Short answer: yes, at the same brightness red light gives a much smaller circadian signal than white light. But the advantage is not unlimited: at high enough intensity, red light suppresses melatonin too. That means very dimly lit white light can come out better than bright red light. The comparison only holds when you look at both at the same brightness.
The underlying mechanism is covered in the article on which light disturbs your sleep and which does not.
Why red has the edge
The circadian receptor in your eye contains melanopsin, which is most sensitive around 480 nm. Red light at 620 to 700 nm is far from that, on a part of the curve where sensitivity is orders of magnitude lower. Warm white light, on the other hand, always contains some short wavelength emission: however warm it looks, there is blue in it, otherwise it would not look white.
At the same illuminance in lux, red light gives a much lower melanopic EDI than white light. That is the whole advantage, and it is a real one.
Why the advantage has a limit
For a long time it was assumed that light above 600 nm does not affect the circadian system at all. That goes too far.
Hanifin and colleagues looked into this directly and published it under the title High-intensity red light suppresses melatonin (Chronobiology International, 2006). At an equal photon density of 1.9 × 1018 photons per cm², light at 460 nm caused clear melatonin suppression, while light at 630 and 700 nm caused small but measurable drops in melatonin levels.
So the conclusion is not “red causes no suppression” but “red is weak”. And weak times a lot is still something. If you have a bright red lamp on all evening, you can still end up in an intensity range where there is an effect despite the favourable wavelength, although always less than with white light.
Limits of this study. It used monochromatic light at very high photon densities in a lab; the measured drops at 630 and 700 nm were small. The result shows that sensitivity is not zero, not that a red reading lamp is a problem.
The fair comparison
You cannot answer “red or dimmed white” without the brightness. Three situations:
| Comparison | Result |
|---|---|
| Red and white, same lux | Red clearly better |
| Bright red versus very dim white | Can tip in favour of the dimmed white light |
| Red, dimmed to the same low level | The best of the three |
The practical lesson: do not treat red light as a free pass. It lowers the signal per lumen, but it does not replace the dimmer.
Brightness differs per home and per room
You often do not need to install dimmers. Our lamps come in different wattages depending on the fitting. For some situations a lamp is too bright, for others not bright enough. In the living room you often come from brighter spaces and people usually want a bit more light. If your living room is also large, with lots of dark surfaces like walls, curtains and floors, a 7 watt lamp is sometimes not enough. In a much smaller bathroom, often with light reflective tiles, a 7 watt lamp just before bed is far too much. As an example, in my bathroom, which is not small, I use the Night Glow battery night light on setting 1 for brushing my teeth, and the Wall-E sensor light when I only need the toilet.
Conclusion: match the lamps to your rooms, their size and when you are in them. Early in the evening a 7 watt E27 amber lamp can give the most light, and in the bedroom you probably want a red dimmable version on the lowest setting.
Red light in the evening is not the same as red light therapy
These two get mixed up regularly. A red reading light or night light is lighting: weak, so you can see without stimulating your body clock more than needed. Red light therapy with LED panels works with intensities many times higher, aimed at the skin, with a completely different goal.
It is exactly at those high intensities that Hanifin’s result matters: using a bright red panel in the evening is, in terms of light dose, fundamentally different from having a red night light on. If you do both, they add up.
In practice
- Choose red or amber over warm white when the brightness is similar.
- As little light as possible. The choice of colour does not fully replace dimming.
- Ask for the spectral curve. It shows at a glance whether there is a second peak in the blue, which is the case with some lamps that look red. Ours are published on the product pages.
Sources
- Hanifin et al., High-intensity red light suppresses melatonin, Chronobiology International 23:251-268, 2006
- St Hilaire et al., The spectral sensitivity of human circadian phase resetting and melatonin suppression to light changes dynamically with light duration, PNAS, 2022
- Schöllhorn et al., Melanopic irradiance defines the impact of evening display light on sleep latency, melatonin and alertness, Communications Biology 6:228, 2023
