How many lumens before the fish swim away?

[tursiops]

It is not just during the day; you can see the difference between a standard and wide-angle light even at night. I have TWO 1000 lumen lights - one a Buechat that I use for night diving and the other an Epoch wide-angle for close video-clips. On a couple of occasions I forgot to recharge the Buechat's batteries on time and took the Epoch instead and the difference was obvious. The Epoch lit up a greater area close-up but lacked the penetrative ability of the Buechat.

Light obeys the Law of Inverse Squares and that explains why the illumination falls off so dramatically with increasing distance in wider-angle lights.

I think the physics is actually that even with the same about of light produced, if you spread it over a wide area, there is less light per square cm. It is not an inverse square effect, it is just a beam-spreading effect. Kind of like pouring a bucket of water into a small pan versus a really large pan....the depth of the water in the small pan will be more than in the large pan, but the total amount of water is the same.

 

[victorzamora]

I think the physics is actually that even with the same about of light produced, if you spread it over a wide area, there is less light per square cm. It is not an inverse square effect, it is just a beam-spreading effect. Kind of like pouring a bucket of water into a small pan versus a really large pan....the depth of the water in the small pan will be more than in the large pan, but the total amount of water is the same.

What you described was kind of the law of inverse squares. All inverse squares is saying is that twice the beam angle gets you 1/4 the light per "square" meaning it's less bright.

Make the pans a circle. A pan 2ft across will be 1/4 as deep as the pan 1ft across. Twice the angle, 1/4 the light.