The UV detection methods are amongst the most sensitive means of detection available for thin-layer chromatography. Substances fluoresce brightly on a dark background in long-wave UV light at 366 nm. This method demands high light density. It is important, in order to increase the contrast, that the visible portion be filtered out by means of a special filter. If the TLC plate contains a fluorescent indicator then at 254 nm the substance spots appear as dark spots against a bright fluorescent background. White light is required for colou- red chromatograms.