Most of us never think about the light we work in until our eyes feel tired and gritty by mid-afternoon. Often it is not the screen itself but the mismatch between the screen and everything around it. Your screen should be easy to read without appearing to glow like a lamp, and when it is much brighter or darker than the room, your eyes have to keep adapting between different light levels. Glare, reflections and big differences between bright and dim areas can all add to visual discomfort, tired eyes and headaches.

The two-minute brightness check

1. Sort the room before the screen

Turn on enough general lighting to see your desk, keyboard and the area around your screen comfortably, and avoid working with a bright screen as the only light in a dark room. Where you can, position the screen so neither you nor the screen directly faces a window. Sitting at roughly a right angle to the window usually makes reflections easier to control, and softening bright sunlight with a blind or curtain works better than turning the screen up to its maximum.

2. Open a white page

A blank document, email or mainly white webpage gives you a consistent surface to judge the screen by.

3. Compare the screen with the room

Put a sheet of white paper beside the screen under your usual lighting, then look at the paper and the white part of your screen from where you normally sit.

• If the screen looks noticeably brighter or seems to glow, bring the brightness down a step or two.
• If the screen looks grey or dull and the text is hard to make out, take the brightness up a little.
• Stop when the white area looks about as bright as the paper and the text stays clear.

The two do not need to match perfectly. You are just making sure the screen is not the brightest or darkest thing in front of you. There is no single correct percentage either, since 50% looks very different on different monitors and the right setting shifts as the room changes.

4. Check for reflections

Show a dark image or turn the screen off for a moment, then look for windows, ceiling lights or lamps reflected back at you. If you can see one clearly, it usually helps to try these before touching the brightness:

• Adjust the blinds or curtains.
• Move or angle the lamp.
• Turn or slightly tilt the screen.
• Move the screen or desk if that is practical.

Turning the brightness up might make things easier to see, but it does not remove the source of the glare.

5. Adjust the text, not just the brightness

When text feels hard to read, more brightness is not always the answer. You could try:

• Increasing the text size or display scaling.
• Raising the contrast between the text and background.
• Cleaning fingerprints and dust off the screen.

For most work in a normally lit room, dark text on a light background is clear and copes better with reflections than light text on a dark background.

6. Recheck through the day

A setting that feels right in the morning can be too dim in bright afternoon sun or too bright after dark. It is worth repeating the white-page check when:

• The sun moves round the room.
• You open or close the blinds.
• The main lights go on or off.
• You move between home and the office.
• You start working in the evening.

Automatic brightness helps, but it is still worth a quick look to check the result suits your space.

What to change in different lighting

• Bright daylight. Deal with the direct sun first using blinds or curtains, then raise the brightness only enough to keep the text clear. Try not to sit with the screen right in front of a bright window.
• A normally lit room. A moderate brightness plus the white-paper check usually does it. The screen should look like part of the room rather than a separate light source.
• A dim room or evening. Bring the brightness down and switch on a soft lamp beside or behind the screen, so it lights the surroundings without shining into your eyes.
• Reading printed pages. Use an adjustable desk lamp aimed at the paper. Paper work often needs more local light than screen work, and a desk lamp gives you that without brightening the whole room.

What about night mode and warmer colours?

Light also has a colour tone. Cooler light looks slightly blue and suits daytime, while warmer light looks slightly yellow and often feels gentler on the eyes in the evening. Most phones, tablets and computers have a setting that warms the screen as the day goes on, usually called something like Night Light or Night Shift in your display settings. Many people find it more comfortable, though it works best alongside sorting out your brightness, glare and room lighting rather than instead of them.

It is also worth knowing that blue-light filtering glasses are not a reliable fix on their own. A Cochrane review of 17 randomised trials found they probably make little or no difference to computer-related eye strain.

A quick final check

Your lighting is probably about right when:

• The screen is clear without glowing.
• You are not squinting or leaning in to read.
• No windows or lights are reflected on the screen.
• You can comfortably see your keyboard and desk.
• Moving your eyes between screen, desk and room does not feel jarring.