To pick the best night light for a child’s room, you need to know about the kind of light that can disrupt children’s sleep, or harm their eyes.

What kind of light disrupts sleep?

Blue light is part of the spectrum of white light, as the English genius Isaac Newton (1643-1727) discovered when he shone white light through a prism. As scientists discovered centuries later, it is this part of the spectrum that has special effects on our nervous system.

First, when blue light hits cells in the retina–cells not related to vision, but to regulating our circadian rhythms, or internal clock–it tells our bodies that it is daytime. This message energizes us, which is fine when we want to listen to a lecture, or play tennis, but not convenient if we are trying to relax.

Second, exposure to blue light in the evening, or during the night, tells our body that it is still time to be awake, and pushes our body’s perception of bed-time into the future. That’s why exposure to white light before going to bed is likely to keep you up.

For the same reason, exposure to night lights with white light make it harder to go back to sleep if you get up in the middle of the night.

Third, blue light at night can harm the eyes. At the risk of oversimplifying the mechanisms involved in sleep, the hormone melatonin, released daily by the pineal gland, is most abundant at night. Melatonin’s presence in the retina makes us more sensitive to blue light. Consequently, at night we are most attuned–and vulnerable–to blue light.

How can you get night lights that minimize blue light?

If your children tend to get up during the night, use amber-colored nightlights rather than white ones. Amber lights will not wake up their nervous systems when they want to go back to sleep. Think lullaby, not fire alarm. CET recommends the nightlight here.

How else can you avoid blue light?

Tone down your computer. To help you and your child keep normal hours, you may want to reduce your exposure to white (full-spectrum) light for two to three hours before bed-time. You can do this by restricting your use of computers and other devices which emit blue light.

Alternatively, you can  install f.lux, a free application which gradually changes the quality of light your monitors and devices give off during the day and night. This will reduce your exposure to blue light during the evening and night.

Try protective eyewear. Amber glasses, like those here, allow you to work under bright white lights without a problem because the glasses filter out the right part of the spectrum. Consequently, these glasses can also help you get to sleep earlier.