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
Double-convex lens. Give us the approx. angles at noon and at sundown, then tell us why they are different.
