The Visible Light Spectrum

 

Home

The Visible Light Spectrum

Molecular Fingerprints

Applications

Links

Bibliography

 

 

 

 

 

 

 

Wavelength of Colors:

 What is Light?

Important Equations/Constants/Variables:
Light can be described as both an oscillating electro-magnetic wave or as little bundles of energy called 'photons'. According to ask.com, a photon is "the quantum of electromagnetic energy, regarded as a discrete particle having zero mass, no electric charge, and an indefinitely long lifetime.6" When a photon of light hits an object, that object's molecule's have ground state electrons that become excited and move to a higher energy level. When the excited electron decays from the higher energy orbit to a lower energy level (i.e. back down to its ground state) light is given off by the molecule in the form of a photon of some wavelength. By setting equations I and II equal to each other  and rearrange the variables we get equation III:

E = (c*h)/λ     Equation III

Since both c and h are fundamental constants we can see that there is a direct correlation between the change in energy (E) and the wavelength (λ). Thus, by measuring the observed wavelengths, we are able to calculate the the transition energy for different molecules. The observed wavelengths themselves are the colors that we see. The visible light spectrum ranges between 400 and 700 nm (nanometers) and are, as equation III states, inversely proportional to the energy associated with the electron level transitions.

For an application of equation III and the relationship between the transition energies and wavelength click on the Molecular Fingerprints link.

Constants:

 c = 3*108 m/s         Speed of Light

 h = 6.636*10-34 J*s   Plank's Constant

Variables:

 λ = wavelength (in meters)

 f = frequency (in hertz or s-1)

 E = energy transfer (in J)

Equations:

 f = c/λ                Equation I

 f = E/h                Equation II

 
Youtube.com provides an excellent movie clip about visible light below:
  Color:

Approximate Wavelength:

    
Ultraviolet

Violet:

Indigo:

Blue:

Green:

Yellow:

Orange:

Red:

≈ 365 nm

≈ 405 nm

≈ 445 nm

≈ 436 nm

≈ 546 nm

≈ 578 nm

≈ 590 nm

≈ 650 nm