Why is electric bulbs made spherical in shape

A light bulb can have any shape, but look at nature : an egg is a very strong construction. A light bulb is of that egg shape because we also like it to be a strong construction.
;)

If you're talking about incandescent light bulbs, then it's because the gas inside is at a low pressure, and a sphere is a stronger shape to withstand this pressure and is easier to manufacture. You also need room for the filament. However it's not necessary for bulbs to be spherical now that we have better manufacturing techniques.