The eye has a third type of cell. And it's the one that runs your sleep.

Background

Until the late '90s, melatonin was assumed to be governed by the rods and cones, the photoreceptors we see with. But that model couldn't explain certain anomalies: blind people with no working rods or cones still kept their circadian rhythms. Something else was catching the light.

What the study looked at

Brainard's team exposed 72 healthy volunteers to different wavelengths of monochromatic light between 2:00 and 3:30 a.m., with their pupils dilated. They measured blood melatonin before and after each exposure to build a full action spectrum, a map of which wavelengths suppress the most melatonin and which barely touch it.

What they found

Melatonin suppression doesn't follow the rod or cone profile. Peak sensitivity sits around 446-477nm, the blue-green band of the spectrum. As the wavelength moves toward red, the ability to suppress melatonin drops off sharply. At long wavelengths like 660nm, suppression is minimal.

What this means for you

The ordinary light you switch on at night to tend to your baby puts out exactly the range that suppresses their melatonin the most. Not because it's "bad light," but because its spectrum includes the blue band that switches the circadian system on. The NeuroSafe™ Light works outside that band. It doesn't switch the system on. Your baby's melatonin keeps flowing.

Study limitations

The study was run in adults, not babies. Babies have a clearer lens that lets more blue light reach the back of the eye, which suggests their system is even more sensitive. Not less.