Mold is a type of fungus, the spores of which are found in almost every environment, according to Florida Solar Energy Center. Whether mould grows faster in a light or dark environment depends on other environmental factors.
Mold often grows in dark areas which may lead some people to believe the mould requires darkness to grow. Mold actually grows in both light and dark environments, but dark areas most often provide the ideal growing conditions for mould. For this reason, mould usually grows faster in the dark.
Mold grows best in warm, humid environments, according to University of Illinois Extension. When light affects the temperature, it changes the growth of mould. For instance, in a cool area with temperatures below the mid-70s, mould grows faster when lights are left on to warm the surrounding air.
Mold grows well indefinitely in the dark when other environmental conditions favour its development. In warm areas, mould grows faster in the dark, where increased moisture means a higher relative humidity.