If this was a joke or puzzle, the answer is one that is not turned on.
All sources of light also produce some heat. LED are our most efficient light producing the least heat today.
Here is a table with some data. The cost data is not longer accurate as LED bulbs have dropped significantly in price. The red bar labeled wasted energy is heat.
Traditional light bulbs that used tungsten filament used to produce a lot of heat. But that has changed with the advancement in technology. Light emitting diodes or popularly known as LED lights give off very less heat and generate the same amount of light with less energy consumption.
So it might be safe to say that LED Bulbs don’t produce heat. In an ideal world where energy is converted into light without any energy wasted as heat, that future bulb will be the kind of bulb that doesn’t produce any heat.
The light bulb with the lowest electrical wattage rating produces the least amount of heat.
As for efficiency, the factor to be concerned with is lumens per watt.
Of the three major electrical lighting technologies (incandescent, fluorescent, and LED), LED by far produces the most lumens per watt.
That means, for a desired illumination level, LED has the lowest wattage and, therefore, produces the least heat.
QUIZ TIME! Which produces more heat? A 100W LED bulb or a 100W incandescent?
ANSWER: Trick question. They both produce 100 watts of heat. (Notice that I didn’t say “100W equivalent LED.”)
Here’s where the trick is: the 100W LED lamp puts out more visible light than the 100W incandescent. That means is directly produces less infrared energy (heat). However, when the visible light strikes and is absorbed by other objects, it is converted to heat. So in that respect, both bulbs effectively generate the same amount of heat.
But, if you want 650 lumens of light, you can use either a 60W incandescent, a 9W fluorescent, or about a 7 or 8W LED bulb. And the lower the wattage, the less heat it produces.
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