How many lumens do you need for a desk?

“How many lumens do I need for my desk?” is a reasonable question with an awkward answer: lumens is close to the wrong unit to ask it in. The number on the bulb box tells you how much light the bulb throws off in total. It does not tell you how much of that light reaches your desk, which is the only figure that affects how well you can see. Those are two different measurements, and confusing them is why people buy a bright bulb and still end up with a dim desk.

So this page does two things. First, it untangles lumens from lux from foot-candles, because once you see the difference the whole question gets clearer. Second, it quotes what the safety bodies actually recommend — in their units, not ours — and shows why the monitor on your desk changes the target. The deeper argument about which body to believe, where OSHA and CCOHS disagree by a wide margin, we hand off to lighting for eye strain, so we do not run it twice.

Lumens, lux, foot-candles: three different things

These get used interchangeably and they are not interchangeable.

Lumensmeasure the total light a source emits, in all directions. It is a property of the bulb or fixture, full stop — a bulb rated at 800 lumens emits 800 lumens whether it is on the ceiling, on a desk arm, or in a drawer. It says nothing about where that light goes.

Lux measures light arriving on a surface— one lux is one lumen spread over one square metre. This is the useful number, because it describes the light actually on your desk. And it depends on everything the lumen figure ignores: how far the bulb is from the surface, how wide the beam spreads, how much is absorbed by dark walls or bounced back by pale ones. The same 800-lumen bulb can give you a bright pool up close or a dim wash from across the room.

Foot-candlesare the same idea as lux in imperial units — one lumen spread over one square foot. Because a square metre is about 10.764 square feet, one foot-candle equals roughly 10.764 lux. That conversion is ours, stated so you can check it; it is a definitional relationship, not a figure either body published in the other unit. It matters because OSHA writes in foot-candles and CCOHS writes in lux, so to compare them at all you have to convert — and we would rather do the arithmetic in the open than quietly present one body’s number in the other’s unit.

The takeaway from all three: shop and measure in lux or foot-candles, treat lumens as a rough hint about a bulb’s potential, and trust a lamp most when it publishes a lux figure at a stated distance, because that is the only kind of lumen-derived number with the geometry attached.

What OSHA and CCOHS actually specify

Here is what the two bodies most often cited put on the record. Note that neither answers in lumens.

OSHA, in its Computer Workstations guidance, writes in foot-candles: “Generally, for paper tasks and offices with CRT displays, office lighting should range between 20 to 50 foot-candles.” And then, crucially for a modern desk: “If LCD monitors are in use, higher levels of light are usually needed for the same viewing tasks (up to 73 foot-candles).”By our own conversion at 10.764 lux per foot-candle, that 20–50 fc range is roughly 215–540 lux, and the 73 fc figure is about 785 lux. Those lux numbers are our arithmetic on OSHA’s foot-candle figures, not values OSHA published in lux.

CCOHS, meanwhile, writes in lux, and lands lower for the screen work. Its recommended-illumination table puts the performance of computer tasks at 75–300 lux— a range that surprises most people by how low it is — and notes that adequate general lighting is usually 500–1000 lux measured 76 cm above the floor. Separately, on eye discomfort, it hedges its office figure explicitly: “Keep in mind that recommended level of light in offices 300 - 500 lux is not a must. It applies in the situation where there is no task lamp in use.”

Put those side by side and the gap is real: OSHA’s up-to-73-foot-candle figure for LCD offices converts, by our arithmetic, to something near 785 lux, while CCOHS puts the computer task itself as low as 75 lux. That is not a rounding difference. It is a genuine disagreement about how much light a screen workstation wants, and pretending there is one tidy answer would misrepresent both. We take the disagreement apart properly, with the sources, on lighting for eye strain.

Why the monitor changes the target

The reason a desk with a screen is not the same lighting problem as a desk with a book is that the monitor is itself a light source. A book reflects whatever light you throw at it; a screen makes its own. So the job is not to flood the desk until the paper is bright — it is to keep the area around the screen in sensible balance with the screen.

OSHA names the failure mode directly: “High contrast between light and dark areas of the computer screen, horizontal work surface, and surrounding areas can cause eye fatigue and headaches.”Read it carefully, because it points in two directions at once. If the room around a bright panel is too dark, that is high contrast, and the fix is more light around the screen. But if you overcorrect and pour light onto the desk until it spills onto the glass, you have made glare, and the image washes out. The target is a balance, not a maximum. This is exactly why the raw “how many lumens” framing misleads: more output is not automatically better once a self-lit screen is in the picture.

It is also why the same room can want a different number by day and by night. Beside a window at noon, the ambient level is already high and the screen is balanced; at 9pm with one lamp on, the panel is a bright rectangle in a dark room and the contrast opens up. The level is not a single figure you set once.

Layer it: ambient first, task second

The practical shape of a good answer is not one number but two layers, and CCOHS effectively assumes this — recall that its 300–500 lux office figure applies specifically where there is no task lamp in use. Add a task lamp and the room itself can sit lower.

Ambient is the general light in the room, from the ceiling or a window, that keeps the whole space and the area around the screen from going dark. Taskis the focused light on the specific thing you are working on close up — a document, your hands, the keyboard. A moderate ambient level plus a task lamp is more comfortable, and easier to get right, than a single fierce overhead fixture trying to do both jobs. The full scheme, and the order to build it in, is on how to light a home office.

And brightness is only half of a lamp’s spec. The other half is the color of the light, measured in Kelvin, which is set independently of how much light there is — a warm 2700K and a neutral 4000K bulb can put out identical lux and feel completely different. That is its own decision, covered in color temperature for a home office.

So what do you actually do?

Stop shopping by lumens alone and start thinking in layers on the surface. Aim for an ambient level that keeps the room and the space around the screen from going dark — somewhere in the broad band the authorities describe, with the honest caveat that they disagree on exactly where. Add a task lamp for close work, placed so it lights the work and not the panel. Then adjust by looking: if the desk in front of a bright screen is clearly dim in the evening, add light there; if anything is reflected in the glass, you have too much in the wrong place. That feedback loop beats any single target number, because it is measured against your own eyes in your own room.

What we can and cannot tell you

We can tell you which unit to use: lux and foot-candles describe the light on your desk, lumens describe the bulb, and every authority answers in the former. We can quote what OSHA and CCOHS put on the record, show our conversion arithmetic openly, and point out where they disagree rather than paper over it. We can tell you the monitor changes the problem because it makes its own light.

What we cannot tell you is a single correct number, because there is not one to give — and we cannot tell you what will make your eyes feel better, because we are not qualified to and have tested nothing. OSHA’s contrast statement is a published mechanism, not a diagnosis from us. If your eyes hurt consistently, the person to see has a license and an eye chart, and no lux figure on this page is a substitute for that.