What Is Light?
Light is energy that moves in tiny particles known as photons.
Light waves are very similar to sound waves, but can move much faster. Sound travels at about 1090 feet per second or 330 meters per second while light travels at 186,000 miles per second or 299792.458 kilometers per second. The speed of light is often written as the letter C. Another difference between light and sound waves is that while sound must have some form of matter in which to travel, such as air or water, light can travel through the vacuum
of space. That is how light from the sun gets to us or how we can see the light from distant stars.
The waves have a wavelength.
That is the distance between the crest (high spot) of one wave and the crest of the next wave.
Each kind of light moves with a different wavelength. Some move in short wavelengths like x-rays.
These waves have a huge amount of energy. UV waves from the sun are another example of this. If we get too much it damages our skin; giving us a sunburn or worse.
moves at a more medium wavelength – that is why we can see it. But even visible light has many different wavelengths within it. More on that later.
Then there are the longer wavelengths. These include radio and television waves and also microwaves. You might even have a microwave oven to cook with in your kitchen.
Longer and shorter wavelengths are not visible to our eyes without special equipment. Only visible light moves in such a way that we can see it.
Every kind of light moves at a certain wavelength. If each wavelength was laid out on a chart, it would create what is called the electromagnetic spectrum.
The shorter waves would be on one end and the longer ones would be on the other. In the middle would be where visible light would end up. That is because it moves at just the right wavelength for our eyes to see it.
Within the visible light of the electromagnetic spectrum are still more wavelengths. Each wavelength is perceived
by our eyes as a different color. The shorter wavelengths of visible light are violet – we might call them purple. Then as the wavelengths get longer and longer, the visible light changes in color to blue, green, yellow, orange, and finally the longest which is red.
Some animals can see waves of light that humans cannot. Those waves would be just outside the edges of human visible light. For example, insects can see ultraviolet waves - waves just past purple on the electromagnetic spectrum. But we are not able to see these. At the same time, there are colors of red that insects are unable to see, but that humans can.
Most light that we use – like sunlight or light from a light bulb – is actually a mixture of all of the visible light wavelengths. It is called white light. When it is mixed, it is difficult for us to separate the colors out. We just see it as useful light. But at certain times the light does get separated out.
The visible spectrum of light is often mixed together in what is called white light.
We do not see each of the colors when they’re mixed together. In order for that to happen, something must separate the wavelengths into their various colors. This can happen in a rainbow.
When light passes through certain materials such as water droplets from a storm or a sprinkler, the light can bend. If it bends just right (and it has to be just right), each of the different wavelengths can be seen. Because the bending has to be just right, sometimes you won’t see the full arch of a rainbow. Some of it may be missing or even appear to hide inside of a cloud.
The colors in a rainbow appear to be red on the top and progress down through orange, yellow, green, blue, indigo,
and violet. Violet is another word for purple. Many scientists argue that there really isn’t indigo in a rainbow. But tradition has created that so that the colors spell out an easily remembered name: ROY G. BIV. Next time you see a rainbow see if you can spot the indigo- a kind of blue purple.
Did You Know?
Rainbows form an arch because of the way the light has to be bent in order to separate out the colors for your eyes to see them. The rainbow you see is just your rainbow. Your friend standing next to you actually sees an entirely different rainbow. Think of it this way: if you were to sit on the sidewalk next to your friend and each of you had a piece of chalk. You took your piece of chalk and reached far out in front of you and drew a line that matched your farthest reach from left to right, it would form a curve – a sort of rainbow. Now your friend repeats this same activity. Even though you were sitting right beside each other, your curved lines didn't sit directly on top of one another. The same is true for the rainbow you see after a storm. From left to right, the bent light is exactly the right distance and bent just the right amount from your eyes for you to see it. Your friend is in a slightly different location – so they see another rainbow.
are another way that light can be bent. Prisms are actually a specially cut piece of glass or other clear material. If placed just right in a stream of white light, they can also separate the light into its various colors. You may have played with one before. Sometimes other things can act as prisms such as the edge of a glass, a CD or a piece of jewelry.
How Light Behaves
Besides being bent by prisms or water droplets, light has the ability to change direction.
Reflected light –
light that hits a surface and bounces off is called reflected light. We see objects because of reflected light. If the surface is slightly rough, some of the light scatters
as it bounces off. If the surface is very smooth the light scatters less and you can see your image.
Refracted light –
as light travels through air it can move rather easily, but if it gets slowed down by traveling through a piece of glass, it is refracted. A great example of this happens when you have a straw in a glass of liquid. The top of the straw appears to be in a different location than the portion of the straw that is in the drink. The glass and the liquid are refracting the light or slowing it down. It makes the image change. This science is used to make lenses
for eyeglasses, microscopes,
and other visual tools.
How We See Color
We don’t need to have a rainbow to see a red hat or a green leaf. The colors don’t need to be separated out by bending the white light. Instead, what is happening is the object itself is responsible for our seeing a color. The white light is separated in a different way. Some of the light is being absorbed
into the object and some of the light is reflecting off. The red hat is absorbing all of the colors of the white light except the red. The red color reflects off of the hat and travels to our eyes. We see red.
The green leaf absorbs all colors except green which reflects off and we see a green leaf.
Every object that we give a color name to is really absorbing all of the other colors and reflecting the color we see back to our eyes. If an object looks white, all of the colors are reflecting off. If an object appears black that means that it is absorbing all of the colors.
How Light is Affected By Matter
Light tends to travel in a straight line. However, when it comes in contact with other matter, it can sometimes be affected by this matter. Take a look at these situations:
air is transparent – it allows light to pass with only a little interference.
There is a slight bending as light comes through our atmosphere;
that is what causes our sky to be blue. But light from the flashlight travels across a room pretty much the way it came out of the flashlight. Car windows are considered to be transparent.
shower doors are sometimes translucent – it allows light to pass through, but it scatters it just enough that images
on the other side can not been seen clearly. Plastic milk jugs are translucent.
a wall is opaque – no light can travel through it. It stops the light altogether. Doors, chairs, concrete, and wood – they are all opaque.
are special forms of light that are used to perform surgery,
show movies, play music, read bar codes, make copies and so much more. But what is a laser? A laser is just one wavelength (one color) of light that has been specially focused
so that it is concentrated
to a pinpoint. If you would like to learn more, click here.
have very little to do with light – they are more involved with our brain. But let’s talk about them anyway. They often appear to be light related. We see things that are not really there or we see things in a way that we know cannot really take place, but it still seems like it does. These are optical illusions. We enjoy them and have a fun time playing with them. But the truth is they are actually about our brain. It is based on what our brain expects things to be or what our years of experience tell our brain that it should be. Sometimes it appears as if stationary objects move, change size, change colors, or straight things curve. Try this one to the right. Are the vertical lines
angled? They are not – check them with a ruler.
The three colors known as the primary colors - red, yellow and blue - are used in televisions to create all of the colors that you see. If you were to mix any two of these colors, you would get the secondary colors - orange, purple, and green. These six colors are known as the basic color wheel. Artists, photographers, and others work with the color wheel to make things look pleasant. When the colors are arranged according to how they mix, patterns can be seen. For example, artists will often try to use opposite colors from the wheel in projects because opposites actually complement each other. Yellow and purple will go well together and even make each other seem brighter. When used this way they are called complementary colors.
Learn more about the color wheel here.
Play with an interactive color wheel here.