Light Bulb Power: LED vs. Incandescent

Photo: Rhett Allain. An incandescent bulb and an LED with the same electrical power

There’s a good reason why stores don’t sell incandescent bulbs anymore — they are terribly inefficient. If you replace those bulbs with LED (light emitting diodes), you will get the same brightness for much less electrical power. There’s a pretty good demo that shows the difference between LED and incandescent, but there’s some physics to go over first.

Incandescent Bulbs

Photo: Rhett Allain. An incandescent bulb at low power

There’s nothing simpler than an incandescent light bulb. It’s just a wire (the filament) — a wire that gets hot when electric current runs through it. The glass part just keeps the air away from the filament so that it gets hot but doesn’t burn.

Of course, this leads to the big problem. The bulb wastes a bunch of energy just getting hot. Unless you are using an old Easy Bake Oven, you don’t want a hot bulb — you want a bright bulb.

Electrical Power for an Incandescent Bulb

Before getting to the LED, let’s look at the power a single incandescent bulb uses. Imagine that I have a power supply connected to the bulb. In this case, I can measure both the electric current going through the bulb (I) and the…