The flashlight on the left uses an incandescent bulb, Strion LED Flashligh while the one on the right uses LEDs to give white, Bulb LED Flashlight red, blue, and infrared lightRecently, red led flashlight flashlights that use light-emitting diodes (LEDs) instead of conventional lightbulbs have become available. LEDs have existed for decades, mainly used as low-power indicator lights. In 1999, Lumileds Corporation of San Jose, California United States, introduced the Luxeon LED, a high-power white-light emitter. This made possible LED flashlights with power and running time better than some incandescent lights. The first Luxeon LED flashlight was the Arc LS, designed in 2001.

LEDs can be significantly more efficient than incandescent lamps at lower power levels, so they use less battery energy than incandescent lightbulbs. Such flashlights have longer battery lifetimes than incandescent lamps of comparable light output. LEDs are also less fragile than conventional glass lamps.

Some LED flashlights electronically regulate the voltage supplied to the LEDs to stabilize light output as the batteries discharge. By contrast, the light output of non-regulated flashlights changes proportionally to the voltage supplied by the battery, resulting in a significant decline in output as battery voltage declines. LEDs also have the advantage of maintaining a specific color temperature regardless of input voltage or current, while the color temperature of an incandescent bulb declines with the power available.

LED flashlights may consume 1 watt or more from the battery, producing heat as well as light. Heat dissipation for the LED often indicates that LED flashlights have aluminum bodies to dissipate heat and can become warm during use.