How to light a home office, in three layers

Almost every guide to lighting a desk hands you one number and stops. Five hundred lux, usually. Sometimes 300, sometimes 750, always stated as if it settled the matter. It does not settle much, because a single figure describes a single light, and a desk that is comfortable to work at is lit by three of them doing three different jobs.

This page is the practical version: where each light goes, how bright it wants to be, and which sourced figure to aim it at. We are deliberately staying at the “how do I set this up” level. If you want the argument underneath the numbers — the roughly 2.6× disagreement between OSHA and CCOHS about how many lux a computer desk actually needs — that is its own page: lighting for eye strain. Here we take the sources as they are and build a desk.

Two honesty notes before any number appears. We have not metered a room; every figure below is read off a published safety standard or a manufacturer document and cited. And where a figure comes to us in foot-candles — OSHA publishes those, not lux — the lux equivalent is our arithmetic at 1 foot-candle = 10.764 lux, and we label it as ours every time.

Why one lamp cannot do it

The whole reason a desk needs layers rather than a lamp is that a screen is not paper. Paper is passive: it only shows up when you put light on it, and more light makes it easier to read until glare sets in. A monitor is the opposite — it makes its own light, needs none of yours, and actively gets worse when light lands on it, because that light bounces back as reflected glare.

So a desk holds two completely different reading surfaces with opposite lighting needs, plus the wall behind the screen, which has a third need entirely. One lamp aimed at all three will over-light one and glare off another. Three layers, each solving one problem:

• Ambient— the even, general light that fills the room so nothing reads as a dark cave next to a bright screen.
• Task— a directed light on the physical things you look at: paper, a notebook, your hands, a keyboard you cannot yet touch-type on.
• Screen (bias) — a soft light behind the monitor that lifts the dark wall closer to the brightness of the panel, without putting any light on the panel itself.

Get those three roughly right and the confident single lux number stops mattering, because you have addressed the thing it was only ever a proxy for.

Layer one: ambient light for the room

Start with the room, because it is the layer everything else sits inside. CCOHS’s lighting survey puts a general office at 500–1000 lux, and it adds the detail almost every other source drops: that level is “measured 76 cm (30 inches) above the floor”— roughly desk height, not up at the ceiling and not down on the floor. A light figure without a measuring plane is close to meaningless, and this is the plane.

The job of the ambient layer is evenness, not intensity. You want the room lit steadily enough that when your eyes flick from the screen to the wall to the doorway, the brightness does not lurch. That is what stops a bright monitor from reading as a glowing rectangle in a gloomy room — the problem this whole topic actually circles. Overhead fixtures, or a lamp bounced off the ceiling or a pale wall, spread light more evenly than a single bright point ever will.

OSHA approaches the same room from foot-candles: office lighting “should range between 20 to 50 foot-candles,” rising to “up to 73 foot-candles” where LCD monitors are in use. By our conversion that 20–50 band is roughly 215–538 lux and the 73-foot-candle figure is about 785 lux— numbers we did the multiplication for, not numbers OSHA printed. We flag them so the two systems line up, not so you chase a target to the lux. If you want to know why OSHA’s ceiling sits so far above CCOHS’s, that is the eye-strain page; for setup purposes, “an even room in the 500–1000 lux neighborhood, measured at desk height” is the whole instruction.

One nuance worth carrying into the next layer: CCOHS lists computer tasks themselves lower, at 75–300 lux, than the general room. The area right at the self-lit screen wants lesslight than the space around it — your first clue that the extra light you add for paper should be kept off the panel.

Layer two: task light for the paper

The task layer is the one people over-buy and mis-aim. Its entire purpose is to put light on the physical objects a screen’s glow cannot help you read — a document, a form, a sketchbook, the keyboard while you are still learning its layout.

Here CCOHS is unusually candid, and the candor almost never survives being quoted. Its recommended 300–500 lux for that kind of near work, it says plainly, “is not a must,” and it applies “in the situation where there is no task lamp in use.”Read those two hedges together and they describe the task lamp’s whole reason to exist: a lamp on the document is the alternativeto flooding the entire room up to 300–500 lux. Light the small area you are actually reading, and the rest of the room does not have to work as hard.

Which sets the one rule that matters for placement: the task lamp lights the document, not the display. Aim it at the paper, from the side, so the cone falls on what you are reading and nothing spills onto the glass. A right-hander sets the lamp to the left and a left-hander to the right, so the writing hand does not throw a shadow across its own work. If your desk is all screen and no paper, you may not need this layer at all — which is a real conclusion, not a gap. When you do want one, the desk lamps we could actually verify are the ones that publish their numbers rather than a sticker.

