Adding lamps, string lights, and other outdoor lighting is a great way to make your yard and porch look charming and inviting, and security lights can of course be important for safety. The problem: If you use the wrong kind of bulb—i.e., ones that emit a cool, white light—you’ll attract nocturnal insects, which will fly around your lights until they’re zapped and killed, says Doug Tallamy, TA Baker Professor of Agriculture in the Department of Entomology and Wildlife Ecology at the University of Delaware. Tallamy urges everyone to use yellow bulbs in their outdoor lights, instead of white ones, as a way to help preserve insect populations.

Why Yellow Bulbs Don’t Attract Insects

Nocturnal insects evolved with the moon as their primary light source, and they naturally orient themselves so that light is above them and darkness is below them. This is called “dorsal light response,” Tallamy explains, and it’s why insects don’t fly upside down. The moon emits light in the cooler, white spectrum (about 4100 Kelvin). When we use bulbs in that same spectrum, insects are drawn to the light as though it were the moon. In line with their dorsal light response, they try to keep the artificial light at their back, so they get trapped flying around the bulb in circles, until eventually they fly too close and get killed.

Yellow wavelengths, on the other hand, don’t correspond to moonlight and are therefore less attractive to insects, Tallamy says. So nocturnal bugs will likely stay away from your bulbs altogether.

How to Find the Right Outdoor Bulbs

You can easily find yellow bulbs online or at your local hardware store. Look for a “bug light” label, or for a warmer color temperature (around 2000 Kelvin). LED bulbs are preferable to incandescent ones, Tallamy adds, because they’re far more energy efficient.

As a bonus, these warmer lights offer a cozier vibe than harsher white ones, so you and your guests will likely find them more soothing as well.