Moths and other night-flying insects often exhibit positive phototaxis, an automatic movement toward a light source. Understanding that light color, determined by its wavelength, significantly affects a moth’s visual system is key to reducing their presence around outdoor lighting. By manipulating the light spectrum, people can diminish the attraction of moths to their homes and yards.
How Moths Perceive Color and Light
Moths possess compound eyes, highly adapted for detecting light in low-intensity environments. Unlike human eyes, which rely on three types of cone cells, a moth’s vision is shifted toward shorter wavelengths. This spectral sensitivity means they are highly attuned to light in the blue and ultraviolet (UV) ranges. Moth eyes typically have three types of photoreceptors sensitive to green, blue, and UV light, with peak sensitivities near 525 nm (green), 440 nm (blue), and 355 nm (UV). Their ability to perceive UV light, which is invisible to humans, is important for navigation and foraging.
Identifying Colors Moths Actively Avoid
The colors moths “hate” are not actively repellent but are those they can barely perceive or that do not stimulate their visual system. These long-wavelength colors fall outside the highly sensitive UV/blue range. The least attractive colors are deep amber, red, and the longer wavelengths of yellow. Red light (620 to 750 nanometers) is virtually invisible to many moth species. Lights emitting in the yellow and amber ranges (above 570 nanometers) are less stimulating to their UV and blue photoreceptors, minimizing the visual signal that would otherwise draw them in.
Why Moths Are Drawn to Certain Lights
The attraction of moths to light is largely understood as a navigational error rather than a direct attraction. Moths evolved to use distant celestial light sources, like the moon, for orientation. The moon’s parallel light rays allow a moth to fly a straight line by keeping the source at a constant angle relative to its body. Artificial lights are close and radiate light in all directions, disrupting this system and forcing the moth into a spiraling flight path toward the source. Since moths are most sensitive to short-wavelength light (UV, violet, and blue), any light source rich in these wavelengths, such as white or blue-white LEDs, is particularly disruptive and attractive.
Practical Application of Light Color for Deterrence
Applying this knowledge allows for effective light selection to reduce insect congregation. The recommended solution for outdoor lighting is to use warm-colored lights that filter out attractive short wavelengths. Yellow-specific “bug lights” or filtered LED bulbs emit light predominantly in the yellow-amber range (570 to 590 nanometers). High-pressure sodium vapor lamps, which have a characteristic yellowish-orange glow, are also effective because their output concentrates in longer, less attractive wavelengths. When choosing LED lighting, select bulbs below 3000 Kelvin for a warmer, yellowish light; fully shielding the fixture directs light downward, preventing spillage and limiting the visual reach that attracts moths.