One of the fastest way to identify feline ringworm is to look for glowing hairs using a Wood’s Lamp or blacklight. A Wood’s Lamp is a blacklight with a UV spectrum 320 to 400 nm wavelength. Your blacklight should have a similar wavelength and be at least 20 LED.
And before you comment that “only 50% of all ringworm glows,” you should know that the 50% statistic comes from human studies, not feline. According to Dr. Moriello, “a Wood’s lamp examination
is likely to be positive in most cases of M canis infection” and you will see fluorescing hairs in 91 to 100 percent of the cases.
Ringworm hairs do not “fall out,” they break off. And even after the hair has broken off, you should be able to see the ends of the hairs glowing. This can require magnification.
However, not all glow is ringworm. Many medications will glow under blacklight. However, the glow is more yellow than green. And you usually won’t see hair loss on those areas.
Even after the hair falls out, you can see glowing hair shafts. 
