Kelvin, lumens, lux and watts measure different things. Kelvin describes the colour of the light; lumens measure the amount of light produced by a source; lux measures the light reaching a surface; and watts measure the electrical power consumed by the bulb.
Understanding the difference helps avoid one of the most common lighting mistakes: choosing only by wattage and later finding that the light is too bright, too dim or has the wrong colour for the room.
Quick summary
| Measurement | What it measures | What it helps with |
|---|---|---|
| Kelvin (K) | Colour temperature | Choosing warm, neutral or cool light |
| Lumens (lm) | Total visible light output | Knowing how much light the bulb produces |
| Lux (lx) | Light reaching a surface | Checking whether a table or work area is adequately lit |
| Watts (W) | Electrical power consumption | Understanding consumption and respecting the lamp's maximum wattage |
What are Kelvin?
Kelvin describes the colour appearance of light. A lower value looks warmer and more orange; as Kelvin increases, light becomes more neutral white and later cooler or bluer.
- 2000K: very amber and decorative.
- 2700K: warm and welcoming.
- 3000K: warm but cleaner.
- 4000K: neutral white.
- 5000K or more: cool white.
Read more in our guide to 2000K, 2700K and 3000K light.
What are lumens?
Lumens indicate the total amount of visible light emitted by a bulb. More lumens generally means a greater ability to illuminate, although the final result also depends on the shade, direction, height and colours in the room.
A low-wattage bulb can produce many lumens if it is efficient. With LED technology, wattage alone is no longer a good way to choose brightness.
Simple example
Two bulbs can both consume 8 W and produce different amounts of light. Likewise, a 5 W LED can provide more light than an older technology using more power. The useful figure for comparing light output is lumens.
What are lux?
One lux equals one lumen distributed over one square metre. Put simply, lux tells you how much light actually reaches a surface.
The same lamp can produce more lux on a book when it is close and directed towards it, and much less when it is farther away or the shade sends light in another direction.
Lux is especially useful for desks, worktops, reading tables and work areas. When buying a bulb, however, the specification you usually see is lumens.
What are watts?
Watts measure electrical power consumption. They do not directly describe how much light is produced. With LED lamps, check watts for two reasons:
- To know how much power the bulb consumes.
- To avoid exceeding the maximum wattage allowed by the lamp.
Many Valma Home table lamps use E27 sockets and specify a maximum LED wattage. Always check the individual product page before changing the bulb.
How to use all four measurements when choosing a bulb
- Check the socket, for example E27.
- Check the maximum wattage allowed by the lamp.
- Choose lumens according to the amount of light required.
- Choose Kelvin according to the atmosphere and use.
- Consider CRI if accurate colour rendering matters.
- Check dimming compatibility if the lamp or switch can control brightness.
Practical examples
Bedside lamp
2700K is often comfortable. The required lumens depend on whether the lamp is only for ambience or also for reading. A diffusing shade can soften the light and reduce glare.
Reading corner
Distance to the book matters as much as lumen output. A well-directed lamp can provide useful illumination with less total light than a lamp positioned farther away.
Living room
It is usually better not to depend on a single very high-lumen source. Distributing light between ceiling, table lamps and ambient points often works better. Read more in how to create warm, welcoming living-room lighting.
Common mistakes
- Confusing watts with brightness.
- Choosing a bulb only by Kelvin.
- Buying too many lumens without considering glare.
- Ignoring the shape and opacity of the shade.
- Exceeding the manufacturer's maximum wattage.
- Assuming every 2700K bulb looks exactly the same.
Frequently asked questions
Do more watts mean more light?
Not necessarily. Watts indicate power consumption; lumens indicate light output.
How many lumens equal one lux?
One lux is one lumen distributed over one square metre. In practice, the result depends on the area and how the light is distributed.
Do Kelvin affect lumens?
They are different measurements. Two bulbs with different colour temperatures can provide the same lumen output.
Which figure should I check first?
First make sure the bulb is compatible with the lamp. Then choose lumens and Kelvin according to the intended use. Our guide to choosing an E27 bulb brings the steps together.
To apply these concepts when choosing a luminaire, compare the specifications of our table lamps.