The effects of UV light on mold growth

Author(s): Jim Mauch and George Lyle
Growth & Development Experiment
SED 695B; Fall 2005

Research Question:

How is the growth of mold affected by the presence of ultra violet light?

The goggle sanitizing cabinets in science labs are supposed to destroy biological contaminants by exposure to ultra violet radiation. My question was intended to see if these cabinets really work.




Standards addressed:


  1. Stability in an ecosystem is a balance between competing effects. As a basis for understanding this concept:
    1. Students know biodiversity is the sum total of different kinds of organisms and is affected by alterations of habitats.
    2. Students know how to analyze changes in an ecosystem resulting from changes in climate, human activity, introduction of nonnative species, or changes in population size.
    3. Students know how fluctuations in population size in an ecosystem are determined by the relative rates of birth, immigration, emigration, and death.
Independent variable
Dependent variables
Time The development of mold colonies.

Three cabinets are in the same room, exposed to the same temperatures.

A third set of dishes is exposed to light from grow lamp. This control demonstrates whether exposure to any electromagnetic radiation will have the same effect.

Each petri dish is kept at the same level of moisture, with the same amount of sugar, and inoculated with drops of spore suspension in the same five places.

3 dishes in dark

3 dishes under grow lamp

3 dishes under uv lamp


Bread mold
9 petri dishes
filter paper
1% sugar solution
mold spore suspension (distilled water, mold sample, drops of liquid soap)
UV lamp
fluorescent grow lamp
3 cabinets
metric ruler

  • Grow mold colonies on pieces of bread
  • When mold is growing, set up each of 9 petri dishes in this manner;
    • soak a piece of filter paper in 1% sugar solution
    • place the filter paper in the bottom of the petri dish
  • Prepare a solution of distilled water and a few drops of soap in a flask
  • Extract a colony of mold from the moldy bread and place in the flask
  • Swirl vigorously to suspend the spores
  • Place a drop of the suspension in the center, and in the 'north, south east and west' edge of each petri dish
  • Position the UV and grow lights in two cabinets so that they will be several inches above the petri dishes placed under them
  • Place three petri dishes in each of the three cabinets; one with no light, one with UV light, and one with the grow light.
  • Observe the dishes each day. Record the number of colonies and the average size on each dish. Replenish the water as needed each day. (using distilled water)
date Dark   Grow light  UV 
  colonies sizes (mm) colonies sizes (mm) colonies sizes (mm)
10/21 0   0   0 0
10/22 0   0   0 0
10/23 0   0   0 0
10/24 10 2 1 0.5 0 0
10/25 16 4 4 1 1 0
10/26 17 5 4 2 1 3
10/27 17 8 4 2 1 3
10/28 17 12 5 2 1 3
10/29 17 13 5 3 1 3
10/30 18 15 5 2 0 0
10/31 18 15 5 2 0 0




Mold was collected from these colonies and a spore suspension was made
The colonies are not very visible. The black spores are really what are noticeable
The only colony that grew under UV light was on this dish. The yellowish dot is a small amount of the bread residue that was in the spore suspension.
Close up on the only colony growing under UV light. This was at its largest.

References & Links:

Air lights: A company that sells air purifiers using UV light

Research: Lethal effects of UV radiation on fungal spores.