MythBusters Episode 169: Let There Be Light
Premier Date: June 22, 2011
A system of mirrors can be used to reflect sunlight into an underground area and illuminate it sufficiently to allow safe passage. (Based on a scene in the film The Mummy.)
PLAUSIBLE (BUT RIDICULOUS)
Adam and Jamie built an obstacle course in the shop and used it to determine the minimum level of light needed to see. To match the circumstances shown in the movie, Adam went from a brightly lit area into total darkness, then to the course; his goal was to reach the other end without knocking over any glasses. He succeeded at a level of 0.39 lux, while the pair estimated that the movie scene had used roughly 200 lux.
Next, they set up six mirrors to bounce light back and forth down the length of the shop, using a spotlight as the source. Polished metal mirrors gave 1.13 lux, but caused the beam to spread out after only a few reflections. When modern glass mirrors were used instead, the light level registered at 0.49 lux and the beam stayed focused longer. Adam and Jamie realized that the light needed to scatter in order to illuminate the room.
At Treasure Island in San Francisco Bay, they set up a hangar area as a full-scale tomb and brought in six glass mirrors and a 7,000-watt spotlight. After adjusting the mirrors, they measured a light level of 2.3 lux and could easily see their way around. Once the sky cleared, they reflected sunlight into the tomb and found a peak of 2.5 lux until the sun’s position shifted, throwing off the mirrors’ alignment. Finally, Jamie stood in the light beam, which scattered in the air when it hit his white shirt and gave 8.6 lux. The need to keep adjusting the mirrors, and the unlikely prospect of finding several of them ready to use after thousands of years underground, led them to declare the myth “plausible but ridiculous”.