When I say white light I mean any light that contains all the visible colors at approximately the same level. So we can get white light from a bulb, or from light that is reflected off of some white surface, such as a white wall or a piece of white paper. Colored light is light that does not have all of the colors in it. Colored light can be from a colored source, such as a red LED or it can be from a surface that absorbs all the other colors. For example a red apple is red because if you let a white light fall on it all the colors except red are absorbed. That is the way the colors of the objects in your room work.
I think we may be having a slight problem with the way you are using the word 'clear'. Clear light doesn't have much meaning to me. I just think of light as light. Clear to me means something like a window which is clear because it doesn't block the passage of light. And light is any light that we can see, it can have any color.
The only transmission medium that is concerned with light is basically space itself. I want to keep this as simple as possible so I won't go into a discussion of the transmission of light.
Back to color. Have you ever had an art class where the teacher explained how colors work? You may recall the primary colors Red, Blue, and Green. In art you make up different colors by combining those three primary colors. White is the combination of all three colors. That is how, for example whatever device you are seeing this on works. It has very small dots of the 3 primary colors. The colors you see depend on how much of each of those colors is turned on. That is how light and color work. Light is just waves in space. Color depends on the wavelength of those waves. Different combinations of those colors are perceived as different colors. So the colors of objects are not modulations of the light but simple reflection and absorption. And darkness is simply the absence of light.
I think you may be being confused by your sons night vision goggles letting him see in the dark. That requires a bit more explanation. I have been talking about visible light. But visible light isn't all there is. Light is electromagnetic radiation. That can be a big subject, but keeping it as simple as possible. I mentioned the wavelength of light. Electromagnetic radiation exists with many wavelengths that we cannot see. If you have a radio then the radio waves that come through the air to your radio are electromagnetic waves with much longer wavelengths than what we can see. If you have ever had an X-ray the X-rays are electromagnetic waves with much shorter wavelengths than what we can see. All around the wavelengths that our eyes can perceive there are others that are invisible to us. You sons night vision goggles can detect some of these wavelengths in what are called the infrared (IR) spectrum. They are also what you feel as heat if you stand in front of a radiant heater. Anything that is warm radiates infrared wavelengths. The warmer it is the more it radiates. The goggles detect these wavelengths and through the magic of modern science presents the pattern of the detected IR on screens in the goggles. That way he can see what is warm around him. So in the visible dark, there is no light, but in the IR there is still 'light' to be detected. It isn't really that he is seeing in the dark. He is just seeing the light that is there, but our eyes can't detect.
Here is a link to the Wikipedia article on
InfraredIf you need more clarification, and you might I'm not a real teacher, don't be afraid to ask.
Bill Gill
