Why do light bulbs have a circular shape?

Other than the ease of manufacturing as mentioned in other answer, spherical shape has other benefits too. For square or rectangular shapes, additional stress will be generated in corner points during the glass cooling when the bulb is just switched off. read more

The only reason they are circular is the ease with which circular bulbs can be made. The method of development is that there is circular frame into which molten glass is blown so that it takes the shape of the circular frame. read more

Incandescent light bulbs are gradually being replaced in manyapplications by (compact) fluorescent lamps, high-intensitydischarge lamps, light-emitting diodes (LEDs), and other devices,which give more visible light for the same amount of electricalenergy input. read more