[PO1] Light Spectrum & Color Vision

ELECTROMAGNETIC SPECTRUM

refers to the complete range of known vibrations of radiant energy which extends from the shortest wavelength high frequency gamma waves to the longer wavelength low frequency radio waves.

Speed of light

Transverse Nature

No need for medium

Dual Nature

Energy Transfer

Continuous Spectrum

Frequency and Wavelength Relationship

BASIC PROPERTIES OF ELECTROMAGNETIC WAVES

Speed of light

in a vacuum is now defined as exactly 299,792,458 metres per second or 186,282 miles per second

Transverse Nature

oscillations of the electric and magnetic fields occur perpendicular to the direction of wave propagation

Dual Nature

Electromagnetic waves exhibit both wave-like and particle-like properties, a concept known as wave-particle duality.

(Quantum Mechanics)

Continuous Spectrum

The electromagnetic spectrum is continuous, covering a wide range of frequencies and wavelengths.

Frequency and Wavelength Relationship

The frequency (f) and wavelength (λ) of electromagnetic waves are inversely related. As the frequency increases, the wavelength decreases, and vice versa. This relationship is expressed by the equation c=f⋅λ, where c is the speed of light

f

the frequency of the electromagnetic wave in hertz (Hz). (Symbol)

λ

the wavelength of the electromagnetic wave in meters (m).

Visible Light

makes up just a portion of the entire EM spectrum, from 380 – 700 nanometers.

Our Eyes most often perceive visible light from the Sun as white light, but in reality it is made up of a rainbow of different colors.

Each Color in the spectrum has different wavelengths of light from longer red WL to shorter Blue and Violet WL.

radio waves

with WL that range from 100 meters to less than a cm. Use in communication, AM Radio band, television signals

Microwaves

EM that range form approx. 1ft in length, RADAR

Infrared radiation

has wavelengths from 400 nm to 1,000,000 nm (or 1 mm), longer than those of visible light, discernable to human as heat.

Ultraviolet radiation

has shorter wavelengths than visible light, comprising the 100-400 nm part of the spectrum

Gamma rays

EM radiation that are most energetic with WL of less than about 10 trillionths of a meter, produced during nuclear processes

Dispersion of light

The phenomenon of splitting of a beam of white light into its seven constituent colours when passed through a transparent medium.

Newton showed sunlight contains 7 colors, producing a spectrum on the wall

Isaac Newton (1666)

He discovered the dispersion of light.

He discovered that the light is made up of 7 different colours.

UV-A (315-400 nm)

Retinal photoreceptors are sensitive to UV rays between 350-400 nm.

Absorbed by the crystalline lens (315-380)

UV-B (280-315)

This band of UV rays is blocked by the corneal epithelium.

Responsible for snow blindness from reflected sunlight and corneal burn from arc welding.

Cornea is also susceptible to prolonged (blank) radiation resulting in pinguecula and pterygium.

UV-C (200-280 nm)

This band of UV rays from sunlight is blocked by the ozone layer (O3) of the earth's atmosphere.

absorbed by atmosphere before reaching earth.

Spectroscopy

• Study of absorption and emission of light and radiation by matter, as related to wavelength.

• Expanded to include particle interactions (electrons, protons, ions) as a function of collision energy.

• Crucial for modern physics theories: quantum mechanics, relativity (special/general), quantum electrodynamics

Hue

Color family

Intensity/brightness

Dull or vivid

Chrome/Saturation

Free from any mixture of white; richness or poorness of color

spectrum

strip of colors