If you have noticed your flashlight being warm after using it for a while, then you might be wondering whether flashlights give off heat.
Why Flashlights Become Hot
Older flashlights that are not made with CREE LED bulbs are more likely to heat up. While it’s not necessarily enough to start a fire, some old flashlights can give small burns if you are not careful.
The material that is being used also matters. Light waves emit radiation and from radiation you get heat. Some materials absorb more of the radiation heat while some others are not as absorbent.
Here is a great answer from this thread: https://www.candlepowerforums.com/vb/showthread.php?220978-Does-light-give-off-heat
“There are two forces at work here: 1. Yes, there is infrared radiation being given off by the light source, moreso with incans than LEDs. Some of that infrared will get transmitted out of the front of the flashlight, just like the visible light is. One of the reasons LEDs are more efficient than incans is because they produce less infrared per input watt than incans do. 2. When em radiation strikes a surface, three things happen. Some is reflected, some is absorbed, and some passes through. If the surface is a mirror, most is reflected, some is absorbed, and essentially none passes through. [The reason mirrors used in very high power lasers are silvered on the front is to cut down on the absorbsion. If the silvering was on the back side the substrate (glass, plastic, etc.) would explode from the amount of energy it would absorb over a very short period of time] A surface like a piece of paper will obviously reflect less energy away, and will absorb more. Sometimes even enough to reach ignition temperature.”