Pink lights have recently appeared as a measure against teenage loitering, because they are supposed to highlight skin blemishes. When they were first installed by a resident’s association in Mansfield, UK in 2006, even though many sarcastic views were expressed in media, to the Mansfield residents it seemed like a cheap and doable solution.
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http://news.bbc.co.uk/2/hi/uk_news/england/lancashire/6197652.stm
Blue neon lights were successfully used in public bathrooms and publicly accessible toilets, as a means of preventing drug users from injecting themselves. Because it makes veins harder to see, it is expected that drug users will stop using these bathrooms for the aforementioned purpose.
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Blue lights used in the public toilet in The Hague City Hall; men's toilet
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Blue lights used in the public toilet in The Hague City Hall; women's toilet
further reading:
http://www.theargus.co.uk/archive/1999/02/18/The+Argus+Archive/
http://news.bbc.co.uk/2/hi/uk_news/england/cambridgeshire/3147170.stm