Light bulb Heat and Light Relationship
Country: United States
Date: March 2008
Do light bulbs that produce much heat
also produce much light?
A typical ordinary tungsten filament light bulb "throws away" about
95% of its electrical energy as heat. The remaining 5% is converted
into light. This is true for a small 40 Watt lamp or a large 150 watt
one. Halogen lights are a little better than this, being up to about
10% efficient. As you can see, any type of tungsten filament lamp has
pretty poor efficiency. You can think of them as "heating elements
that also happen to produce a little light".
Higher wattage bulbs do produce more heat, but that is because they
use more power. They also produce more light in the process. But the
ratio of light output to heat output (that is, "efficiency") remains
much the same whether the light is a small one or a large one.
There are some special tungsten lamps that are designed to produce
more heat and less light. These are generically referred to as "heat
lamps" and are often installed in bathroom ceilings to keep you warm
after you get out of the shower. They are the same as ordinary lights,
except that the filaments are designed to operate at a lower
temperature compared to normal lamps. The lower temperature results in
less light, and more infrared heat.
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Update: June 2012