Lighting a space correctly is not only about the Watt value of a bulb or floodlight; what matters is the amount of light that must reach the working surface (lux). Use the tool below to estimate the required lumens, total LED power (W) and number of fixtures for a home, office, garden, car park, workshop, factory or CNC/machine area, based on the area, mounting height and target lux.
How is LED lighting calculated?
The key metric for correct lighting is lux — the amount of light on the working surface (1 lux = 1 lumen per m²). Required lumens are found as: Required lumens = Area (m²) × Target lux ÷ Utilization factor ÷ Maintenance factor. The utilization factor depends on mounting height (it drops as height rises) and the maintenance factor on environment dirt. The tool applies both automatically; total LED power is Watts = installed lumens ÷ LED efficacy (lm/W).
Approximate target lighting levels by area:
| Area / task | Approx. target |
|---|---|
| Corridor / transition | 50–100 lux |
| Living room / general home | 150 lux |
| Kitchen, bathroom, work surface | 300 lux |
| Office / desk | 500 lux |
| Workshop general | 300 lux |
| Machine / CNC work area | 500–750 lux |
| Precision control / fine assembly | 750–1000 lux |
| Garden path / outdoor | 30–50 lux |
| Car park / security | 75–150 lux |
Color temperature (Kelvin): 2700–3000K warm (living room/bedroom), 4000K neutral white (office/kitchen/most work areas), 5000–6500K cool white (workshop/inside machines). At the same lumens, color temperature does not change the lux need, only perception. CRI: CRI 80+ for general indoors; choose CRI 90+ for detailed work such as paint, cable color and part inspection. Especially inside CNC and machines, several light sources from different directions reduce shadows. Critical areas should be verified with a lux meter after installation.
Lumen, lux, watt and candela: the difference between the four
Most lighting mistakes come from confusing these four units.
| Unit | What it measures | What it means in practice |
|---|---|---|
| Lumen (lm) | Total light produced by the source | The “output” of the fixture |
| Lux (lx) | Light falling on a surface (lm/m²) | How much light actually reaches the machine table |
| Watt (W) | Electrical power consumed | The bill — only indirectly related to light |
| Candela (cd) | Light intensity in a given direction | Beam focus in spots and floodlights |
Watts are no longer a measure of light. The same 50 W can produce 4,000 lm or 6,500 lm — the difference is efficacy (lm/W). A good industrial fixture today sits in the 120–150 lm/W range; anything below 80 lm/W is either an older generation or has an optimistic label.
⚠️ Stroboscopic effect: the invisible hazard of LED in a workshop
This is the most critical and most overlooked lighting topic in machine shops. LED fixtures with poor drivers fluctuate in brightness 100 times per second on a 50 Hz supply (120 on 60 Hz). The eye does not notice it.
But a rotating chuck, turret, drill or milling cutter turning at a speed that coincides with that frequency appears to be stationary or turning very slowly. No further explanation is needed for why an operator might reach toward a chuck they believe has stopped. This is not a theoretical risk; it is a known accident mechanism in industry.
Protection comes from driver quality. The European Union’s Ecodesign regulation (2019/2020) introduced two limits for mains-operated light sources placed on the market from 1 September 2021:
- PstLM ≤ 1.0 — visible flicker limit
- SVM ≤ 0.4 — stroboscopic visibility measure
When selecting fixtures for areas with rotating parts, ask for both values in the technical documentation. If they are not stated, do not use that product there. There is also a practical field test: point a phone camera at the fixture — if you see banding or flicker on the screen, the driver is weak. It is not a precise measurement, but it eliminates bad products quickly.
As an additional measure, use DC-supplied or high-frequency driver fixtures for machine-mounted task lighting, and distribute general lighting across different phases so that the ripple on one phase is filled in by the others.
Worked example: a 200 m² machine shop
Scenario: 200 m², ceiling height 6 m, target 500 lux (a typical value for machining under EN 12464-1), medium dirt level.
