I’ve already written a post about whether wearing sunscreen at night was necessary, but in it I focused on the UV light emitted by lightning and computer screens, and came to the conclusion that it wasn’t strong enough to harm skin. Thus, sunscreen wasn’t needed. But what about moonlight?
Surely, most of us won’t spend many hours outside in the middle of the night, but now that the days are shorter and the sun sets earlier, leaving its place to the moon already in the mid-afternoon, do we need to wear “moonscreen” to protect our skin from its light, when we’re out running errands or taking our dog for a walk?
The short answer is no. The moon doesn’t emit any light of its own, but only reflects the sunlight that hits it. But can this sunlight, when reflected to the earth, damage our skin? Again no. Dr Neil Schultz explains why:
“The diameter of the sun is slightly greater than 400 times the diameter of the moon. So if the moon were a perfectly reflective mirror reflecting 100% of the sunlight that hits it, it could only reflect 1/400th or ¼ of 1% of the sunlight.
But the moon’s surface is a very poor reflector, instead absorbing most of the visible and UV light that hits it… reflecting only 7 to 12% of visible light, and only about 0.7% of UV light… that’s less than 1% of the UV light.
So between the small size of the moon and it’s poor reflectance, only about 1/40 of 1% of the sun’s UV is reflected to the earth… Said another way, 99.98% of the sun’s UV does NOT get reflected. It’s just like wearing a sunscreen that blocks 99.98% of the sun.”
But what about that tiny amount of UV light that the moon does reflect to the earth? There’s no need to worry about it either: it simply gets absorbed by the atmosphere. So, once the sun has set, you can stop reapplying sunscreen. After all, it’s called SUNscreen for a reason.
Have you ever worn sunscreen at night?