Office lighting: what lumens, lux and UGR really mean

Watts are the last thing that matters in office lighting. Here is what actually decides whether a room is good to work in — in plain language, based on the European workplace lighting standard EN 12464-1:2021.

The six words you need

Lumens (lm) — how much light leaves the fixture, like litres from a tap. Lux (lx) — how much lands on the desk: 1 lx = 1 lm per m². An office desk needs 500 lx; a cosy living room sits at 100–150 lx; a cloudy day outside is 1,000–5,000 lx.

Maintained illuminance — the standard asks how much light you will have after 3–5 years, when LEDs have aged. Design with a maintenance factor of 0.80: to keep 500 lx, install about 625 lx.

Uniformity (U₀) — darkest point divided by average; 0.60 for desks. Even light tires the eye less than bright-and-dark patches.

UGR — the glare rating. For offices with screens look for UGR ≤ 19: a room with 600 lx and UGR 25 is a worse workplace than 450 lx with UGR 16. Cheap opal panels give light but glare; microprismatic diffusers solve it.

CRI (Ra) — how faithful colours look, 0–100. Ra ≥ 80 is the minimum, Ra ≥ 90 makes skin and materials look real. Many products in our catalogue now show this value in their specifications.

What the standard requires

Since 2021 the standard also looks at walls (≥ 150 lx), ceilings (≥ 100 lx) and light on faces (150–300 lx) — essential for video calls.

Placement rules

• Never place fixtures behind the person — reflections hit the screen and the eyes.
• Linear fixtures run parallel to the windows.
• Desks with their long side parallel to the window; working plane at 0.75 m.
• Wall distance = half the fixture spacing, or the walls stay dark.

Quick estimate

Fixtures = (lux × area) ÷ (lumens per fixture × 0.55 × 0.80). A 40 m² office with 3,600 lm panels needs ≈ 13 fixtures. Aim for 5–8 W/m². Start with our lighting calculator.

We offer free consultations and site visits in the Varna region — see our services.