Light Waves Day 1

Properties of light Light travels fast over long distances and carries energy and information. Light travels in straight lines, but can be bent by lenses or reflected by mirrors heat and warmth. Light has color and can be bright or dim.

The electromagnetic spectrum Light, like sound and heat, is a form of energy. The visible light we see is part of the electromagnetic spectrum.

Properties of light You see book pages because light in the room reflects from the page to your eyes. Your eyes and brain use the information carried by the light to make a mental picture.

Light is produced by atoms Most light is produced by atoms. When you put some energy into the atom, it excites the atom’s electrons. Light is produced when the electron releases this energy.

Incandescent light Making light with heat is called incandescence. Atoms in the filament convert electrical energy to heat and then to light. Incandescent bulbs are inefficient, but their waste heat can be useful.

Fluorescent light To make light, fluorescent bulbs use high-voltage electricity to energize atoms of gas in the bulb. These atoms release the electrical energy directly as light (not heat), in a process called fluorescence.

Color and energy When all the colors of the rainbow are combined, we see light without any color. We call the combination of all colors white light.

Color and energy Compare the hot, blue flame from a gas stove to the orange flame of a match. The light from a gas flame is blue (high energy) and the light from a match is red-orange (low energy).

Photons and light Light energy comes in tiny bundles called photons. You can think of a photon as a wave with a very short wavelength. Each photon carries the frequency of the light corresponding to its energy.

The speed of light The speed at which light travels through air is about 300 million meters per second. The speed of light is so important in physics that it is given its own symbol, a lower case “c”.

Wavelength and Frequency of Light Because the wavelength of light is so small, scientists measure it in nanometers. One nanometer (nm) is one billionth of a meter (0.000000001 m).

Energy and light Like other waves, the frequency of light is proportional to its energy. Red light has lower energy than blue light and also has a lower frequency.

What kind of wave is light? A sound wave is a oscillation of air. A water wave is an oscillation of the surface of water. An oscillation of electricity or magnetism creates electromagnetic waves.

Electromagnetic waves If you could shake the magnet up and down 450 trillion times per second, you would make waves of red light with a frequency of about 450 THz.

Electromagnetic spectrum The entire range of electromagnetic waves, including all possible frequencies, is called the electromagnetic spectrum. This spectrum includes visible light and invisible waves: radio wave microwaves infrared light ultraviolet light X-rays gamma rays

The human eye The eye is the sensory organ used for vision. The retina contains light-sensitive cells called photoreceptors. Photoreceptors convert light into nerve impulses that travel through the optic nerve to the visual cortex of the brain.

Photoreceptors The human eye has two types of photoreceptors— cones and rods. Cones respond to color and rods respond to the intensity of light. Rod cells “see” black, white, and shades of gray.

How we see color Our eyes work according to an additive color process — 3 photoreceptors (red, green, and blue) in the eye operate together so that we see millions of different colors.

Making an RGB color image A television makes different colors by lighting red, green, and blue pixels in different proportions. Color images in TVs and computers are based on the RGB color model.

Making an RGB color image Like the rods and cones in your retina, a video camcorder has tiny light sensors on a small chip called a CCD. There are three sensors for each pixel of the recorded image: red, green, and blue.

How objects appear to be different colors Your eye creates a sense of color by responding to red, green, and blue light. You don’t see objects in their own light, you see them in reflected light!

Subtractive color process A blue shirt looks blue because it reflects blue light into your eyes. Chemicals known as pigments in the dyes and paints absorb some colors and reflect other colors.

The CMYK color process The subtractive color process is often called CMYK for the four pigments it uses. CMYK stands for cyan, magenta, yellow, and black.