>> Your prof was correct. Semantic domains, etymology, and all those >> little tidbits of trivia are interesting- but not useful in the final >> analysis because words gain meaning only from context. >[....] >> To isolate a word and assign it meaning is futile. >[....] > >There is more context to the text than the words proximate to >the text.
When looking at brightness specifications of LEDs, the most common specs available are luminous intensity (usually measured in units of candelas or millicandelas) and viewing angle (measured in degrees). The brightness of 1 candela is roughly around the same brightness as a common candle. A millicandela, or mcd, is 1000 times less bright than a candela, hence the prefix milli-. 1000 millicandelas = 1 candela. Since light is not always evenly dispersed, the viewing angle of a light source is very important.
This quantity is measured in terms of the power emitted per unit solid angle from an isotropic radiator, a theoretical point source that radiates equally in all directions in three-dimensional space. The standard unit of luminous flux is the lumen (lm). Reduced to base units in the International System of Units (SI), 1 lm is equivalent to 1 candela steradian (cd Â· sr). This is the same as 1.46 milliwatt (1.46 x 10 -3 W) of radiant power at a wavelength of 555 nm, which lies in the middle of the visible spectrum. Compare radiant intensity. Also see electromagnetic field, lumen, International System of Units (SI), and Table of Physical Units.