Question

Why does a electric bulb glow in yellow and CFLs in white colours?

Answer 1

INCANDESCENT BULB:
An incandescent bulb (classic) works by heating the tungsten filament. When you heat something, it will begin to glow, first in infrared we feel as heat, then in colors we see in the rainbow, starting with deep red, then orange, yellow, and white. Higher temperatures produce blues and ultraviolets, but by this time most metals are melted. Even with tungsten, one of the metals with the highest melting point, the temperature where it glows white, makes the metal very fragile. It breaks easily.
So, to make bulbs last longer, they make them so they burn at a lower temperature and glow with a yellow.
C F L :
Compact Fluorescent Lamp requires a start up time to attain full brightness. The light colour is slightly greenish at power on which changes to blue white after the warm up period of a few minutes. This bluish white colour is due to the presence ofUltraviolet rays from the excited mercury vapour. The CFL has aresonant converter to generate high frequency AC to excite the mercury vapour filled inside the tube. The excitedmercury atoms generate UV rays that produces fluorescence in the Phosphorcoating of the tube. The phosphor coating then emits visible light with some UV fraction that gives bluish white colour to the light.