Don't Frighten Children

Telling a child that monsters wait in the dark is an easy way to scare them, and it misses a chance to explain what's really going on. Vision changes a lot in very low light. Put a small night light on before bed. Later, when you wake in the middle of the night, your eyes will have adjusted, and you'll be able to make out shapes, though only in grays, the way old black-and-white movies looked, with soft, fuzzy edges.

Familiar things turn strange under those conditions. An object you'd recognize instantly in daylight, or with the lamp switched on, becomes hard to place. That shape in the corner might read as a monster right up until you flip the switch, and then it's a coat, a chair, something ordinary. A night light helps you move around without tripping, but it doesn't pour out anywhere near the amount of light of a regular bulb, let alone the sun coming through the window.

Here's the part that's actually physical. At the back of each eye, in the retina, you have two kinds of receptors: rods and cones. One kind does its best work in bright light, the other in dim. Cones are the smaller group, and they handle detail and color with a lot of precision, since each cone reports to its own nerve. Rods outnumber them but give you a blurrier picture, because many rods feed into a single nerve.

So it makes sense that the dark feels eerie. A child who gets curious about what the eyes can and can't pick up in near-darkness has less reason to be afraid of it. Keeping lights on all night carries its own cost, though. Melatonin, the hormone your body needs to fall and stay asleep, isn't produced when a room is lit instead of dark, and plenty of small glowing things we leave running in a bedroom can disrupt sleep with only a faint amount of light. There are guides online that rank which kinds of light interfere least with melatonin.

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