Blacklight

We have already talked about Infrared, so now we will talk about the other side of the visible spectrum, ultraviolet. We commonly refer to ultraviolet light bulbs as black lights but this is a misnomer because the light is not actually black but a deep purple since that is the part of the visible spectrum that is closest to UV. As we discussed before, if we could see infrared, it would be on the top of a rainbow whereas with ultraviolet, it would be on the bottom. In the first decade of the 20th century, Robert Wood created a filter that only allows ultraviolet light to pass through but blocked visible light, the filter was called fittingly enough Wood’s Glass. Murdoch, who create a filter similar to this but about ten years earlier, used his “new source of light” to see blood that was invisible to the naked eye that was cleaned out of a carriage. The problem with blood is that it does not fluoresces under black light so to see the blood you need to be lucky enough and have the a material that fluoresces under black light so that it will create darker regions where the blood is. Despite some historical inaccuracy, a little bit of anachronism is forgivable when you manage to figure out who Jack the Ripper was.

 

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