What Are CRI, Kelvins, and Lumens: A Lighting Terms Guide
Why These Terms Matter
When buying an LED fixture or bulb, you'll find many numbers and abbreviations on the packaging: lumens, kelvins, CRI, watts... Understanding what they mean helps you choose lighting that truly fits your needs.
Lumens (lm) – Light Output
Lumens indicate how much light a lamp emits. More lumens = brighter light. Watts only show energy consumption, not brightness!
Kelvins (K) – Color Temperature
Color temperature, measured in kelvins, describes the light's hue — from warm yellowish to cool bluish. 2700 K is warm white (like old incandescent bulbs), 4000 K is neutral white, and 5000–6500 K is cool daylight.
CRI (Ra) – Color Rendering Index
CRI shows how accurately light renders colors compared to natural light. The scale goes from 0 to 100, where 100 means perfect color rendering. For home use, choose CRI ≥ 80; for kitchens and bathrooms, CRI ≥ 90.
Quick reference by room
| Room | Lumens | Kelvins | CRI |
|---|---|---|---|
| Living room | 200–300 lm/m² | 2700 K | ≥ 90 |
| Bedroom | 100–200 lm/m² | 2700 K | ≥ 80 |
| Kitchen worktop | 500–750 lx | 4000 K | ≥ 90 |
| Bathroom mirror | 300–500 lm/m² | 3000–4000 K | ≥ 90 |
| Home office | 400–500 lm/m² | 4000–5000 K | ≥ 90 |
Watts are not a measure of light
Choosing bulbs by wattage is a habit left over from incandescents, where power and light output tracked each other. With LED they do not: the same 800 lm can come from a 9 W or a 12 W bulb — only the efficiency differs. Judge efficiency in lumens per watt; good LED bulbs now reach 80–110 lm/W.
| Incandescent | LED equivalent | Light output |
|---|---|---|
| 40 W | 5–6 W | ~470 lm |
| 60 W | 8–9 W | ~800 lm |
| 75 W | 11–12 W | ~1050 lm |
| 100 W | 14–16 W | ~1520 lm |
What the packaging does not tell you
Flicker is barely perceptible in a good bulb and tiring in a cheap one — film it with your phone and look for bands on screen. Beam angle decides whether the light lands where you need it: 30–40° for spots, 120° for general lighting. Warranty shows how much the manufacturer trusts the product. More on flicker in why LED bulbs flicker.
Frequently asked questions
How many lumens does a room need?
Multiply the floor area by the recommended density: a 20 m² living room at 250 lm/m² needs about 5000 lm spread across several sources.
What is the difference between lux and lumens?
Lumens are the total light a bulb emits; lux is how much of it reaches a surface (1 lx = 1 lm/m²). Work areas are specified in lux, bulbs are labelled in lumens.
Is higher CRI always better?
Better for colour, but CRI ≥ 95 bulbs cost more and are often slightly less efficient. CRI 90 is plenty at home; 80 is fine for a garage.
Summary
The three numbers answer three different questions: lumens — will it be bright enough; kelvins — does the tone suit the space; CRI — will colours look natural. Browse our LED bulb range or get in touch.
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