Why LEDs Stay Cool but Still Heat Up
The chip's heat is conducted backwards, not radiated forward.
Cool beam, warm chip
An LED sends almost no infrared in its beam, so the light feels cool. The electrical energy not turned into light still becomes heat inside the chip, and it must be conducted away through the back of the package.
Junction temperature
The temperature at the chip, called junction temperature, controls life and brightness. Datasheets give a maximum, often around 85 to 125 degrees C, and light output falls as the junction warms.
Managing heat
- Indicator LEDs at 10 to 20 mA need no special cooling.
- Power LEDs are mounted on a metal-core board or a heat sink.
- Leave air gaps around lamps and avoid sealed, unventilated fittings.
- Reduce current if the part becomes too hot to touch.
Quick check
If a lamp base is uncomfortably hot, its heat path is probably inadequate and its life will be shorter.
Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.