Can I check for black mold with a black light?

Written by chris anzalone
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A black light is a fluorescent bulb that emits ultraviolet radiation. Though you may find them in party supply stores, they serve some practical purposes. Black lights can detect counterfeit money, locate fingerprints in a crime scene and even detect mould inside of a home.

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How It Works

When you shine a black light in the presence of a mouldy surface, the mould should emit a yellow, or sometimes greenish yellow, glow. The ultraviolet light from the fluorescent bulb causes the otherwise dull mould spores to appear bright and almost neon in appearance. Even if you cannot see the mould spores on the household surface -- for instance, sometimes mould can hide in thick, wet carpets -- you may still see the telltale glow when shining the black light.


A black light can detect the presence of mould, but it cannot tell you the type of mould. Since over 400,000 types of mould exist, you will need a more expert analysis to tell if your mould is toxigenic (capable of causing disease), pathogenic (capable of causing infection) or simply allergenic (dangerous only to allergy sufferers). In addition, while a black light does serve as a rapid mould detection tool, it is not reliable 100 per cent of the time, according to a University of Florida Extension report.

Why Black Lights Can Fail

A professional mould inspection is always your best course of action, although a black light can help you determine the possible presence of mould. Before using it, however, you should know that other substances always emit a green or yellow glow, and so even if you notice the glow, it may indicate a different fungus or a different substance entirely. If you do not spot a glow indicative of mould, you may still have mould hiding deep within a household surface, like a wall board, for instance. If you notice other signs of mould, like a musty odour, contact a mould specialist.

Proper Inspection

While a black light should never be your only means of inspection, it can help you to quickly spot hidden mould, or to verify suspected mould. For instance, if you notice dark patches on a carpet, and you want to determine whether the patches consist of mould or simply dirt, hold up the black light. Dirt will not glow, but mould will. Carry your black light to any location where you suspect possible mould, like along moist walls, throughout your basement, over flooded carpets and into the attic.

Where to Buy

You can find black lights at hardware stores and home improvement stores. Just ask for fluorescent bulbs or UV lights. You can also find black lights at party supply stores and DJ supply stores.

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