How to see things in black and white

You know how when the light is very dim, your eyes see things in no color? Is there a light of some sort that you can put in a room that would make it light enough to see things but dark enough to stay monochromatic? Or are there glasses that make you see monochromatic?

You can light the room in monochromatic light, using filters or monochromatic sources. One excellent choice is low-pressure sodium vapor, which produces an extremely monochromatic, saturated yellow light that completely destroys any ability to distinguish colors. Unfortunately, it's not very practical for lighting the inside of a home or office, but it is widely used for streetlights, warehouses, and other areas where color perception is not important.

Glasses with filtered lenses accomplish the same thing more easily.

What you cannot do is change everything literally to black and white. For that, you need an active viewing system such as a night vision system, but even these usually put color into their displays, so you tend to see things in shades of green or yellow rather than purely in black and white. A video camera set to show black and white can also work.

This night vision thing is not about there being any special kind of light, but simply less light; in the eye, in the retina, to be more exact, there are two types of receptors responsible for the detection of light, rod cells and cone cells. Cone cells are responsible for color vision; there are three different types of cone cell, one for green light, one for red light and one for blue light. The combined signals from these three color channels produce our impression of color. Now, these cone cells only function with a lot of light around, as each takes dozens or hundreds of photons to send a signal to the brain - they don't really work in the dark. This is where the rod cells come in; while they are desensitized when there's a lot of light around, they are almost entirely responsible for night vision: even a single photon can be sufficient to cause the rod cell to fire a signal to the brain, which is of course desired under low-light conditions. As you have only one kind of receptor producing signals, the brain cannot fashion any impression of color, and thus the image we see at night is largely monochromatic.

http://en.wikipedia.org/wiki/Rod_cell
http://en.wikipedia.org/wiki/Scotopic_vi…
http://en.wikipedia.org/wiki/Color_visio…

So, no, there is no such light. But you can of course wear color filter glasses that make you see monochromatic, though that one color would be just that - a color, such as green or red.

a small blue light bulb of about five or ten watts should do the job. You can also try to get a small "bl;ack light" bulb.