What a light bulb and an egg have in common?
All In The Details
The shell of an egg and the glass exterior of a light bulb have more than one thing in common. First, both protect something delicate inside: the exterior of the light bulb keeps the delicate internal wiring protected and an eggshell protects a developing chick. The need to protect chicks and wiring requires that eggshells and light bulbs be structurally strong.
Second, both are made of thin material. A chick, ready to hatch, has to be able to peck its way through the shell. And because light bulbs are usually made of opaque rather than clear glass, the glass exterior must be thin so that light can shine through.
So how can a structure be strong and yet made of thin material at the same time? By using a carefully-designed oval shape.
Think About This
Picture for a moment a square egg. If you took that imaginary object in your hand and squeezed it very hard between your thumb and finger, the pressure you'd exert would be localized in the exact part of the flat surface your thumb and finger were pushing. Even a slight pressure would be great enough to break the thin shell into pieces. But if you do the same thing to a real egg, the force you exert is not localized in one point, but is distributed into all directions around the surface of the egg. Though you can eventually break an egg by doing this, it takes a great deal more force to do so.
Of course, it's no coincidence that the shapes of light bulbs and eggs are similar. When the light bulb was invented and perfected, it was patterned after a shape that nature had come up with hundreds of thousands of years ago.