- Oct 3, 2008
For some time ago I had GU10 based Cree replacement bulb named "Solarox". In about 15 minutes it got very warm and in 30 minutes it was uncomfortably hot to touch. At this point I used to cool down the bulb by just grabbing the heatsink for a while and the temperature decreased significally in just under minute. I confirmed the temperature drop with other hand so that possible skin temperature raise didn't matter.
Flashlight manufacturers also know this and that's why they usually warn about leaving light on max power unattended(= out of your hands).
For cooling via your hand to take place the surface temperature must be above your skin temperature. (If not, the light is cooling your hand, not the other way around). If this effect is to be any effective, the light should be quite warm to hold. If it doesn't feel warm to hold, your hand is not cooling it. As your experiment confirms, the hand is able to cool a WARM bulb/flashlight.
Another aspect when holding the light is that the light will be MOVING. There are few circumstances where you will hold the light absolutely still when in your hand. Even though your level of activity may be low, the increase in airflow versus a light lying still on a table is substantial.