I've heard anecdotally that mold will glow green under a black light (UV light). Is this true?

There's a room in my house with a musty odor, and I'm trying to determine the source of the smell. There's a substantial amount of unpainted wood - here is a sample of what it looks like under an ultraviolet light:

Possible mold in wood

(Photo specs: 1s f/4.5 exposure under 2 48" 36W T8 UV lamps.)

Does this indicate mold growth in the wood? (Freshly cut wood exposed to the same UV light does not reflect the same green-yellow color.) I have tried cleaning the surface of the wood with mold/mildew cleaner, to no effect. My understanding of mold growth is limited and I'm having a hard time coming up with reliable information about it.

  • Did you ever confirm if this is mold... I'm using a black light where we had a water issue and I see the same brightish purple on the wood in spots.
    – Brad
    Aug 19, 2017 at 19:36

2 Answers 2


What's the humidity level in the room? I'd go get a $12 humidity sensor and see what you got. My understanding that mold can grow >= 60% RH, though there are other factors (e.g. moisture will condense on a cold wall with a lower relative humidity). You may need a dehumidifier if you're too high. Of course that won't kill the mold but will keep it from growing.


It might just be glue, if the door is stained, the stain would highlight the yellow of the glue.


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