How Do
LED Lights Work?
An LED is a semiconductor chip that emits light when current passes through it. The bulb you buy adds a driver to convert mains electricity to the right voltage plus a phosphor coating to make blue chip emission look white. That is the entire technology in three sentences.
LED stands for Light Emitting Diode. An LED chip is a small semiconductor that emits light directly when electrical current passes through it (a process called electroluminescence). Modern white LED bulbs use a blue chip with a phosphor coating that converts some of the blue light to yellow plus red wavelengths, producing the appearance of white light. The bulb base contains a driver circuit that converts UK mains AC voltage (230V) to the low-voltage DC the chip needs (typically 3 to 12V). LEDs are 80 to 90 percent efficient at converting electricity to light versus 10 percent for incandescent bulbs. That is why LEDs use far less power for the same brightness.
The figures that matter
First LED
First red LED demonstrated in 1962. Took until the 1990s for white LEDs to become viable.
Efficiency
LED converts roughly 85 percent of input electricity to light. Incandescents convert 10 percent.
White LED
Modern white LEDs use a blue chip plus yellow phosphor coating to produce white light.
LED voltage
Low-voltage DC the chip needs. The driver converts mains AC to this.
Four things to consider
Direct light from semiconductor
Electroluminescence. Current flows across a junction, releases energy as photons. No filament, no gas, no heat.
Driver does the heavy lifting
Converts UK mains 230V AC to 3 to 12V DC. Determines bulb quality, dimming behaviour plus lifespan.
Phosphor makes it white
Pure blue chip plus yellow phosphor coating creates the appearance of white light. Different phosphor mixes create different colour temperatures.
8 to 10x more efficient
LED produces 100 to 150 lumens per watt. Incandescent produces 10 to 17 lumens per watt. Halogen produces 15 to 25.
The technology inside an LED bulb explained
An LED bulb is essentially three things glued together: a semiconductor LED chip, a driver circuit plus a heatsink-housing assembly. Each plays a specific role.
Component 1: The LED chip. A small piece of semiconductor (usually gallium nitride for blue LEDs. Or aluminium gallium indium phosphide for red, yellow, green) about the size of a pinhead. When current flows across the chip's p-n junction (the boundary between two doped semiconductor regions), electrons combine with holes plus release energy as photons. The wavelength of those photons determines the colour. Blue LEDs emit around 450 to 470 nanometres. Red LEDs around 620 to 640 nanometres. The chip itself is what does the actual lighting.
Component 2: The phosphor coating. Pure blue chip light alone would be a harsh blue colour. Modern white LEDs use a yellow phosphor coating over the blue chip. Some of the blue light hits the phosphor plus is converted to yellow. The combination of blue passing through plus yellow emission appears white to the human eye. Different phosphor blends produce different colour temperatures: heavier phosphor for warm white (2700K), lighter for cool white (5000K).
Component 3: The driver. The driver is the circuit board in the bulb base. It does three things. First, it converts UK mains AC (230V at 50Hz) to the low-voltage DC the chip needs (typically 3 to 12V depending on bulb type). Second, it controls current to keep the chip operating at its design point (LEDs are current-driven, not voltage-driven, so steady current matters more than steady voltage). Third, it handles dimming if the bulb is dimmable, by changing the duty cycle of pulsed power to the chip.
Component 4: The heatsink. Even though LEDs are far more efficient than older bulbs, they still produce some heat (15 to 20 percent of input electricity becomes heat rather than light). The heatsink (usually aluminium fins or a heat-conductive plastic shell) pulls heat away from the chip plus driver, dissipating it into the surrounding air. Better heatsink design equals longer chip plus driver life.
Why LEDs are so much more efficient than older bulbs. Incandescent bulbs heated a tungsten filament until it glowed. Most of the input electricity (around 90 percent) became heat. Only about 10 percent became visible light. Halogens were similar. LEDs use direct electroluminescence which produces light from electrical energy with very little waste. The efficiency gap is roughly 8 to 10 times in lumens per watt.
What this means in practice. A 10W LED produces around 800 lumens. A 60W incandescent produces around 800 lumens. Same brightness, one-sixth the electricity. Across the bulb's 25,000 to 50,000 hour lifespan, the running cost saving is hundreds of pounds per bulb. Plus the LED lasts 15 to 25 times longer than the equivalent halogen.
Lumens, watts plus the lighting label. UK LED packaging uses two key numbers. Lumens measure brightness output (the amount of light produced). Watts measure electricity consumption. Old habits associated 60W with a certain brightness. With LEDs you should buy by lumens instead. 800 lumens is the most common single-bulb output. 1,500 lumens is bright. 400 lumens is dim. Watts on an LED package only matter for running cost calculations.
Real number ranges
Why LED costs less to run than older bulbs
What happens when you switch on an LED bulb
Driver activates
Mains AC 230V flows into the driver. Driver converts AC to low-voltage DC (3 to 12V) for the LED chip.
Chip emits light
Current flows across the p-n junction in the chip. Electrons release energy as photons. Light appears instantly.
Blue becomes white
Some blue chip light hits the yellow phosphor coating plus is converted to yellow plus red. Combined output appears white.
Driver maintains current
Driver holds the chip at its design current. Chip produces steady light. Heatsink dissipates the small amount of waste heat.
Four things that determine LED bulb quality
Driver quality
Premium drivers run cooler, dim smoothly plus last longer. Cheap drivers fail first plus cause flicker.
Chip quality plus binning
Better chips produce more lumens per watt plus more consistent colour. Premium brands use higher-binned chips.
Heatsink design
Larger plus better-ventilated heatsinks pull heat from the chip more effectively. Extends lifespan plus efficiency.
Phosphor quality
Better phosphor blends produce more accurate colour rendering (CRI 90+) plus more pleasant warm tones.
Compare the options
LED bulb
- ✓Semiconductor electroluminescence. Light from current across a chip junction.
- ✓100 to 150 lumens per watt efficiency.
- ✓15,000 to 50,000 hour lifespan.
- ✓50 to 80°C surface temperature. Cool to touch.
- ✓Driver electronics required. Determines quality.
Incandescent bulb
- ✗Filament heated to incandescence. Light from heat-glow.
- ✗10 to 17 lumens per watt efficiency.
- ✗750 to 1,000 hour lifespan.
- ✗250°C+ surface temperature. Causes burns.
- ✗No driver needed. Filament directly takes mains AC.
Understanding how LEDs work helps you make better choices on bulbs, fittings plus dimmers. Our full LED Lights hub covers safety, troubleshooting, installation plus selection across LED bulbs plus strip lighting.
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This article is one chapter inside our complete LED Lights knowledge base. The hub covers safety, troubleshooting, installation plus selection across LED bulbs, strips plus tape lights for UK homes.
More on LED lights
Three further LED foundation articles in the same hub group cover related questions. The first is what does led stand for in led lights for the basic terminology. The second covers what are the led lights for the broader category introduction. The third is how long do led lights last for the related lifespan question.