Light and Color Remember the speed of light

Light and Color • Remember the speed of light … 3 x 108 m/s • This is the speed for ALL wavelengths of light and electromagnetic energy. • Red is NOT slower than blue – it merely has less energy and a longer wavelength. • Infrared has less energy than red…ultraviolet has more energy than violet.

Light and Color • In order of least energy to most, longest wavelength to shortest, here are some common forms of electromagnetic energy. Radio Microwave Infrared Visible Ultraviolet X-Rays Gamma

Light and Color • The Visible Light Spectrum – There are 6 main divisions of light ROYGBV • The I…. Newton wanted nature to be harmonic, meaning a color for each note in a musical octave, thus indigo. Indigo is just a shade of blue, so nope. • http: //m. youtube. com/watch? v=9 ud. Yi 7 exojk&feature=youtu. be

Light and Color • Our Sun is a black body - object that produces light due to heat; also absorbs EM Radiation • What is its color? • WHITE! If it were yellow, then when you wore a white t-shirt, what color should your shirt look?

Color and Light • Additive colors are when we see light projected at us, like a TV, using only red, green and blue light to make all of the lights you see on a TV or computer monitor.

Color and Light • Subtractive colors are when we see a reflection of light or light filtered out – MOST of what we see is a reflection. Pigments and dyes use subtractive colors as do color printers. These colors are cyan, magenta and yellow.

Color and Light • Light is made by an atom absorbing energy and then releasing it. • How the atom gains energy varies – electricity, vibrations, chemical reactions, light itself, sound, etc. • If the right amount of energy is received and absorbed by the atom, it causes the electrons to become excited and jump to a higher energy level. • Once excited, an ‘empty’ spot is left in the lower energy level and an electron in the higher level must fall back down to the ground state. When that happens the energy it had while it was in the higher state is released as radiation, regardless of what kind of energy it was when it was absorbed.

Color and Light • The amount of energy absorbed determines how far the electron is pushed up, and therefore how far down there is to fall back to ground state. • The ‘fall’ does not have to be accomplished all at one jump, but may be done in transitional falls, each with a different wavelength.

Color and Light • When light hits an object, it can be reflected, pass through it, or be absorbed. • Opacity is the extent to which radiation is blocked by a material through which it is passing. • If it has a very low opacity, like clear glass, it is said to be transparent.

Color and Light • Earth’s atmosphere has very low opacity to some wavelengths, such as radio waves, visible and small parts of the infrared and ultraviolet spectrums. • Earth's atmosphere is opaque to the rest of the majority of the electromagnetic spectrum and those wavelengths can only be studied from orbiting satellites or sometimes high altitude planes.

Color and Light • Sticking with visible light for the moment…. • Materials that are opaque absorb or reflect most of the visible light that strike them. • The things you see, are seen because of the light that is reflected…and the color is made up of the colors that are reflected. All other colors are absorbed. • Ex: A green shirt looks green because it is absorbing all other colors and only green is being reflected back at you

Color and Light • Radiation that is absorbed often causes the temperature of the object to increase. • What colors are cooler to wear in the summer? • What color car interior heats up faster?

Heat Absorption • When you “feel” heat, you are feeling infrared radiation. • You cannot see infrared, but it is adjacent to red on the electromagnetic spectrum, and materials that reflect red best will also reflect infrared, and materials that absorb red best will also absorb red best.

Heat Absorption Lab • Determine which you think will absorb the infrared from the sun and begin to burn fastest and which will take the longest. • Heat Absorption Lab now……

Heat Absorption Lab • Did you get the results you expected? • If not, the difference often comes down to intensity…. Intensity is the amount, or strength of radiation at any one point in space. • Ex: magenta and purple are both combinations of red and blue, but have varying intensities of each color

Why is the sky blue? • Raleigh Scattering • https: //www. youtube. com/watch? v=VGMnztlt Vh 0 • Atmosphere is made up almost entirely of nitrogen molecules and oxygen molecules (both about the same size) • Sir Raleigh determine that the size of the particle determines the wavelength of radiation that it will scatter the most • Smaller particles scatter shorter wavelengths; longer wavelengths don’t even notice them • For Earth, blue wavelengths are scattered the most…. Some of the other radiation as well, but HUGELY in favor of blue.

• This photo sequence taken in Veszprem, Hungary

Filters • Filters selectively transmit light – color filters transmit certain colors but absorb all others. • • Ex: Look at a red object through a blue filter – the filter only allows blue to reach your eyes, and since the object is red, no blue is coming to you so the object will appear black. Polarized light is light with a magnetic field that vibrates in only one direction. • When light is reflected from surfaces, some of its light is polarized and can be filtered out by using polarizing filters.