Desk Lamp Lumens and Light Bar Size Calculator
Estimate how many lumens your desk lamp needs from your task, work area and existing light. Compare a light bar size starting point alongside colour temperature and CRI.
For a useful starting point, measure before you calculate: take a work-surface reading with the task lamp off and enter it as existing light below. Phone readings are approximate; a calibrated meter is needed for reliable absolute values.
Workspace and task
Area to illuminate
The 20% default is an illustrative assumption, not a measured lamp efficiency. Beam spread, aim and height change this share; compare several values and verify the installed lux.
Accent & Contrast Tuning
Estimated desk lamp output
450 lm
90 lm must reach 0.18 m², assuming 20% of lamp output reaches that area.
An estimate of required emitted lumens, not a product rating or a measurement of your desk.
Desk lighting spec and spread Calculated values
What to do with these numbers
- Measure at the work surface, sensor flat where your hands and documents are, not up near the fixture.
- Aim the bar forward and down. Tilted back, it paints a bright band across the top of the screen.
Read next
- Desk lighting for screen work: glare, CRI, and lux targets — where these targets come from.
- How many lumens for a desk lamp? — reading lamps, 800 lumens and the difference between lumens and lux.
- Monitor light bar buying guide — reading a spec sheet against these numbers.
- Bias lighting vs monitor light bar — which fixture fixes which complaint.
- Monitor light bar problems — flicker, fit and USB power faults.
How the lumen estimate works
The IES definition of lux is one lumen per square metre. This calculator multiplies the extra illuminance needed by the work area, then divides by your assumed fraction of useful lamp output.
Lamp lumens = max(0, target lux − existing lux) × area in m² ÷ (useful output % ÷ 100)
For example: 500 lux over 60 × 30 cm needs 90 lumens arriving on that area when existing light is zero. If 20% of the lamp's emitted output lands there, the estimate is 450 lumens; at 10%, it is 900 lumens. These are calculated examples, not measured performance. Existing room light reduces the additional output required.
The task presets are editorial starting points. OSHA's workstation guidance describes office lighting around 215–540 lux and up to about 785 lux for LCD viewing tasks. LEDiL's office-lighting overview describes a broader task-area range up to 1,000 lux. The precision preset uses that broader range.
The light bar length estimate uses the site's rough proportion of 1.5 cm per inch of display diagonal. It does not account for aspect ratio, curvature, mounting clearance or beam optics, and cannot guarantee coverage. Compare the manufacturer's illuminated area at a stated height and check the bezel fit before buying.