Electromagnetic energy travels at the speed of light
(approx. 2.9x10^8 m/s or 186,000 miles/sec) in the form of a wave.
distance between two corresponding points on two consecutive waves
range in scale from that of an atomic nucleus (gamma rays) to that of a small planet (radio waves).
lie between 400 and 700nm,with red light at the longer end of the spectrum and violet light at the shorter end.
visible spectrum from 1 to 400nm lies
just above from 750nm to 1mm
index of refraction
is a measure of how much the speed of light is altered as enters a given media relative to the speed of light in air.
n = speed of light in air / speed of light in selected material
Power = 1 / Focal Distance
EX:Power = 1 / Focal Distance
Power = 1 / 0.50 m
Power = 2.00 D
can be used to correct vision for an individual whose eyes are not perfectly aligned as with, for example, a patient with strabismus
specifies the direction if the prism in terms of the base, using base-up, base-down, base-in, and base-out (base-in referring to the direction of the nose and base-out referring to the direction of the temple)
Prism= hcm xD
likened to two prisms base-to-base, as the lens is thicker in the middle and thinner at the edges.
two prisms apex-to-apex, thinner in the middle and thicker at the edges.
prism by decentration
the lens power is sufficient, to induce the prescribed prism, the lens can simply be cut off-center to achieve the required results