What is a good way to do this?

I'm tring to figure out the best way to view bioluminescent algae for a science fair project. The algae glows when distributed, in this case gently shaken, in its 50ml flask. The issue is it can only be observed at night with minimal or no light. Given that this project will be judged during the day, the algae has been on a schedule so it will glow during the day but still requires darkness. What is a user friendly way of making it viewable to the science fair judges without turning out the lights? My thoughts were to some how make a small box to view the algae or use a curtain somehow. Any ideas?