3 November 2026
Remember when you used to encounter swarms of insects around outdoor electric lights? Their well known attraction to outdoor lights is used by entomologists and moth lovers to conduct insect surveys. All you need is a light and a white sheet to see who’s flying at night.
Nowadays, if you want to attract insects, you have to be picky about the light you use. As everyone changes over to LED lights, we humans see the color difference but we can’t see the crucial difference in insect attraction between incandescent and LED.
Our guide Roland Rumm on the WINGS Veracruz trip described the change in insect behavior with the switch to LED lights. His family has an outdoor dining space that is well lit with artificial light. As a child he loved to watch the geckos climb to the lights and eat the insects.
In recent years the family changed over to LED lights and the geckos disappeared. Were the geckos gone? No. But far fewer insects were attracted to the LED lights so the geckos had no reason to show up.
In 2024 the BBC wrote about Why insects are drawn to artificial light at night:
Flying insects use moonlight to navigate. Since the moon is always above them, they orient themselves so that the light shines on their backs. That’s how they stay upright in flight.
Moonlight contains ultraviolet (UV) and infrared wavelengths because it is merely reflected sunlight. Insects cue on UV, believing it to be the moon. When artificial lights transmit UV they look like moonlight so insects orient their backs to it. Consequently they circle the light and even flip upside down when the artificial light is pointing up to the sky!
Incandescent lights transmit UV but LEDs do not. Insects are far less attracted to LED.
“Incandescent lights transmit UV” is true, but confusing.
You’ve probably seen statements that incandescent light transmits “virtually nil” ultraviolet light. Virtually nil means the amount is very small and not harmful to humans. However, insects see UV and our “virtually nil” amounts attract them.
How much ultraviolet do incandescent lights transmit?
This graph provides background for the next one by showing ultraviolet wavelengths range from 100 – 400 nm and visible light ranges from 400 – 700 nm. (graph was created to illustrate Far-UVC which is used to sterilize equipment.)
In 2018, Tarun Kumar et al examined the Safety of Light Emitting Diode (LED) Based Domestic Lighting in Rural Context. Their study measured and graphed all wavelengths emitted by four sources of light: two LED lights (with & without polymide film to block a spike in visible blue light), a 100w incandescent bulb, and sunlight.
We’re talking about ultraviolet so I marked the UV emissions range, 100 to 400nm, in pink. Sunlight (green graph) has a lot of UV in it. Look for the || symbol which points to the 100w incandescent “virtually nil” ultraviolet emission. Two lines, both LEDs, are zero in the UV range then climb in the visible range.
If you’re curious about infrared (greater than 700 nm), notice that the 100w incandescent produces more incandescent than sunlight.
Insects are far less attracted to LED.
In 2016 scientists at the University of Bristol, UK ran experiments to compare insect attraction to four types of light: Incandescent (tungsten filament), Compact fluorescent, “Cool-white” LED and “Warm-white” LED.
We conducted field experiments to compare the relative attractiveness of four commercially available “domestic” lights, one traditional (tungsten filament incandescent) and three modern (compact fluorescent, “cool white” LED and “warm white” LED), to aerial insects, particularly Diptera. We found that LEDs attracted significantly fewer insects than other light sources, but found no significant difference in attraction between the “cool” and “warm white” LEDs. Fewer flies were attracted to LEDs than alternate light sources, including fewer Culicoides midges (Diptera: Ceratopogonidae). Use of LEDs has the potential to mitigate disturbances to wildlife and occurrences of insect-borne diseases relative to competing lighting technologies.
— Experimentally comparing the attractiveness of domestic lights to insects: Do LEDs attract fewer insects than conventional light types?
Here’s what they found. NOTES: CFL = Compact fluorescent, FIL = incandescent (the old lightbulb), LEDC = LED cool white, LEDW = LED warm white light.
Typically LEDs do not emit UV light and are more energy efficient than traditional technologies. Electrical energy is converted almost entirely into electromagnetic (EM) radiation within the range of the visible light spectrum (400–700 nm) and therefore not wasted on producing wavelengths of light invisible to the human eye, that is, UV and infrared (IR). Thus, LEDs are less attractive to many insects than lights which emit UV light.
— Experimentally comparing the attractiveness of domestic lights to insects: Do LEDs attract fewer insects than conventional light types?
So that’s why there are very few bugs circling LED lights at night.
According to the BBC, this trait of LEDs is a good thing because incandescent (UV) artificial light at night distracts insects so much that they don’t reproduce, don’t feed, etc. Thus artificial light is considered a major reason why insect populations have declined. See: The impact of artificial light at night on nocturnal insects: A review and synthesis.