The MythBusters The MythBusters

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”.

It is possible to safely stop an out-of-control car by pulling in front of it with another car and slowing down.


After taking lessons in stunt driving, Grant, Kari, and Tory tested a scenario in which the runaway car would be coasting without the driver’s foot on the accelerator. As Kari drove without using either the steering wheel or the brake/gas pedals, Grant pulled in front and slowed down until he made contact with her bumper. He was able to stop her from a starting speed of 35 mph and again from 55 mph (56 and 89 km/h). They then tested the possibility of a stuck accelerator and no steering. Kari drove at 75 mph (121 km/h) with her foot on the gas pedal; Tory stopped her with some difficulty, just short of hitting a fence. They declared the myth confirmed at this point.

Next, Grant and Tory tried to sandwich Kari’s car from either side and managed to stop her, though they began to spin out somewhat. The two men then built separate car-stoppers: Grant made side paddles to attach to the two rescue cars’ front bumpers (to block in the runaway car), while Tory made a hood-mounted spear to hook the rescue and runaway cars together so the rescuer can slow them both down. Both rigs were successful.