It is quite possible that flies prefer one part of the light spectrum more than another part, but to say in the title that they don’t swarm at LEDs is misleading at best.

If you compare an incandescent soft white porch light to a similar brightness soft white led light, you will probably see dramatically more insects at the incandescent bulb. .

There probably are insects that don't perceive the "thinner" spectrum, but generally it (sadly) isn't true.

I have a 405nm laser pointer and it makes certain things (any% titanium dioxide) absurdly bright from fluorescence. So you probably aren’t getting UV from those bulbs, but certainly some IR.

Nope. Blue light just happens to do well at exciting fluorescence in some materials, especially bleached and whitened ones like paper and laundry. 420nm blue light will excite red fluorescence in a ruby. 532nm green will induce BIP in calcite. Certainly no UV present in an upconverted IR laser.

It's not UV.

Note you can make LEDs dim without PWM via constant current drivers, just less efficient as the duty cycle is 100%, they look much nicer though

In those days TV's were big CRT boxes, illuminated by the electron beam which would race across the screen row by row.

A housefly's "refresh rate" on its eyeballs is much higher than that of a human, so the fly wouldn't see an image as we do, but would presumably find it quite relaxing watching the dot of light slowly move across the screen.

However, my mind developed a similar conjecture to your's: what if the common frequencies of PWM occur within a kinetic visual blindspot of insect vision, like human saccades [0] in the novel Blindsight [1], so that insects are not aware of the LED at all?

0. https://www.ncbi.nlm.nih.gov/books/NBK10991/

1. https://www.rifters.com/real/Blindsight.htm#:~:text=%22There...

I think cars became a lot more aerodynamic which makes comparisons difficult.

When I installed a roof rack on my car, it was full of insects after a trip. I don't know how the amount of insects would compare to decades ago though.

As a counter-anecdote, I bought a house recently and the back yard is basically uninhabitable all summer due to insects. Insects may be less prevalent along some roads due to better drainage.

Another point I'd make is that there's no reason to think insect life should be stable across 30-40 years. Insects are not people. Even aside from climate change, insect population is very dependent on weather patterns.

There are bugs. You photographed bugs. Maybe more than you would have without lights at all, maybe about the same.

Also better lights don’t necessarily mean perfect lights. We do lots of things to reduce harm. Unfortunately sometimes we do them too much and conserve a significant fraction of the original harm by increasing demand.

Speaking of things being wrong...how can you come to this conclusion? There are many beaches where turtle hatchlings get confused by all of the lights on land where they crawl away from the ocean instead of towards it. Land is so bright, that the vast majority of humans can no longer see the night sky. So again I ask, how do you come to the conclusion that land is darker than the sky?

Insects eyes are biologically very different.

With LED lighting, if you have lots of spot lights in the ceiling and and open door, you’ll likely find that the light leaving the house is a bath of reflection from different sources inside the house and that likely cancels out the worst of the flicker.

They didn't say no bug ever goes to any led light.

I guess it is most likely some combination of the above, but if there's any evidence it would be a neat reframing

We use UV/IR combo Flame detectors at work for this purpose.