Time out for a little (very little) physics!
The light given off by hydrogen in the tube or by the sun, or by a fire in a fire place, or by a red hot piece of metal is essentially the same thing as the radio waves that carry your favorite programs to you or the x-rays used to take pictures of your teeth. All are a part of the ELECTROMAGNETIC SPECTRUM.
The visible spectrum is just a small part of this range. Three quantities are needed to completely describe EMR:
- wavelength, l (lambda) (m)
- frequency, n (nu) (Hz or s-1 )
- speed, c (3.0 x 108 m/s)
These three are related by a simple formula: c = ln