Heat energy transmitted from Lightbulbs

[johnl]

They say that incandescent bulbs waste a lot of energy in the form of heat, while cfl's do not. I want to understand why this is so. They both produce white light? Is it a difference in the radiated spectrums of each type of bulb, or does it have to do with the mechanics of making light by glowing the element in the incandescent vs light emission from the excited gas in the cfl? I don't know the answer, trying to figure it out.

 

[mgb_phys]

Incandescent lights produce radiation across the visible band and out into the infrared,
The amount of light they generate at each wavelength depends on the temperature - typically about 2000-3000K, so in this graph you can see that only a small amount of the light in in the visible band

CF produce only a few narrow wavelengths in the visible band, by balancing the amount of red, blue and green they produce it looks white.

 

[johnl]

So, would it be correct to say that the light produced by cfl's isn't actually "white light", in that the spectrum is actually narrow?

 

[mgb_phys]

Correct - like a TV it makes white by mixing red/green/blue
The exact ratio depends on the gas mix and coatings on the bulb and so depends on the manufacturer -
you can design to either give an output like a regular bulb or a blue-er output that is closer to daylight.