Why 60 Watts incandescent Bulb Glow in Yellow color

Why 60 Watts incandescent Bulb glow in Yellow color?

Incandescent bulb works under the principle of thermal radiation. In our home application incandescent bulb works by heating of the tungsten filament. When we start the switch, the tungsten starts heating up. At first we see in the rainbow, starting with deep red, then orange, yellow, and white and blue… here higher temperature produces deep blue color and lower temperature produces red color. Here we make bulb with tungsten, one of the metals with the highest melting point, the temperature where it glows white, makes the metal very breakable. It breaks easily. So, to increase the bulb life hours, they make them not to burn at a lower temperature and glow with a yellow color. That’s why our 60 Watts incandescent bulb glows in Yellow color (mixed with white).

Notes of Why 60 Watts Power incandescent Bulb glow in Yellow color:

  • To get white light from the 60 Watts Bulb, we can increase the temperature of the tungsten filament by increasing the voltage across it, But the tungsten may get blow off.
  • At same time, you can see in your house, when the voltage across the bulb is less, the bulb glows in pure yellow color.

Image ref: https://lumicrest.com/colour-temperature/

How the manufacture makes the bulb to glow in yellow color as fixed?

The manufactures control the tungsten temperature by changing the resistance of the tungsten materials, As you know from ohms law,

Hence the change in the resistance of the filament material changes the current through it.


From Heat produced …

Output heat increase as the square of the current. that’s why the bulb manufacture makes the tungsten only to discharge yellow color radiation by adjusting the resistance.

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