LED Glossary for Beginners
Short definitions of common LED terms you will meet again and again.
The Ultimate LED Glossary for Beginners
Brightness and efficiency
Lumens (lm)
Lumens measure the total amount of visible light emitted by a source. In the past, people looked at wattage to guess brightness. With LEDs, you look at lumens. More lumens mean a brighter light, regardless of how much power the bulb uses.
Wattage (W)
Wattage measures how much electrical energy a bulb consumes. Because LEDs are highly efficient, they use very few watts to produce a high amount of light. For example, a 10W LED can often replace an old 60W incandescent bulb.
Efficacy (lm/W)
Efficacy represents the efficiency of a light bulb. It is calculated by dividing the total lumens by the wattage used (lumens per watt). A higher efficacy rating means the bulb gives you more light while using less electricity.
Colour quality
Color Temperature (CCT)
Correlated Color Temperature describes the appearance of the light emitted by a bulb. It indicates whether the light looks warm (yellowish) or cool (blueish). Color temperature is measured on the Kelvin (K) scale:
- Warm White (2700K – 3000K): Cozy, relaxing light ideal for bedrooms and living rooms.
- Neutral/Natural White (3500K – 4100K): Crisp, balanced light perfect for kitchens and workspaces.
- Daylight (5000K – 6500K): Bright, intense light with a blue undertone, great for reading, garages, and security.
Color Rendering Index (CRI)
CRI measures how accurately a light source reveals the true colors of objects compared to natural sunlight. It is scored on a scale from 0 to 100. A CRI of 80 or higher is good for everyday home use, while a CRI of 90 or above is excellent for art studios, retail displays, and makeup vanity areas.
Power, heat and lifespan
LED Driver
An LED driver is a self-contained power supply that regulates the electricity flowing to an LED. Think of it like a translator; it converts standard household alternating current (AC) high-voltage electricity into the low-voltage direct current (DC) that LEDs require to function safely without overheating.
Heat Sink
A heat sink is a component built into an LED fixture that absorbs and dissipates excess heat. While LEDs do not emit heat in their light beam like old bulbs do, their internal components still generate heat. The heat sink keeps the bulb cool, which is crucial for preserving the LED’s long lifespan.
Rated Life
Rated life is the expected lifespan of an LED bulb, usually measured in hours. Instead of suddenly burning out like traditional bulbs, LEDs slowly dim over time. The rated life usually marks the point where the bulb emits 70% of its original brightness (known in the industry as L70). Many home LEDs feature a rated life of 15,000 to 50000 hours.
More key terms
- Anode: positive terminal of an LED.
- Cathode: negative terminal.
- Forward voltage (Vf): voltage across a lit LED.
- Forward current (If): current through a lit LED.
- Reverse voltage: voltage applied the wrong way; limited to about 5 V on most small LEDs.
- Current-limiting resistor: resistor in series that sets LED current.
- Millicandela (mcd): unit of directional brightness for small LEDs.
- Viewing angle: beam width at half intensity.
- Forward bias: connecting an LED so current flows.
- Junction temperature: temperature of the chip itself.
- L70: hours until light output falls to 70 percent.
- PWM: switching on and off quickly to control average brightness.
- SMD: surface-mount device, soldered flat on a board.
Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.