How to Detect Mold With a Black Light

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Things You'll Need

  • Relative humidity sensor

  • Black light


You can purchase an ultraviolet lamp (black light) at many party supply stores, music supply stores (in the DJ supply section), and some hardware stores.


If you find signs of mold contamination, contact a mold removal specialist immediately. Left unattended, mold can spread beyond its initial location and endanger your home and health.

Mold is more than simply an inconvenience; it raises serious health concerns. The presence of mold inside the home can contribute to problems such as allergies, asthma attacks, nausea, and other issues. If you suspect your home may be affected, you should immediately try to locate the source. While you can easily spot some mold by its moist, brown, black or gray appearance, some mold may not present itself to the naked eye, particularly if it lingers inside walls. A black light can help you spot this hidden mold.

Step 1

Inspect your home for telltale signs of mold. Observe your walls, tiles, fabrics, books, and other objects in rooms where excess moisture or humidity presents itself. Mold breeds in environments with more than 55 percent relative humidity. You can purchase a portable relative humidity sensor, and carry it into each room to detect current humidity, if you want to gain an accurate sense of your likelihood of mold contamination.

Step 2

Carry your black light into rooms or areas where you suspect possible mold contamination. Shine the light directly over your walls, grout, wooden fixtures, and fabrics, and look for signs of a bright yellow or chartreuse (green-yellow) glow.

Step 3

Verify that the glow indicates mold contamination. Certain cleaning products and inks emit a yellow glow as well. If, for instance, you find the glow on a recently washed fabric or a sheet of paper with highlighter ink on it, you can discount the likelihood of mold contamination. If, however, you find none of these chemicals or products present, and the area appears somewhat damp and possibly accompanied by a musty odor, you likely have mold contamination.


Chris Anzalone

Chris Anzalone has been writing professionally since 2001. He is a former staff writer and associate editor for Opposing Views, a popular news media website that tackles issues of the day from multiple perspectives. Anzalone holds a Bachelor of Arts in English from the University of California at Riverside.