Short answer: a night light disturbs your sleep least when it gives off little or ideally no light below 500 nanometres, burns as dimly as possible, sits low rather than at eye level, and is on for as short a time as possible. Of those four, the studies show the amount of light matters most, and it is also the best tested: light things as dimly as you can.
The background on why is in the article on which light disturbs your sleep and which does not.
Four properties, in order of importance
1. How much light it gives
This is the one most often overlooked, because everyone focuses on colour. The circadian response to light depends on the dose: more light means more effect, even within the same colour. In the study by Schöllhorn and colleagues (Communications Biology, 2023), sleep latency and the shift in melatonin onset rose steadily as melanopic irradiance went up.
For a night light, that means: pick one you can really turn down low. Enough to see your way to the bathroom, no more. A dimmable light set to ten percent does better here than a non-dimmable one with a more favourable colour.
In the article “Is red light in the evening better than dimmed white light?” under the heading “Brightness differs per home and per room” I explain that every situation is different: your living room is not your bathroom. There is an ideal lamp for every situation.
2. What is in the spectrum
The circadian receptor in your eye is most sensitive around 480 nm. The less of the light falls in the band of roughly 460 to 500 nm, the smaller the signal at the same brightness.
Watch what you base that on. Colour temperature in kelvin is a rough guide: 2000 K is better than 4000 K, but two 2000 K lamps can differ quite a lot in what sits below 500 nm. The reliable information is the spectral curve, or the melanopic EDI. If you get neither, the lamp simply has not been assessed on this point. You can see the curve as an image on our product pages, for example for the Night Glow red night light.
3. Where it hangs or stands
The circadian cells are not spread evenly across your retina, and light from below reaches your eye differently than light straight in front of your face. In practice: a light low to the floor, with the source shielded so you never look straight into the LED, gives less of a signal than the same light at bedside table height.
Indirect light (against a wall or ceiling, or behind a diffuser) is better for the same reason than a visible point of light.
4. How long the light is on
Duration counts on its own. The PNAS study by St Hilaire and colleagues (2022) even shows that spectral sensitivity changes during an exposure: in the first quarter the ordinary cones play a big part, after which melanopsin takes over.
That matters for a night light that stays on all night, because then you are in the range where melanopsin dominates and the choice of colour counts more. For a light you switch on for two minutes, the total amount of light counts relatively more.
What to look for on a product page
| What sellers list | What it tells you | What you want to know instead |
|---|---|---|
| Wattage | Power consumption | Nothing about light output or spectrum |
| Lumen | How much light your eye sees | Melanopic EDI at the distance you use it |
| Kelvin | Rough indication of colour | Spectral curve or share below 480 nm |
| “Blue light free” | A marketing term without a definition | Measured emission in the 460 to 500 nm band |
| “Circadian friendly” | Same | Melanopic DER |
There is no legal definition of “blue light free”. A manufacturer can use the term without giving a number. So always ask about the measurement behind the claim: which instrument, at what distance, and whether you can see the report.
A common misunderstanding
“Red light is safe, so the brighter the better” is not true. Red light is much less effective at suppressing melatonin than blue, but at high enough intensity the effect is not zero. Hanifin and colleagues showed in Chronobiology International (2006) that at equal photon density there was clear melatonin suppression at 460 nm and small reductions at 630 and 700 nm.
So red is a good choice, but not a free pass to turn the light up. That topic is covered in more detail in the article on red light in the evening versus dimmed white light.
What we do not claim
- A night light does not treat sleep problems. Ongoing insomnia belongs with your doctor, not just with your choice of lamp.
- Less melatonin suppression does not automatically mean better sleep. The link is less direct than it seems, other things can be going on, and the study above did not find it for every outcome measure.
- The studies mentioned were done with young, healthy adults in laboratory conditions, not with a night light in a bedroom.
Sources
- Schöllhorn et al., Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness, Communications Biology 6:228, 2023
- St Hilaire et al., The spectral sensitivity of human circadian phase resetting and melatonin suppression to light changes dynamically with light duration, PNAS, 2022
- Hanifin et al., High-intensity red light suppresses melatonin, Chronobiology International 23:251-268, 2006
