how do LED’s work and why are they so much more energy efficient than light bulbs?
(Chemistry)
In: Technology
Normal lightbulbs work by running electricity through a small wire (filament) and heating it up until it glows. Well when you heat something to be white hot its going to give off some energy as visible light but most of it (96-98%) is going to be given off as heat (IR radiation). Normal incandescent and halogen bulbs only turn 2-3% of their energy into light.
LEDs work by exploiting some quirkier physics. If you take an electron that’s hanging out in a material with a high energy level and then you shove it across a boundary into a material at a much lower energy level then it has to get rid of the energy difference, and to do that it gives off a photon with that energy level. If you tune the difference between the energy levels you can make red, green, blue, even IR and UV LEDs, but each LED is only a single color. The LED bulbs in your home have a layer of phosphor over the LED and this phosphor absorbs the violet-UV light that the LED is setup to emit and turns it into a much broader spectrum of white light which is what you want.
LEDs have some losses because they need a power supply with some inefficiencies to provide the right voltages and currents for them to work, but a screw in LED bulb can turn 15% of the electricity it receives into light you can see while bigger commercial and industrial fixtures can be upwards of 20-28%. The upper limit for white mixing with a phosphor is about 44% so upper 20s is pretty close to ideal.
LEDs work just from the electrons in their components moving. They fit right in with the circuit and are efficient because they light up just from the electricity moving through them. Incandescent light bulbs light up because the electricity passes through them, through the filament of wire, which gets so hot it lights up. The efficiency problem is most of the energy is transferred into heat instead of light, and LEDs don’t get hot
Incandescent bulbs, as has been said elsewhere, work by getting a filament of tungsten wire hot enough to glow. This glow is across the entire spectrum, from infrared through visible light, and into ultra-violet. A lot of the energy pumped in gets released as energy which is invisible to us.
LEDs, on the other hand, release energy only in a very narrow and very specific frequency range. A red LED only emits red light. A green LED only emits green light, and so on. All of the energy gets released in the visible spectrum. Since there is no energy wasted on non-visible frequencies, we get more brightness for the same amount of energy.
The so called “white” LEDS are actually ultra-violet LEDs with a phosphorescent chemical that glows white when exposed to UV, or are a well chosen combination of red, green, and blue LEDs. Either way, their efficiency comes from the same source: not wasting power on useless parts of the EM spectrum.
As to how they work, an LED consists of P-Type and N-Type semiconductor material joined together at a junction. Electrons move through P-type material in a low energy state. Electrons move through N-Type material in a high energy state. When the electrons cross the junction, they move from a high energy state to a low energy state. When they do that, they give off a photon of light. Because the difference in the energy states is constant, the frequency of light is constant.
Traditional bulbs literally heat up a wire until it gets white-hot. They are incredibly energy inefficient.
LEDs operate on a very low-level of physics – they basically generate photons directly. Highly energy efficient (no waste heat, really), very low-power, and there to do one thing.
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