- Raw light requirement: 200 × 500 = 100,000 lm
- Utilization factor (6 m height, medium reflectance): ~0.60 → 100,000 ÷ 0.60 = 166,667 lm
- Maintenance factor (medium dirt): 0.80 → 166,667 ÷ 0.80 = 208,333 lm installed
- At 130 lm/W efficacy: 208,333 ÷ 130 ≈ 1,603 W total
- With 150 W high-bay fixtures: 1,603 ÷ 150 ≈ 11 units
Power per square metre: 1,603 ÷ 200 ≈ 8 W/m². That is reasonable for a 500 lux target; if your calculation exceeds 15 W/m², either the efficacy is low or the factors were chosen too pessimistically.
Why several fixtures instead of one big lamp?
The calculation gives you the total lumens but says nothing about how to distribute them. Two concepts decide that:
- Uniformity (Uo): The ratio of the minimum illuminance to the average. In work areas it should not drop below 0.60. A handful of powerful fixtures may hit the average while leaving dark patches in between.
- Glare (UGR): Target UGR ≤ 19 in offices and ≤ 22 in general industrial areas. When an intense point source enters the field of view, the operator sees the lamp instead of the part.
A practical rule: the spacing between fixtures should not exceed roughly 1–1.5 times the mounting height. At 6 m, a 6–9 m grid gives a uniform distribution. Also place task lighting to the side of the operator rather than behind them; otherwise their own shadow falls on the work area.
Choosing fixtures for a workshop environment
| Environment | Protection rating | Why |
|---|---|---|
| Office, technical room | IP20 | Enclosed and clean |
| General workshop | IP54 | Dust and splashes |
| Near machines, coolant mist | IP65 / IP66 | Oil vapour and pressure washing |
| Inside the machine (work light) | IP67 / IP69K | Direct coolant jet |
Coolant mist seeps into fixtures with an inadequate protection rating and kills the driver within months. Polycarbonate diffusers can also react chemically with certain coolant additives and craze — near machines, prefer glass or a chemically resistant material.
Colour temperature and CRI: why they matter in inspection work
At the same lumen output, colour temperature does not change the lux requirement, but it changes perception and fatigue. In a workshop 4000–5000K is usually the most balanced choice; 6500K looks crisp but is tiring over long shifts.
CRI (colour rendering index) is a separate matter. CRI 80+ is enough for general lighting; but ask for CRI 90+ for surface quality inspection, detecting scratches and burrs, reading cable colour codes, and paint or coating checks. Pay particular attention to R9 (saturated red): many cheap LEDs show a general CRI of 80 while R9 is near zero, so red tones are not rendered correctly.
Five common mistakes
- Replacing old fluorescents watt-for-watt. The logic of “36 W LED instead of a 36 W fluorescent” gives the wrong result; the comparison must be made in lumens.
- Skipping the maintenance factor. A system that just meets the target at installation falls 25% below it in two years through dust and lumen depreciation.
- Not asking about driver flicker. In areas with rotating parts this is a workplace safety issue, not a comfort issue.
- Looking only at average lux. Without checking uniformity, the machine table can be dark while the walkway is over-lit.
- Not measuring after installation. The calculation is an estimate; the real value is measured with a lux meter at working height (typically 0.85 m above the floor).
Frequently asked questions
Can a machine work light replace general lighting?
No, the two are used together. General lighting sets the base level of the area; task lighting adds the extra lux needed at the point of work. With task lighting alone, the eye constantly adapts between a bright spot and dark surroundings and tires quickly.
Why are more lumens needed as height increases?
For two reasons: light intensity falls with the square of the distance, and as the mounting rises a larger share of the light spreads onto walls and non-working areas. The utilization factor represents that loss. In high ceilings, narrow-beam (for example 60°) high-bay reflectors reduce it.
How far can I trust this calculation?
This tool applies the average calculation known as the lumen method and is adequate for pre-sizing. In complex spaces where racking, machines and partitions cast significant shadows, a point-by-point simulation in software such as DIALux or Relux should be used for a definitive result.