This time of year, on my commute home through the forest, I need a bright headlight for me and other humans (and some wildlife) to stay safe. However, research suggests that night lights kill many insects:

From the article in The Guardian:

LED lights also offer hope as they can be easily tuned to avoid harmful colours and flicker rates.

My headlight is a Busch + Müller Lumotec IQ Fly Premium Senso Plus LED. How can I tell if this LED is (relatively) insect-friendly?

This is probably more of an issue for car drivers than for bicyclists (I don't think I'm killing that many insects at 20 km/h), but the question would be relevant for both, and also for anyone else who needs to use light outdoor.

  • It's hardly relevant for car drivers - with their speeds is not an issue of being attracted to the light, but being at the wrong time in the wrong place (in front of the car). Even with your bike speed I'm not sure the numbers you kill are relevant. – user2451 Nov 22 '19 at 16:15
  • @JanDoggen The linked article disagrees for the case of cars, and suggests that insects are in fact attracted to roads due to the many headlights there. do you have evidence to the contrary? – gerrit Nov 22 '19 at 16:36
  • Why the downvote? – gerrit Nov 22 '19 at 16:36
  • @JanDoggen To clarify; I don't think they mean an individual car in an otherwise deserted area is going to kill lots of insects due to the lights. But a busy highway has lots of cars, and it passing through an otherwise dark area, the way I understand it is that the insects will be attracted to the general vicinity of the road due to the large number of lights there. – gerrit Nov 23 '19 at 12:47

First, the amount of light you use is (close to) the minimum for the task - you're already doing far better than most. It may still be a concern as you seem to be in an area that's otherwise dark, but a good bike light is mounted fairly low and pointing down (equivalent to shading the light appropriately as mentioned in the Guardian article).

The article mentions that LEDs allow better wavelengths to be selected, but also say that blue-white lights are worse than others. A white LED is a blue LED with a yellowish broadband phosphor coating, so it's fairly strong in the blue region of the spectrum, which is less good. However to see where you're going and avoid hazards you need a broad spectrum. To test, and don't do this while riding, set up a view of something like a branch covered in green leaves, lying on a dark road, and illuminate that with your red rear light. You'll find it's much less visible with this narrowband source than with a white light. Switching to yellow or green just means other hazards disappear. You can get round this by using multiple wavelengths, but may well need more total light than with your well-designed white LED lamp; you'll certainly illuminate a bigger area. The journal paper and the citations in it state that several diverse species of insects are more sensitive blue and green light than to longer wavelengths. As you need these wavelengths to see well enough to ride, a wavelength-optimised source isn't a solution.

LED bike lights flicker (too fast for human perception) when run at reduced power (and sometimes at full power). This is because the power output is regulated by pulse-width modulation. Potential Biological and Ecological Effects of Flickering Artificial Light, Inger et al., 2014, cited in the paper linked in the question goes into some detail on flicker frequencies. Unfortunately it's a little old when considering the prevalence of LED sources, and concentrates on lower frequencies, however it's reassuring as figure 1B shows a few hundred Hz as the upper limit for insect sensitivity to flickering. A rough estimate of the flicker rate of my bike light is a few kHz, which is too fast to be an issue. This estimate is based on the streak length of water drops thrown off my front wheel, my speed, a lot of assumptions and mental arithmetic; I really ought to check with a photodiode, but this is a reasonable (or even low) value for LED PWM.

The methodology for assessing whether a given light is problematic is inherently a little complex, but as a rule of thumb, dimmer, redder, more specific to the need, and either steady (DC incandescent) or flickering at >1kHz are all good.

The paper also states that some modern LED fixtures emit ultrasonic frequencies that could have compounding effects on insect fitness. This would be due to switch-mode power supplies, used in most high-brightness LED lamps as they're more efficient than linear regulation. One small source passing by fairly quickly isn't going to be much compared to LED streetlights.

  • This isn't quite right. Some people can see LED flickering and are extremely bothered by it. One reason incandescents continue to be popular. – InterLinked May 26 '20 at 19:01
  • @InterLinked flicker (existence and frequency) is a property of the driver not the LED itself. It's a minor point but a crucial one. Flicker at human-observable frequencies is far more likely on mains-powered lights with cheap drive circuits than pulse-width modulation of DC-powered emitters. – Chris H May 26 '20 at 19:05
  • Right, but in practice most LEDs are powered by AC, not DC, so it's an issue. The people I know who can see LED flickering only observe that with AC powered LEDs. – InterLinked May 26 '20 at 21:05
  • @InterLinked technically that's true in this case as a bike dynamo is really an alternator. Note though that I didn't say "AC-powered", I said "mains-powered", which this isn't unless the OP has a very long cable (mains is fixed at 50 or 60Hz, but the variable frequency of a bike dynamo means the electronics have to smooth as well as rectifying. This isn't perfect as you'll notice at very low speeds. – Chris H May 26 '20 at 21:14
My headlight is a Busch + Müller Lumotec IQ Fly Premium Senso Plus LED. How can I tell if this LED is (relatively) insect-friendly?

It is. The Busch + Müller headlights have a proper light pattern. In contrast to the numerous mainly Chinese bicycle headlights that blind all oncoming drivers / cyclists, due to their high power and the rotationally symmetric light pattern, the German Busch + Müller headlights have a properly designed light pattern.

So, the stray light is very minimal. The headlight mainly illuminates the road.

Not only that, but also the headlight is in motion, so it annoys 1 insect for a very small amount of time. Then, it starts to annoy a second insect, a third insect, etc. Compare this to streetlights that stay in the same location and annoy the same insects all the time.

Edit: let's analyze the insect friendliness of lights:

  • High powered light is less friendly than low-powered light
  • Fixed light is less friendly than a moving light
  • Light that distributes its light everywhere is less friendly than light that illuminates only what is needed
  • Thanks, but your answer is a little bit more specific than I intended. Maybe I elaborated too much in my question on the specific example. But maybe the general question "how can I tell" is too broad? – gerrit Nov 22 '19 at 17:19
  • Do you know anything about wavelength (narrowband, wideband, specific frequencies) or flicker? – gerrit Nov 22 '19 at 20:47

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