Bulb used as convex lens

[thinhnghiem]

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

https://www.youtube.com/watch?v=f0Nvc6Q_Ulw

[Q-reeus]

So you have progressed from toy magnet rockers as perpetuum mobiles, aired with slight variations over four different threads in another forum site, to the thoroughly understood case of a spherical convex lens. Anything new in that YouTube demo worth discussing?