Perth 7th March2013
I don’t watch that much TV but occasionally I do and a few days ago I caught a program called Myth Busters in which they tried to debunk a “Myth” as seen in a movie (I believe the Mummy) where they channel sunlight with mirrors to deep inside a pyramid. They wanted to figure out whether the Hollywood movie’s depiction of the lighting effects, were based on reality. So obviously when they started to talk about lux levels and reflection properties of materials I sat up and focussed a bit more. The object of their program was to find out whether the “myth” is busted, plausible or confirmed.
They actually went about it quite professionally and systematically, by first determining the references from bright daylight to the minimum level of light needed to safely move through an area without knocking over any objects (in the movie scene they come from bright daylight into this dark tomb that is full of treasures; and to find their way they use a set of mirrors to illuminate the interiors). By systematically dimming down the lighting levels they figured out that 0.39 lux was the minimum lighting level needed to safely move around. Considering that full moon is about 0.25 lux, an acceptable outcome. Comparing the movie images with reproduced reference lighting they estimated that the movie brightness would have been 200 lux in the beams…
They ten set out to put the mirrors more or less in the same configuration in an underground area and tested different mirror materials; polished metal and mirrored glass. They figured out quickly that polished metal diffused the light too much and could not reach further then the first few mirrors. The glass mirror however produced a fine reflected beam that reached all the way to the last mirror achieving in excess of 2 lux…so far so good. They also worked out that if someone intercepted the beam with their body (and white shirt!) at the end, light would be nicely scattered in the space! Yes! Lighting levels up to 8 lux, so definitely enough to safely walk around, but definitely not the 200 lux anticipated! So while bringing in sunlight all the way down was found plausible, the part that got busted was that the sun does not stay in the same position so any fixed set up with mirrors would have only lasted minutes….
Light Watch 4-40: Here are some images, first the original movie scenes, then the re-enacting.