Why do heating elements only give off light when heating up?

Question

The heating elements in my toaster oven only give off light when they are heating up. Once the toaster is fully heated, the heating elements go dark. I assume the elements give off light due to the change in temperature occurring during the heating process? And once there is no more change in temperature, they stop?

Answer 1

The elements become much hotter than the cooking temperature set when the oven is heating up -- this is to bring the oven to the desired temperature quickly. During this "heat up" period, the elements are hot enough to produce visible light. When the oven's temperature finally matches the cooking temperature, the elements can cool off and become the desired cooking temperature as well. Most likely this desired cooking temperature is less than is required for the elements to produce light.



Hope this helps!

Answer 2

At about 600 ˚ C red light is emitted. As the temperaure rises more colours like blue is emitted along with the red light, When the temperautre is raised to 1000 ˚ C almost all colors are emitted and the mixture will look white.



There is no chance for the filament to look black.

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Light from incandescent bulbs and fires: A lightbulb has a glowing wire with a somewhat lower temperature, resulting in yellow light, and something that is "red hot" is again a little less hot. A wood fire at 1500 K puts out peak radiation at 2000 nm . This is far more energy in the infrared than in the visible band, which ends about 7500 Å.

Answer 3

Anytime their temperature is hot enough to emit visible light...it does...as per the phenomena of black body radiation.

http://en.wikipedia.org/wiki/Black_body



ALL THE TIME that they are above the temperature for being red-hot...they are emitting red light.



The onset temperature of being red hot is typically about 800 Kelvin. Colder than that, and all emission is infrared. Hotter than that, and you can see the tail-end of radiation emissions.





When operated in steady state, you should indeed see them continuously glowing red. In steady state, by definition, THERE IS NO CHANGE IN TEMPERATURE.



Adding of heat doesn't always mean increase in temperature. The electrical energy adds heat at a constant rate. If there is LESS heat leaving than is added, the element rises in temperature. If there is more heat leaving than added, then the element cools off in temperature.