They were discussed a lot in 2009 when they were first installed, but since then many people new to Tokyo may be a bit perplexed by the funny blue LED light found on many JR platforms. They were actually installed in order to help stem the terrible suicide rate prevelent in Japan, the theory being the that the calming effect of the blue light will soothe peoples nerves and help disuade them from suicidal thoughts. The really interesting thing about this project is that there was absolutely no scientific backing of the effectiveness of blue lights, nevertheless the railway companies spent a lot of money to have them installed.
I've googled around to see if there have been any actual prof of the blue lighjts' effectiveness, and one article on the web quotes a 2013 study claiming that an "84 percent decrease in suicides at stations with the blue lights." This is pretty impressive! Frustratingly the study doesn't really postulate why they had such great results. Some articles have critisized the lights as simply a human relations ploy by the railways to seem more sympathetic.
My own hypothesis on the effectiveness is that since everyone basically knows why the lights were places at the stations, somebody who is comtemplating suicide may feel some awareness of the need to reach out and do something to help. If anyone has any other theories regarding this, I would love to hear your comments.