This video provides a demonstration of bioluminescent bacteria glowing in the dark.

When some species of bacteria grow to a certain density, they produce light by bioluminescence. Biologist Bonnie Bassler illustrates this phenomenon with two flasks containing Vibrio harveyi bacteria. When the lights are turned off and the flasks are shaken, the bacteria in the flasks glow for different amounts of time.

This clip is from a 2009 Holiday Lecture Series, Exploring Biodiversity: The Search for New Medicines.