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Illuminance Converter
Convert between lux and foot-candles for lighting design.
A hospital operating table needs roughly 1,000 times more light than a hallway at night. Illuminance is what actually quantifies that gap — not how bright a bulb is, but how much light is actually landing on a surface — and getting it wrong in either direction has real safety consequences.
Lux versus foot-candles
- Lux (lx) — the SI unit of illuminance, defined as one lumen of light spread over one square metre. Used almost everywhere outside the United States.
- Foot-candle (fc) — one lumen spread over one square foot. Still the standard in US lighting codes and architectural specifications.
- Conversion factor — 1 foot-candle equals 10.764 lux, because a square foot is smaller than a square metre, so the same lumen output is more concentrated.
Recommended light levels
| Setting | Lux | Foot-candles |
|---|---|---|
| Moonlit night | 1 | 0.1 |
| Hallway, corridor | 50–100 | 5–10 |
| Living room | 150–300 | 14–28 |
| Office desk work | 300–500 | 28–46 |
| Detailed reading, drafting | 500–1,000 | 46–93 |
| Surgical operating table | 10,000–100,000 | 930–9,300 |
Why offices settled on 300–500 lux
That range is not arbitrary. Below roughly 300 lux, close reading and screen work start to cause measurable eye strain over a full working day. Push much past 750–1,000 lux in a general office and you introduce glare, especially on screens, without a real benefit to task performance. The recommended range represents a genuine balance point tested across decades of workplace-lighting research, not just a convention.
Specialised tasks break that rule deliberately. Surgery demands extreme illuminance because the margin for missing detail is measured in millimetres, while a bedroom or cinema deliberately targets a tiny fraction of office lighting because the task there is comfort, not visual precision.
Illuminance conversion questions
How do I convert lux to foot-candles?
Divide the lux figure by 10.764. A room lit to 500 lux works out to about 46.5 foot-candles. Going the other way, multiply foot-candles by 10.764 to get lux.
Why does the US use foot-candles while most other countries use lux?
Foot-candles were built into US lighting standards and building codes before the country adopted metric units for most other measurements, and architectural and engineering specifications have simply never fully switched over. Lux is the SI unit and is used in the metric-standard rest of the world.
What lux level is recommended for reading?
Around 500 lux for sustained close reading or detailed work, compared with roughly 150–300 lux for general living spaces. Task lighting, like a desk lamp, is often used specifically to boost a small area up to that higher level without over-lighting the whole room.
Does lux measure the brightness of a light bulb?
Not directly. A bulb’s total output is measured in lumens; lux measures how much of that light is actually landing on a given surface, which depends on distance, angle and the size of the area it is spread across. The same bulb produces very different lux readings up close versus far away.
Why does an operating table need so much more light than an office?
Because surgical tasks require distinguishing extremely fine detail with essentially zero margin for error, and shadows or low contrast under standard lighting could obscure something critical. Surgical lighting is engineered specifically to be shadow-free at very high illuminance, far beyond what any general workspace needs or could comfortably tolerate.
