Rods are more numerous, and are much more sensitive to light. The light only leaked out a little bit, but when he managed to set it up so that the red flashes coincided with the loud beating of the heart it was really effective, as though the house itself was alive. Even then, you don’t want your light source to be too bright. Find a dark place under a dark sky, and simply watch the stars. Why are red lights used in darkened control rooms and other low-light situations? How did some crime fiction come to be described as “hard-boiled”? Darkroom safelights are typically red or amber. Send questions to Cecil via cecil@straightdope.com. Using this red flashlight can help people get into position safely without creating light pollution that would reduce the number of visible stars. But, if you use a red light your eyes won't adjust to it like that and if you turn it off you should still be able to still quite well in dim light. Rod cells max out in about thirty minutes. Both rods and cones become “blind” to light if they are over exposed. While red lights can help in that respect, things are not quite that simple. The light from one of these flashlights tends to be somewhat brighter than the light from a traditional flashlight, but is not normally a strain to the eyes. Since rods are less sensitive to red light (below 650 nanometers) you can use a red light source to view things without ruining your night vision. One of the advantages of an LED flashlight is that the bulbs tend to last longer than those of halogen flashlights. How did “nuts” and “bananas” come to mean “crazy”? Once that happens, you have a half hour or more to regain dark sensitivity, which can seriously hamper your astronomy experience. While red lights can help in that respect, things are not quite that simple. It's just one of those little things that makes life a bit more comfortable. In movies you see submarine control rooms bathed in red light, maybe because it won't mess up the periscope guy's night vision (or it looks cool), while BMW uses only red light to illuminate the gauges and dashboard displays of its cars. Simply taping a red filter over a flashlight isn’t a great solution. And sometimes I put them into pumpkins, although white or blue lights will work just as well for those. I've heard for years that red light supposedly doesn't affect the ability of the human eye to see in the dark (or a "dark-adapted" eye, to be precise). Although red lights are most commonly used, another solution is to use a cyan-green light. I've heard for years that red light supposedly doesn't affect the ability of the human eye to see in the dark (or a "dark-adapted" eye, to be precise). In near-absolute darkness, both cone and rod cells compensate by pumping out more light-sensitive chemicals. It may still be used during the day for signaling, reading maps, and other tasks. I keep a red light near my bed so that if I wake up in the night it won't blind me when I turn it on. One year I put a red flashlight behind a black cutout of some eyes and put it on a slow blink, which seemed to startle people. When used in conjunction with a rifle scope, this tactical flashlight greatly increases a hunter's chance of success when hunting both small and large game. Cheap filters don’t block other colors very well, so a bright flashlight with a red filter can still ruin your evening.