LEDs

Aah! The lamp went out! I’ll change the bulb. Ouch! It's hot.

That's an old-fashioned bulb with a metal filament. That's why it's hot. Here’s a new one. This is the wrong kind! It says 10 W on this one, and the old one says 60 W.

Yes, that's right, but it will give as much light as the old one. The new one wastes less energy on heat. Let’s look at how the new bulb works. Inside the bulb are several diodes that light up — light emitting diodes. We shorten ‘light emitting diodes’ to LED.

Let’s zoom in on one of them. Here is a small tile. The tile consists of two different semiconductors, which together make a diode. When each is made of certain materials.. ..then something interesting happens. When the lamp is switched on, current flows.

And when electrons in the current jump from one semiconductor to the other, energy is released by atoms emitting light particles: the diode emits photons. And this makes the lamp light up. The old bulb lights up when the current passes through the filament. Then it glows and emits light - and heat. But a LED does not get hot because it does not need anything that glows.

The current that passes through the filament bulb is converted mostly into heat; only a small part becomes light. But the current flowing through the diode is converted almost entirely into light. A 10-watt LED bulb provides about as much light as a 60-watt regular light bulb. Although a LED does not get very hot like a regular light bulb, there is another thing that gets hot. When LED lights are connected to the wall socket, this thing is needed — a transformer.

A transformer gets the right voltage and converts alternating current to direct current. It gets hot — but not as hot as a bulb with a filament, and so it doesn’t waste as much energy. The LED bulb is more energy efficient. LED lights are everywhere, not just in Leon’s ceiling light. This little red dot on the TV is a small LED.

When we look at the whole thing, it looks like this. A small LED with two legs. One leg is longer than the other, and there is a point to it. LEDs only conduct current in one direction, and to make it shine you have to connect it correctly. The shorter leg, the cathode leg, must be connected to a negative pole and the longer one, the anode leg, to a positive pole.

LEDs come in a range of colours depending on what kind of semiconductors they are made from. Different semiconductors emit light with different amounts of energy, with different frequencies, when current passes through them. More energy produces blue light and less energy red light. Look! Now we have several different colors!

Fun! Now you can have a… disco?