Spot Divergence
All four numbers are easier to measure with my first system above, which is why I started with that one instead of the sphere. The sphere is easier to take to bike shops for comparisons, but the benchtop system gives a better picture more accurately. Perhaps with the addition to a camera looking down on the target to see beam shape as well.