What does “Candela”, “Lumen”, etc. mean?
The formal definition can be found in many handbooks, so here are informal and, hopefully more useful, definitions: Luminous intensity (or candlepower) is the light density within a very small solid angle, in a specified direction. In other words, this is the total number of lumens from a surface emitted in a given direction. The unit of measure is candela. In modern standards, the candela is the basic of all measurements of light and all other units are derived from it. Candlepower measurements are often taken at various angles around the source and the results plotted to give a candlepower distribution curve. Such a curve shows luminous intensity (how “bright” the source seems) in any direction. Luminous flux is the time rate of flow of light. The unit of measure is the Lumen. One lumen may be defined as the light flux emitted in one unit solid angle by a one-candela uniform-point source. The lumen differs from the candela in that it is a measure of light flux irrespective of directi
