Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 31/05/2013 13:06:23
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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?
Asked by Are streetlights affecting nature?
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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 don’t put out the right spectrum of light.
Hannah - So, streetlights don’t emit the correct wavelength of light in nanometres to boost photosynthesis in plants by much. In which case, what's causing Gerald’s 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, it’s 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 – at dawn and dusk, and it’s 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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Hi,
The 'official' response stated that High Pressure Sodium lights would not affect plant growth. I believe this is incorrect as HPS lights are used widely as grow lights and are considered to be among the most effective during main growth (i.e after seedling stage). I would therefore suggest that powerful HPS lights could affect growth.
Furthermore it was stated that LED lights would not be of any benefit to plant growth. I believe this to be incorrect too as LED grow lights are also becoming common and are reported to be quite effective.
Perhaps this should be corrected?
Jon
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It certainly isn't a lot of fun for moths which think they're navigating by the moon and end up going round and round a light instead. Ten years from now we'll hopefully be able to get rid of all these lights as everyone will be wearing glasses with built-in night vision.
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The only lighting that does not affect plants is the old mercury vapour, as most of the light output is in the green part of the spectrum, where the eye is most sensitive, and where plants are not photosensitive. They are not used as grow lamps at all, as the plants just wither and die under them unless they also get sunlight. Also have the benefit of a 20 year lifetime as well, but the need to recycle them is the only drawback.
For plants to grow you need red and blue light, as that is what the 2 common chlorophyll varieties are sensitive to. So a mix of high pressure sodium light and metal halide light is commonly used, generally 400W of each per fixture next to each other. For LED lighting you will not save much power wise, as you need similar power to get the same light levels. LED lighting at high power is not terribly efficient still, you can get similar efficiency from the old lamps with the added benefit of them not blowing up and needing the whole fitting replaced every 2 years. That is common on the LED road lighting, they tend to fail after 2-3 years, and rather than change a low cost lamp you replace the whole fitting instead and toss it into the bin. That is not terribly good, as the lamp is cheap and the LED fittings are very expensive.
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Sean, that's not true. I grew a cheeze plant very successfully in a dark corner of my hallway under a low pressure mercury lamp. It had lush green foliage and reached 6ft under a single 80W spot lamp. The lamp came from a garden centre, sold as a 'daylight bulb'. Eventually it was the lamp that faded first, the output dropped too much and after 30 years the bulbs were not available, so I replaced it with daylight CFL lamps, which also worked.
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