If you point two 100 lumen flashlights at a spot do you then get 200 lumens on target? Sometimes when doing wall bounce tests it seems that if i point one hot spot over the other flashlights hot spot it doesnt really seem to get much brighter. Lumens dont measure the spot though correct?
I know they have flashlights with say 3 crees that are rated 3x a normal cree though.
Is this some sort of trick to my eye?
Maybe i just dont know enough about how light is measured....
First off, for clarity I'll give the definition of relevant units:
Lumens are the total power
output (not input/battery draw) of the light, weighted by how sensitive your eyes are to the color of the light. A UV light for example would produce zero lumens no matter what since it is invisible.
Candela/Candlepower is a measure of how concentrated your light is, so it's your lumens output divided by the beam angle. Narrower beam angles mean higher candela.
Lux, or lumens/square-meter is a measure of how much light falls onto a surface. This is the easiest way to measure light output using a simple meter, so it's often referred to on the forums. Our eyes have a logarithmic response to lux -- that is why it's possible for our eyes to work in such different situations as under moonlight (less than 1/10th lux), indoor lighting (100s of lux) or direct sunlight (as much as 100,000 lux).
In the case you talked about, looking at the bright hotspot on the walls, there's another factor that comes into play. Because of the bright hotspot, your pupils will be likely to contract, limiting the amount of light they'll allow in. This is why it's not practical to use a concentrated light meant for throw to work up close. If you were to point two diffused lights at a wall instead, it would be easier to discern a difference.