[thinhnghiem (OP)]

Dear all
I have used a bulb which is filled in with water, it works like a convex lens to concentrate solar energy.
The performance of the water bulb gets highest level when I incline the bulb like in the clip. Solar light beam focus on a bigger dot, in compared with the dot when let the bulb standing vertically.

See my clip at

[Colin2B]

Do you have a science question?
If not we will move this to science experiments