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Returning to the subject of LED & other forms of lighting, I hope it will be useful to point out a large misunderstanding that has persisted for a long time. This is the belief that alpines and other plants grow more compactly in the wild than they often do in cultivation due to being exposed to higher levels of UV radiation. This is actually not true. In his bulb log last November http://www.srgc.org.uk/logs/logdir/2014Nov121415787177BULB_LOG_4614.pdf Ian showed the new LED system that Gothenburg is trialling and said that they were "high in UV" for healthy growth. If you check the spectrum of the lamps used on the company's website, you will see that actually these lamps cover the range of 400nm to 735nm - which encompasses the photosynthetic spectrum but not the UV. In fact these lamps don't give out any UV light at all.Science does not yet fully understand all the ins and outs of the specific effects of various wavelengths of light on growth, but experiments on alpines have shown that levels of UV light do not affect the stature of the plants. In fact, like most things, UV can damage plant tissue just as it can damage your skin if you stay out in the sun too long. Experiments show that most plants actually reflect the majority of UV light that falls on them in order to protect themselves from damage. And the experiments also show that of all groups tested, Alpines reflect the most UV (more than 90%).As well as experiments, observations in the wild also point to the fallacy of the idea that it is the UV keeping plants compact. For example, many arctic and sub Antarctic plants inhabit misty coastal ranges where they receive very little UV and yet they are extremely stunted and dwarfed. Also, if UV intensity had a significant effect, you would expect to see latitudinal gradients in the stature of alpine plants, but this does not occur.So what does keep alpines dwarf and compact? While the full story may not yet be in, the evidence all points to LOW TEMPERATURE as the key factor. Our alpines in cultivation grow out of character largely because we cannot keep them cool enough. It is also known that the overall intensity of light (of all the useful wavelengths, but not UV) has a part to play at least for some species.For those who would like to know the references and read more about this, the best place to start is the discussion about all this on pages 114 to 119 of the book "Alpine Plant Life - Functional Plant Ecology of High Mountain Ecosystems" (second edition) by Christian Korner ISBN 3-540-00347-0Paul
Ian's impression was that it was the higher levels of all the spectrum of light, including UV, that was the point of these lights. Either he got the wrong end of the stick as regards the description he was given, or he and the GBG folks are all labouring under a misapprehension!
Hi Maggi,The lights at Gothenburg would still be useful for increasing the day length (especially in their northerly latitude) and the overall light intensity the plants receive and these should lead to improved growth. The operating costs should also be cheaper than traditional grow lights. I would imagine that these are the reasons they are trialling them. Though the 'myth' that UV improves compactness is so ingrained that it would not be a surprise if they were also under that misapprehension.Paul