Question of the Week

How do street lights affect nature?

Thu, 30th May 2013

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Question

Are streetlights affecting nature? asked:

Gerald McMullon: Chatteris has just replaced all their older street lights. They also removed 10%. The new lights are on taller posts, casting white light further than the older amber lighting. The light has been so bright that my tulips grew leaning over to the new lamp at the front of a neighbour's garden. It took several days of bright sun for them to stand erect.

 

So how does new artificial light impact nature?

Answer

Hannah - So, how does streetlights affect plant growth?

Alex Summers - I'm Alex Summers. I'm the Glasshouse Supervisor at Cambridge University Botanic Gardens. Plants require light to photosynthesise and they require two parts of the light spectrum. They require it at between 400 and 450 and 650 and 700, whereas from my understanding a high pressure sodium lamp works between 570 and 650. So, in reality, the light spectrum put out by a high pressure sodium lamp is probably unlikely to massively affect plant growth. LED lamps which are becoming increasingly common in lots of lighted equipment, we can't use at all in plant growth because they donít put out the right spectrum of light.

Hannah - So, streetlights donít emit the correct wavelength of light in nanometres to boost photosynthesis in plants by much. In which case, what's causing Geraldís tulips to change their direction?

Alex Summers - I would probably say what Gerald is seeing is the tulips tracking the sun. So, as we come more into summer and the sun comes higher in the sky, itís more likely that what you're seeing is that tulips tracking from late winter and spring where the sun being low in the sky, to the sun moving to a higher point within the sky as spring turns more towards summer.

Hannah - But are there other ways that streetlights can affect nature?

Richard James - I'm Richard James and I work in the RSPB's Wildlife Enquiries Department. I think that the most obvious is the sound of birds singing in the middle of the night, particularly robins. Birds generally sing in low light levels Ė at dawn and dusk, and itís thought that the artificial light can actually mimic those low light levels found in the early hours and triggers the birds to sing in the middle of the night. Another relatively common sight is bats feeding on insects around streetlights. Insects are attracted to the lights and bats come along and feed on them.

Hannah - And do the new stars streetlights impacting nature in a different way?

Richard James- There's currently very little evidence that streetlights are having a significant negative impact on our wildlife. However, I have read recently that scientists are concerned that moths are more strongly attracted by brighter white light that has replaced the traditional orange glow from the streetlights. And so, these insects are becoming exhausted because they're spending longer periods flying around the lights, rather than mating or searching for food. And it can make them more vulnerable to predators too.

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