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Air preferentially filters blue light (by scattering), but doesn't change the fundamental spectrum (number, position, and intensity of emission or absorption lines, for instance). … Each "stop" corrects for a halving of the total light flux, so if you're down three stops, you have 1/8 the light level. …

Chemically deposit a thin layer of silver (thin enough to see light through) on two sheets of flat glass. … At around 100+ volts, the tourmaline will begin to emit light that will be visible from both sides of the glass sandwich. …

, mind you, just the kind of bulb you might still have in a closet where you almost never turn on the light so the bulb has lasted twenty years, or in an oven). … If you had a genuinely white light to compare, it would look yellow-orange (like an old bulb alongside a modern "cool white" LED). …

First, when fully dark adapted, a healthy, well-nourished human can see light levels that are astonishingly low. … This is a light level low enough not to fog even fast film in a handling time measured in multiple minutes: photographically, it's total darkness. …

In terms of what was known before, say, the 18th century, there were very limited sources of what we'd normally consider rather dim light, but fire wasn't the absolutely only light source (not counting … Another possibility is electric light. …

Anything that depends on light speed for timing would be profoundly affected. Radar comes to mind instantly -- triple the speed of light, suddenly aircraft 50 km away look like 16-17 km. … I think it's fair to say that a sudden large-factor change in the speed of light (in either direction) would be the end of modern civilization -- we'd be back to 1950s power distribution (except that old …

The simple way would be a conical mirror ring (not spinning) anchored at the spin axis. The ticklish bit is that the axis of your Bishop ring needs to point at the local star, and gyroscopic forces m …

What is often missed in discussion of "red stars" (like M class red dwarves) is that the surface temperature of those stars is similar to that of the tungsten filament in an old-style incandescent light … bulb -- which, though fairly yellow when compared to a truly white light source, is still "white" enough that all colors are readily visible. …

There are a number of naturally occurring minerals that phosphoresce -- zinc sulfide, for instance, can store energy from exposure to light and will then continue to glow for some time, but can also be …