Pick the room, enter its floor area and the lumens printed on your fitting’s box. The calculator uses Suruhanjaya Tenaga’s recommended lux table and shows every step, so you can see how many lights the room needs and why.
Recommended average illuminance from Suruhanjaya Tenaga’s energy-audit guideline, which references MS 1525 — treat the home figures as a guide, not a rule.
Length × width of the room, in square metres.
Zumtobel’s reference: 0.67 for a clean room, 0.50 for a very dirty one. Change it if your maker gives another figure.
Leave blank if the datasheet gives none — the result is then shown before room losses.
The two relationships. Zumtobel’s lighting handbook defines illuminance as E (lux) = luminous flux (lumens) ÷ area (m²). Lighting output drops as fittings age and gather dust, so designers apply a maintenance factor. Zumtobel's lighting handbook suggests 0.67 for a clean room and 0.50 for a very dirty one when no specific data is available — i.e. plan for about a third more light than the bare lumens-per-area sum.
The arithmetic. So the calculator works out lumens needed = target lux × area ÷ maintenance factor, and divides by the utilisation factor too if you enter one from the datasheet. Fittings needed = lumens needed ÷ lumens per fitting, rounded up. That combined line is arithmetic on the two relationships above, not a formula quoted from a standard, and it assumes the light is spread evenly.
The targets. Suruhanjaya Tenaga's building energy-audit guideline lists recommended average illuminance of about 100 lux for bedrooms, 150 lux for a lounge, 150-300 lux for kitchens, 150 lux for bathrooms, 100 lux for toilets, 100 lux for corridors, passageways and stairs, 200 lux for restaurants, 300-400 lux for general offices, shops and reading or writing, and 200-750 lux for shops, supermarkets and department stores. The table sits in ST's energy-audit guideline, which references MS 1525 (a code of practice for non-residential buildings), so treat the home figures as a guide rather than a rule for houses.
Brightness is not everything. Lighting makers group colour temperature into warm white (up to about 3,300 K), neutral white (3,300-5,300 K) and cool white (above 5,300 K). For colour rendering, Ra above 80 counts as good and above 90 as very good, and below 80 should not be used at workplaces (Zumtobel lighting handbook). To place the fittings evenly, use the downlight spacing calculator.
| Factor | How it changes the result |
|---|---|
| Target lux | The biggest lever: a kitchen at 300 lux needs twice the lumens of one at 150 lux. |
| Floor area | Lumens needed rise in step with the area. |
| Lumens per fitting | Read it from the box, not the watts — more lumens per fitting means fewer fittings. |
| Maintenance factor | 0.67 plans for about a third more light than the bare sum, to allow for ageing and dust. |
| Utilisation factor | Room shape, wall colours and optics lose light; a datasheet figure below 1 raises the count. |
Rules of thumb from named lighting makers and ST’s recommended lux table — not a Malaysian design standard. The fitting’s beam angle and datasheet change the answer.
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