Warm it up

There’s a distinct problem with light at night. We all know how it can annoy us humans and keep us awake, but the problem is felt by millions, even billions of others, not just us.

The latest figure I could find suggested that in a square kilometre of sky, at all times, there are billions of insects. So it’s no surprise that when you turn the light on at night some of them will be attracted.

But recently it was suggested that if we can’t turn off the lights we should do something to mitigate this mass attraction that we have created. The angle thrown at me was actually that we should be attracting insects to areas where bats can feed, but we have to be really careful about bats, morally and legally. Not sure the insect lovers amongst us would agree with this proactive feeding approach, if we were careful with our lighting bats and insects wouldn’t be impacted at all by our human needs. They don’t need our help, clearly they need protection from us as a species.

Okay, perhaps some explanation. Most insects are attracted to light, some, like the night flying bee and moths, can have particular problems. Most insects are phototactic. Phototaxis is an organism’s automatic movement toward or away from light. Moths for one are positively phototactic, they move toward light. While there is no simple explanation for this, there are some interesting ideas, such as navigational confusion as our lantern imitates the moon and so on. But no matter the real reason, artificial light is certainly a problem.

Moth and light image
Moths attracted to a wall light

Moths, like most insects are more sensitive to some wavelengths of light, most towards the ultraviolet end of the spectrum. So a white light, particularly that containing a lot of blue or UV will attract more moths than a yellow light. Yellow actually is a wavelength moths don’t respond to very well.

Research in the Tirol backs this up. Over a number of light sources the research showed that Metal Halide light sources attracted on average 310 insects per night, compared to the best LED at just 46. (In a square kilometre of dense road network, average 25m lantern spacing leads to 1600 road lanterns, assuming metal halide lamps, that’s half a million attracted insects per night, still leaving billions for the bats). Interestingly the original Low Pressure Sodium lamps were omitted from the trials, these being considered unsuitable as a technology now, but they would have an even lower attraction rate.

6000K LED attracted 75 insects per night per luminaire, 3000K just the 46, and this finding was used to justify a change in lighting policy. Again be careful and use only warm colour temperature LED as cold LED is bad for insects and therefore bad for bat populations.

Therein lies the problem. We know that light offers many benefits, but that there are often negative effects and some choose to focus on just the one point of view. Light increases safety on the roads and the feeling of security in residential areas, but it uses energy and demands care in design. It’s a balance we find difficult because we value one thing over another and we don’t always agree on the balance point. The balance has to be found for bats and insects too. If we install UV based white light, it will attract more insects. But it is clear that this research suggests LED is not the problem, in fact LED attracts at worst only 25% of the insects of the worst offenders. Warm versus cool LED is not really worth arguing over compared to LED versus Metal Halide; though personally I would argue for warmer light sources outdoors for reasons of sleep, glare and light pollution. We could argue that LED not only saves energy and reduces light nuisance to humans, but also is better for other inhabitants including insects and bats. I’m assuming here the luminaire is well designed, well placed, is on to the level we need, when we need it etcetera, etcetera.

There is always another point of view too. Whilst the light might keep you awake at night, it really shouldn’t. You really shouldn’t have to replace your curtains due to bad lighting design. That same light affects all the flora and fauna around it. The light spectrum that is right to reduce impact on insects will be different for other species. The light intensity will always impact flora and fauna… they can’t draw the curtains.

By maclighter

A Chartered Engineer in Lighting, though trained in mechanical, with 30 years lighting design, technical, manufacture and marketing experience. A trusted mentor, designer, emergency and DIALux trainer, speaker and past president of the Society of Light and Lighting. Get in touch if I can help you out.