Room Lux Calculator
Tell it the room size and what the space is for, and it works out how many fixtures you need, how many lumens that is, and what it costs you in watts. Free, no sign up.
Your room
You need about
11
fixtures of Downlight 12W
That lands you at roughly 206 lux, against a 200 lux target.
Floor area
26 m²
Suggested layout
4 × 3
Spacing
5 ft × 4.7 ft
Total load
132 W
What this means
Your room is 26 square metres and needs about 13,200 lumens in total to reach 200 lux. Spread over 11 fixtures that is 1,200 lumens each, drawing 132 watts altogether, or 5.1 watts per square metre.
An estimate, not a lighting design. It assumes an even ceiling grid, mid range wall and ceiling colours, and a working plane 0.8m off the floor. Dark walls, odd shapes, high racking or a narrow beam angle will all pull the real figure around.
Lumens, watts and lux, in plain terms
Lumens
how much light comes out
The total light a fitting produces. This is the number to compare when you are shopping. It is printed on the box, usually next to the wattage.
Watts
how much electricity goes in
What it costs to run, not how bright it is. LED broke the old habit of judging brightness by wattage. A 9W LED can match an old 60W bulb.
Lux
how much light lands on the surface
Lumens spread over an area. One lumen falling on one square metre is one lux. It is what you actually experience in the room, and it drops as the room gets bigger or the ceiling gets higher.
The one that trips people up
Two fittings both marked 18W can differ by a third in actual output, because one runs at 70 lumens per watt and the other at 110. If you buy by watts you are guessing. Ask for the lumens, then divide by the watts to see how efficient it really is. Anything near 100 lumens per watt is respectable for LED today.
How the numbers are worked out
This uses the lumen method, the same approach used for a proper lighting layout.
fixtures = (target lux × floor area) ÷ (lumens per fixture × UF × MF)
UF, the utilisation factor. Not all the light reaches the floor. Some is absorbed by the walls and ceiling. Tall narrow rooms lose more than wide low ones, so the calculator works this out from your room shape and ceiling height rather than asking you for it.
MF, the maintenance factor. Dust settles on fittings and LED output fades slowly over the years. Designing to exactly the target means being under it within a year or two, so we allow for it up front. 0.8 is the normal assumption indoors, lower in a dusty workshop.
Recommended lux levels here follow the usual ranges in Malaysian Standard MS 1525 and the international EN 12464-1. They are guidance rather than law for a home, but for offices and workplaces they are what an inspector or a consultant will expect.
Common questions
How many lumens do I need per square metre?▼
Multiply your target lux by the floor area, then add back what the room loses. A 20 square metre living room at 200 lux needs 4,000 lumens landing on the floor, but you have to supply more than that because light is absorbed by walls and lost over time. In practice that room usually needs somewhere around 8,000 to 10,000 lumens of fittings. The calculator does that step for you.
What is the difference between lumens and watts?▼
Lumens measure the light coming out. Watts measure the electricity going in. In the incandescent days the two moved together, so people learned to shop by watts, and a 60W bulb meant a known brightness. LED broke that link. A 9W LED can produce the same light as an old 60W bulb. When you compare fittings, compare lumens. Watts only tell you what it costs to run.
What is a good lumens per watt figure for LED?▼
Around 100 lumens per watt is normal for a decent LED fitting today. Cheap ones sit at 70 or lower, and good ones reach 130 and above. Two fittings both marked 18W can differ by a third in actual light output, which is why buying by watts alone leaves you guessing.
How many lux should a room have in Malaysia?▼
As a rough guide, a living room sits around 150 to 200 lux, bedrooms about 100 to 150, kitchens 300 with 500 over the worktop, a study or home office 300 to 500, retail floors 500, general factory work 300, and warehouse storage around 150. Malaysian Standard MS 1525 and the international EN 12464-1 both set out recommended levels by task if you need something more precise.
Why does the calculator ask for ceiling height?▼
Because height changes how much of the light actually reaches the floor. A high ceiling spreads light over a wider area and loses more of it to the walls before it gets down to you, so the same fitting delivers less lux at the working plane. It also affects spacing, since fittings mounted high need to be further apart to avoid overlapping into hot spots.
Is this good enough to buy from?▼
It is good enough to plan with and to sanity check a quotation. It assumes an even ceiling grid, mid range wall colours and a clear room. Dark walls, tall racking, odd room shapes and narrow beam angles all shift the answer. For anything you are committing money to, send us the room and we will go through it with you.
Want a second opinion on the numbers?
Send us the room and what it is for. We will tell you honestly if the calculator is close, and what we would actually put in.
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