| A | B |
|---|
| Lumen | The luminous flux on a unit surface all points of which are at a unit distance from a point source of one candle. |
| Huygen's Principle | Each point on a wavefront may be regarded as a new source of disturbance. |
| Illuminated | Anobject which is seen because of the light scattered from it is said to be this. |
| Light | Radiant energy which a human observer can see. |
| Sperical Aberration | The failure of parallel ays to meet at a single point after reflection or refraction on a spherical surface. |
| Candle | 1/60 of the luminous intensity of a square centimeter of a black body radiator, maintained at the temp of freezing platinum, 2046 degrees Kelvin. |
| Illumination | The density of luminous flux on a surface. |
| Reflectance | The ratio of the light reflected from a surface to the total light faling on it. |
| Real Image | An image formed by rays of light actually passing through the image point. |
| Virtual Image | Rays of light which appear to have diverged from the image point but do not actually pass through that point. |
| Photometry | The quantitative study of light. |
| Luminous Flux | That part of the total energy radiated per unit time from a luminous source which is capable of producing the sensation of sight. |
| Luminous | An object which gives off light because of the enrgy of its accelerated particles. |
| Luminous Intensity | The 'brightness' of a luminous source expressed in candles. |
| Inverse Square Law | When a physcial quantity varies with the inverse square of the distance. |