Layer three: screen (bias) light behind the monitor

The third layer targets the problem the other two only manage around, and OSHA names it in one sentence: “High contrast between light and dark areas of the computer screen, horizontal work surface, and surrounding areas can cause eye fatigue and headaches.” The subject of that sentence is contrast— the gap between the bright panel and whatever is dark next to it — not brightness in the absolute.

Bias lighting closes that gap from the wall side. It is a light placed behind the monitor, facing the wall, so the wall glows up toward the brightness of the screen and the jump your eyes make at the edge of the panel shrinks. Crucially, it puts no light on the front of the screen, so it lifts the dark surround without adding a single reflection to the glass. That is the whole mechanism, and it is a narrow, geometric one. If it sounds like your gap, the bias-lighting field is ranked on whether a strip’s white is actually neutral, which is the spec that decides whether it looks right behind a screen.

Do not confuse this layer with a monitor light bar, because they are different tools sold as the same thing. A bias light faces backward and lights the wall; a light bar clamps to the top bezel and faces down and forward to light the deskin front of the screen — closer to a task light than a bias light. Most desks want one of the two, not both, and which one depends on whether your problem is a dark desk surface or a dark wall. We work that decision through on desk lamp vs monitor light bar, and the light-bar roundup covers the clamp-and-aim option if that is your gap.

Placement: where the lights actually go

Half of good desk lighting is not brightness at all — it is angle, and it is free. CCOHS’s positioning guidance comes down to keeping bright sources out of the line between your eyes and the screen:

• Run the monitor parallel to overhead lights, not directly under them. A fixture straight above the screen reflects off the glass; the same fixture off to the side does not.
• Set the screen at a right angle to windows, not facing or backing them. A window behind you throws its reflection onto the panel; a window in front of you makes your eyes fight a bright rectangle behind a dimmer one. Off to the side, it is just daylight.
• Point every task light at the work, never at the screen or your eyes. The same rule as the task layer, restated because it is the one people break.

Rotating a desk ninety degrees costs nothing and removes more glare than most purchases, which is why it comes before any of them. The cheapest move of all lives on the monitor itself: if contrast is the mechanism, the panel is half the equation and it has a brightness slider. Turning a too-bright screen down closes the same gap a bias light closes, from the other side, for free.

The color side: lumens, Kelvin and CRI

Once the layers are placed, the bulbs raise three numbers that get muddled constantly. The U.S. Department of Energy’s LED Basics separates them cleanly:

• Lumens are light output— how much light a source puts out. This is the brightness figure; watts only tell you the energy drawn, and efficacy (lumens per watt) tells you how efficiently the two trade.
• CCT, correlated color temperature in Kelvin, is the appearanceof the light — lower numbers look warmer and yellower, higher numbers cooler and bluer. It is independent of lumens: a warm bulb and a cool bulb can be equally bright.
• CRI, the color rendering index, is how faithfully a source shows the colors of what it lights, compared with a reference.

Two of those get treated as one. Brightness (lumens) and color (Kelvin) are separate dials; picking a “cool” bulb does not make the room brighter, it makes the light bluer. The Kelvin choice for a workspace is its own question — and, like the lux one, the lighting companies do not agree on the answer — so we gave it a page of its own: color temperature for a home office.

On CRI, one caution, because it is on the box of everything now. A high CRI number looks reassuring, but the CIE — the international body behind the metric — has publicly cautioned that CRI on its own is an incomplete measure of color quality, and that it should not be relied on as the only figure, particularly for LED sources. So treat a CRI rating as one data point rather than a verdict: a high number is not a guarantee that a light looks good, only that it clears one specific test.

What this page is not

This is a setup guide, not medical advice, and it is written by someone with no standing to give the latter. Stephen reads standards documents and spec sheets; he is not an optometrist, an ergonomist or a clinician, and nothing here diagnoses anything or promises that a lamp will relieve, prevent or cure a symptom. What the three layers do is arrange light the way the sources describe — even ambient, directed task, contrast-closing bias — and keep bright reflections out of your eyeline.

If your eyes hurt consistently, that is a conversation for someone with a license and an eye chart, and no lighting layout substitutes for it. One free habit the sources do endorse and that costs nothing to try: CCOHS’s 20-20-20 rule — “At least every 20 minutes, take a 20-second break and look at something 6 meters (20 feet) away” — which is about resting your focus, not your lighting, and applies no matter how the room is lit.