When light falls on a surface three things may happen:
i) A fraction 'r' will be reflected.
ii) A fraction 'a' will be absorbed.
iii) A fraction 't' will be transmitted.
For any surface these fractions must add up to 1.
r + a + t = 1
Magnesium oxide will reflect some 98% of the incident light. Silver is also a very good reflector over a fairly limited range of wavelengths but does tarnish with age. Aluminum although not quite so reflective as silver gives a better reflection over a wider range of wavelengths. The absorption of light as it passes through a material is very important especially in the area of fibre optic communication systems.