Light and Color

Ancient Theories Earlier views of light believed that something like a streamer went out from the eye and gave us sight.

Newton came up with a theory of light that said it was particle in nature and came to the eye from a source.

A contemporary of Newton’s, Christian Huygen’s, believed that light traveled in waves. In 1905, Einstein published a paper called the Photoelectric Effect, stating that light traveled in massless bundles of electromagnetic energy called photons.

Current view Today it is agreed upon that light has a dual nature, part particle and part wave. This idea is called the “duality of light”.

The speed of light The speed of light was a mystery up until recent times. Olaus Roemer discovered a discrepancy with the time it took for one of the moons of Jupiter to reappear as it orbited.

Albert Michelson used a setup of mirrors and measured the speed of light in He became the first American to receive the Nobel Prize in science.

The speed of light is 300,000,000 m/s in a vacuum and is slightly less through transparent materials. A light year is the distance light travels in one year(9.5 x km. It takes light 8 min to reach us from the sun and 4 years from the nearest star, Alpha centauri.

Light travels as energy waves that come from vibrating electrons in atoms. These waves are called electromagnetic waves and are the same as x-rays and radio waves. The only difference is their frequency.

The electromagnetic spectrum

Light is transferred through matter in much the same way that sound is, by vibrations. A transparent material is one that allows light to travel in through in straight lines ( ex. glass and clear plastic)

An opaque material is one that absorbs light and turns it into heat energy. A translucent material allows light through but cannot be seen through (Ex. frosted glass)

A ray is a thin beam of light. Blocked light rays cause shadows. An umbra is a total shadow and a penumbra is a partial shadow.

Light travels in transverse waves that vibrate in all directions. When a wave vibrates in only one direction, it is said to be polarized.

Polaroid filters Certain filters are capable of polarizing light and are useful in sunglasses since they greatly reduce glare 3-D movies also use this phenomenon. They are filmed and projected with two lenses to give increased depth.

Color The color of an object is the result of the frequencies of light it emits or reflects. A red rose reflects red light. It will absorb all others colors of the spectrum. If placed in green light the rose reflects no light and will be black.

White light A white object will reflect all colors and will be white in white light. White light (such as sunlight) contains all the colors of the visible spectrum. A black object absorbs all the colors of the spectrum. Black is the absence of light.

Light is absorbed when its frequency matches a natural vibration frequency of electrons in the material. This is a form of resonance.

Combining colors Color mixing occurs when light or pigments get combined. Combining colors of light is called color addition. Combining colors of pigment is called color subtraction.

The eyes sees an equal combination of red, green, and blue light as white. Red, green, and blue are the additive primary colors. Magenta, cyan and yellow are the subtractive primary colors.

The sky is blue due to the random scattering of the high frequency blue and violet light by the oxygen and nitrogen molecules in the atmosphere.

Sunrises and sunsets The low frequency yellow, orange and red light gets transmitted. If the sun is at a low angle virtually all the high frequency colors get scattered out and the sun appears deep orange or red.

Bright line spectra Each element has a characteristic line spectra that is like its fingerprint. This is how atoms can be identified without directly examining an object. Ex. Composition of planets and stars