Mould spores can sometimes be detected under black light because certain species fluoresce under ultraviolet (UV) light. While not all moulds glow, certain organic compounds within some mould spores emit light when exposed to UV rays, making them appear as spots or patches that range in color from yellow-green to blue, depending on the mould type and the surface it's on.

How It Works.

Fluorescence: Some moulds produce metabolites and compounds (like NADH and riboflavin) that naturally fluoresce under UV light, causing them to "glow" when exposed to black light.

Spotting the Spores: Mould spores and colonies often grow in damp, dark, or hidden areas, so using a black light can help locate potential mold growth where it isn’t easily visible.

Varied Colors: The colors seen under black light vary because different moulds fluoresce at slightly different wavelengths, creating different hues.