Question of the Week Podcast

Question of the Week episode

Thu, 30th May 2013

Do street lights affect birds and plants?

Streetlight (c) Dave Ansell

We find out if street lights are affecting plants and birds. Plus we ask how high can a mountain be here on Earth?

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In this edition of Question of the Week

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  • How do street lights affect nature?

    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 f...



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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 jonwestcott, Fri, 31st May 2013

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. David Cooper, Fri, 31st May 2013

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. SeanB, Fri, 31st May 2013

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.

Mikey63, Fri, 19th Jul 2013

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