How bright should a bedside lamp be? Dim it and see

Bright enough to read, dim enough to sleep

A bedside lamp has two jobs that pull in opposite directions. For ten or twenty minutes it has to let you read a page without squinting. Then it has to stop getting in the way of sleep. Most lamps are bought for the first job and left on for the second.

The useful number is not how bright the bulb is, but how much light actually lands on the page. That is measured in lux (lumens per square metre). For comparison, an office is usually lit to roughly 300–500 lux, while a typical family living room in the evening is nearer 50 lux. Light also fades quickly with distance: move a lamp twice as far away and the page gets about a quarter of the light. That is the inverse-square rule, and it is why a small lamp close to the book can beat a big one across the room.

What the numbers mean in your room

Try the reading preset: around 400 lumens, 50 cm from the page, gives a page level in the low hundreds of lux, which many people find comfortable for print. Slide the bulb down to 100 lumens at the same distance and the page drops to a level that is fine for a quick look at your phone but tiring for a novel. A lamp does not need to be strong to work, it needs to be close and aimed at the page.

Now look at the second readout, the light reaching the pillow beside you. A partner trying to sleep a metre or so beyond you gets a small fraction of what your page gets, and a shade that points down keeps it smaller still. If you share a bed, a low, shaded lamp on your own side is kinder than one tall bulb that lights the whole room.

Why the last half hour matters

Light in the hours before bed also tells your body clock that the day is not over. In a study of 104 people, ordinary room light (under 200 lux) in the eight hours before bedtime delayed the rise of the sleep hormone melatonin to about 23 minutes before bedtime. In dim light (under 3 lux) it started nearly two hours before. Melatonin also lasted about an hour and a half longer in dim light.

That does not mean you have to sit in the dark. It means the last stretch of the evening is the time to go low: a warm, dim lamp instead of the ceiling light, and the dimmest setting that still lets you read. The warmer colour helps too, because the bluer part of the light is the part that affects the body clock most. Slide the colour slider and notice how a lower number looks closer to candlelight.

Setting it up without buying anything

• Move the lamp before you replace it. Bringing it 20 cm closer to the page does more than doubling the bulb.
• Swap only the bulb. A dimmable warm-white bulb in the 2200–2700 K range costs little and fits the lamp you already own, provided the cap matches (check the old bulb, and the packaging says if it is dimmable).
• Use a lower bulb in the lamp, not a second light. One low source is calmer than several.
• Aim it. Turn the shade so the opening faces the book, not your partner or your eyes.

Measure before you buy

If you decide a new lamp is worth it, measure first. Check the height from your mattress top to the bedside surface and the width of the table, so the lamp's base fits with a glass of water and a book. Lay a tape from where your head rests to the table edge to find the distance your lamp would be from the page, and check the cord reaches the socket without crossing a walkway. Anything that plugs into the wall should be used as the maker describes, and a lamp that gets warm should not sit under bedding or curtains.

A second-hand lamp from a friend or a market is a perfectly good start. A new shade and a new bulb often change a tired lamp more than a new lamp would.