Introduction to Light, Color, and Shadows

Transcription

1 Introduction to Light, Color, and Shadows What is light made out of? -waves, photons, Electromagnetic waves (don t know this one) How do you get color? - different wavelengths of light. What does it mean for something to have a color, why are the walls blue? - The walls reflect the blue light, so they look blue. If all of the lights are gone, are the walls still blue? Can you have color without light? - Somewhat of a philosophical question, see what they say, I say no. What happens when you add colors together? - Get different colors. Have three lamps set up facing a white screen, one blue, one green, and one red. Turn them on one at a time, and ask them what color they see. Be careful because the blue (at least in our case) tended to be not as bright at the red and green, so by the time I had added all three, we got more of a yellowish light than completely white, but it was close). Also try combinations of colors, so they can see that red and green make yellow, blue and green make cyan, and red and blue make magenta. Next, with them all turned on, go in front of them and make a shadow. You ll be able to see in your shadow that you actually have 4 shadows: a yellow shadow, a magenta one, a cyan one, and a black one. What colors are these? probably say purple, blue/green, and yellow. How many of you have color printers at home? - Almost everyone. - Who knows what colors go into your color printer? o Generally at least one person knows, although many say, red, blue, and yellow (the primary colors they learned when they were younger). o So these colors are the ones that the shadows show. - What happens when you add up all the colors in your printer? o Sometimes no one knew this, so ask, what happens when you run out of the black ink, can you still print black? Most say yes. - How do you print black? o All the colors add to give you the black! Then point out the black shadow behind you. So there are two different kinds of colors primary type colors of light blue, green, and red that add up to give you white, and primary pigments cyan, magenta, and yellow that add up to give black.

2 In addition, combinations of two of each of these colors and pigments add to give you one of the other types: Pigment additions: Yellow and cyan = green Yellow and magenta = red Cyan and magenta = blue Light color additions: Blue and red = magenta Blue and green = cyan Red and green = yellow Therefore, you can draw the following pictures: Here is light color addition:

3 Here is pigment addition: Now that we ve talked about how color is made, and you ve told me that different colors represent different wave lengths of light, which color has the longest wavelength of light, which has the shortest? - blue is short - red is long Can then relate this to energy: E = hc/λ Where h is planck s constant, c is the speed of light, and lambda is the wavelength. So you can see energy and wavelength are inversely proportional: smaller wavelength = larger energy, larger wavelength = smaller energy. Think about fire flame = what color is the hottest part of the flame = blue, so there s the most energy or heat in that part of the flame. Then the top of the flame that has cooled down is yellow/orange not as hot.

4 Shadows We saw that shadows were made from the three colored lights. How are shadows made? - an object blocks part of the light, and leaves behind a dark spot. This is a shadow. In our case, you get the colors because the light sources are coming from different angles, and so when some of the light is blocked out, other colors can still get passed and add together: I couldn t figure out how to get yellow though, but here is what it basically looks like: You can trace the rays in straight lines ray theory of light. Shadows are everywhere, what is an example of the largest shadow that is ever made? - an eclipse either solar or lunar How is an eclipse made? - solar: moon passes between sun and earth, it s the moon s shadow on the earth - lunar: earth passes between moon and sun, it s the earth s shadow on the mooon

5 Here s what a solar eclipse looks like: The darkest part of the shadow, where all of the light is completely blocked is called the umbra The part of the shadow where some light can get to, but some of the light is blocked is called the penumbra. It s not a black, more grayish. So in our color shadows, the part that s black is the umbra, and the part where we get the pigment colors caused by combinations of the light colors are examples of penumbras.