There have recently appeared articles1 about the "Westinghouse purple X" light and its use as a substitute for the Wood light as a fluorescent agent for tinea capitis. As with any new medicament or physical agent, after enthusiastic welcome and application its limitations quickly begin to appear. The limitations of the "purple X" light give it a clinical use that is of real value, because of the different treatment methods needed for two different fungous infections of the scalp.
The "purple X" light has been hailed as a cheap and simple substitute for the Wood light. In my experience this is not so. The "purple X" light does give fluorescence in infections caused by Microsporon audouini and is entirely adequate for the control examination of that infection. In tinea capitis caused by Microsporon lanosum there will be fluorescence under a Wood light but not under a "purple X" light.
O'FARRELL NM. DIFFERENTIATION OF MICROSPORON AUDOUINI FROM MICROSPORON LANOSUM BY FLUORESCENCE. Arch Derm Syphilol. 1948;57(5):919. doi:10.1001/archderm.1948.01520180136016