Light Questions form an 8th grader.

[Joshua Buffone]

I was in my room, with my lamp on and a book in my hand. The book was blue. I set down my book, nearer to my lamps light, and saw how the blue of the books front page became somewhat brighter. I then turned off my lamp and was now in a pitch black room. I could not see any color whatsoever from the book anymore. I noticed this and went into the living room, where we have a dimmer-switch lamp. The room was pitch black, like my room. There was no color from the book. I slowly brightened the lamp, and as I did so, so did the colors of the book. At very dim light, the book was a dim, dark blue, and as I brightened the light, the blue would become brighter, and more majestic. Going solely on my observations, I inferred that light was an amplifier of color. Am I correct? Answer my three questions below, please.

 

Is my blue book blue even without the presence of light?

 

Is light really an amplifier of color?

 

What makes an object a certain color?

[Benjwgarner]

Good question, Joshua, and good experiment to test it, quite a bright idea (sorry about the pun, it won't happen again.) Light doesn't just amplify color, color itself is light. When you see an object, light coming from the light source (in this case, the lamp) reflects off the object (the book) and enters your eyeball, where this information is sent to the brain. The white light emitted from the lamp contains all colors. The book has a pigment in it which reflects blue light and absorbs all other wavelengths. Diffferent colors are different wavelengths of light. When the lamp was dim, only a small ammount of blue light was reflecting off the book. When it was off, none was reflected. No object really "is a color", it just reflects a certain color of light. White is combination of all colors of light, while black is the lack of colors. An object that is black under white light absorbs all incoming light wavelengths. In the dark, your book, clothing, walls, and anything else is black, because no light is reflecting from it. It's not just that you can't see what color things are, they don't have a color. They do, however, retain the property of reflecting certain colors of light if a light were present (Obviously, because your book wasn't black when you turned the light back on.) When you brightened the lamp, more light was reflecting off the book and entering your eyeball, thus making the blue color brighter. The book was dimmer further away from the lamp because it was less concentrated. As light travels, it diffuses, or spreads out. Thus less of the light from the lamp hit the book further away than closer to it, because it was covering a smaller portion of the area lit by the lamp. The same thing happens with a hose. If you spray someone up close, they get very wet because they recieve all the water. If they are further away, only a few droplets hit them because the spray spreads out. Also, if you were to light the book only with a pure red light, for example, it would appear black becaue the pigment only reflects blue light. Hope this answers your question.

Edited April 9, 2010 by Benjwgarner
Fixing a typo, and clarification of some ideas.

[Joshua Buffone]

Thank you. I feel like I've failed my teachers, though, for you have used the exact vocabulary and logic that our teachers have taught us, and yet I have asked questions like I didnt know the answer to them. I am grateful that you've re-awakened my knowledge of light.

 

What I wonder about now is color. All colors have an individual wavelength correct? Then why can color be seen differently by different people? Ex: I could take two people in the same lighted room and show them my blue book (which, by the way, is "All Quiet on the Western Front"), yet one of them could have a different color experience that another. If my blue book has only one frequencey in this lighted room, why can this happen? Is it some sort of differentiation in their brains? Is it misinterpretation?

[Cap'n Refsmmat]

Colors can mix together and be perceived differently as well. For example, your computer monitor creates all the colors it displays by mixing together red, green and blue light.

 

However, people experiencing different colors are likely biological differences, like color blindness or differences in their eyes. Or brain, I'm not sure.

[Iggy]

Excellent questions Joshua.

 

I then turned off my lamp and was now in a pitch black room. I could not see any color whatsoever from the book anymore.

 

On the human retina there are two types of light-sensing cells--rods and cones. They detect light and send signals to the brain where an image is interpreted. Rods are more sensitive than cones which means if you are in a dark environment observing something that is scarcely lit then you see it almost entirely with rods. Rods cannot distinguish or perceive color like cones can--they can only distinguish the intensity of light. This means that people see things more and more desaturated of color in a darker and darker environment. In a sufficiently dark environment people see things in monochrome or what you might call black and white.

Edited April 10, 2010 by Iggy
mixed up rods and cones

[Martin]

Thanks Iggy! that's how I would have tried to respond to the question if you had not already replied.

 

This hyperphysics website link you gave is really good!

http://hyperphysics.phy-astr.gsu.edu/Hbase/vision/rodcone.html

 

Retina cells are two kinds: cones and rods. Cone cells do color vision and aren't as sensitive to low levels of light.

 

Rod cells do black-and-white (i.e. gray-level) vision and are more sensitive than cones are at most wavelengths. Except for red, the rod cells are not very sensitive to red for some reason. In any case they don't distinguish colors. When you see with rods your brain is only getting B&W images.

 

So that's why something that is intense blue in good illumination is going to look dull blue---and even gray---in reduced illumination.

 

Color vision is fascinating. That link Iggy gave has some stuff on it. There are a halfdozen short articles, all worth reading.

[Mr Skeptic]

What I wonder about now is color. All colors have an individual wavelength correct?

 

Both correct and incorrect. For every color, there is a wavelength of light. However, normal people detect colors based on the different responses of red, green, and blue cone cells. This means that combinations of different colors of light will be seen as a single color.

 

Then why can color be seen differently by different people? Ex: I could take two people in the same lighted room and show them my blue book (which, by the way, is "All Quiet on the Western Front"), yet one of them could have a different color experience that another. If my blue book has only one frequencey in this lighted room, why can this happen? Is it some sort of differentiation in their brains? Is it misinterpretation?

 

There's a few reasons. Some people are missing one or more of the types of color cone cells, making them partially or completely colorblind. Then the brain interprets things. Having a different language can affect how you interpret colors (some languages have names for various colors while others don't).