Light and Color

Light basics

• Photons: – tiny wave-like particles of light– carry energy

• Light travels in– Rays: straight-line path of light in a vacuum– Waves: …I’ll discuss soon.

Light vs Sound

• Sound travel in longitudinal waves

• Light travel in transverse waves

More Light vs Sound

• Sound waves are created by vibrations

• Light waves are created by matter– Electrons gain energy– They then jump up an energy level– Then falling back– This falling back releases energy in the

form of photons

Light Waves and Electromagnetic Waves

• These photons are electromagnetic waves (waves created by vibrating charges)

• Light is actually only a very small part of all electromagnetic waves

• All electromagnetic waves are created by vibrating charges

Electromagnetic Spectrum• Includes all photons that are created in order of

increasing frequency

• This spectrum includes:– Radio waves– Microwaves– Infrared– Visible Light– Ultraviolet– X-Rays– Gamma Rays

Electromagnetic Spectrum

Radio Waves

Infrared Visible Light

Gamma Rays

X Rays

Ultra-violetMicrowaves

Light Interactions with Matter

• Electromagnetic waves interact with matter in 3 different ways

• We usually use light to describe these ways

More Interactions

• If all of the light passes through the matter, the matter is called transparent

• If the light can’t pass clearly through the matter, the matter is called translucent

• If the light can’t pass through, the matter is called opaque

Light and Color

• Visible Light has primary and secondary colors

• The 3 primary colors of light are– Red– Green– Blue

• The 3 secondary colors of light are– Yellow– Cyan– Magenta

Pigment and Color

• When we look at different things, they appear in different colors

• These colors are actually the reflection or light bouncing off the objects

Dyes and Pigment

• Dyes and pigment are molecules that absorb some types of light and reflect others

• Dyes are small molecules (like solutions)

• Pigments are large molecules (like suspensions)

Dyes, Pigment, and Color

• Dyes and pigment also have primary and secondary colors

• Primary– Yellow– Cyan– Magenta

• Secondary– Red– Green– Blue

The Light Color Wheel

Adding

• The formation of light is an additive process– Red + Green = Yellow– Red + Blue = Magenta– Blue + Green = Cyan

Subtracting

• Dyes and pigment absorb light

• The absorption of light is a subtractive process– Yellow + Magenta = Red– Yellow + Cyan = Green– Cyan + Magenta = Blue