In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Coriolis wrote: you are essentially correct mcd is millicandela. Here is an excerpt from [url=http://www.electro-optical.com/whitepapers/candela.htm]http://www.electro-optical.com/whitepapers/candela.htm[/url] [b]Definition: [/b]The candela is the [url=http://www.electro-optical.com/whitepapers/candela.htm#Illuminance Units & Conversions][u]luminous intensity[/u][/url], in a given direction, of a source that emits monochromatic radiation of frequency 540 × 10[sup]12 [/sup]hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. The frequency chosen is that to which the eye is most sensitive. This frequency is normally referred to as the corresponding wavelength: 555 nanometer. The wavelength varies with the medium through which the light passes, so, in the interest of precision, our relatively familiar wavelength description of light is not used in the standard. The strange choice of the number 683 is to make the value identical to that obtained with the previous version of the unit: the emission from 1 square centimeter of glowing, solidifying platinum. The steradian is the cone of light spreading out from the source which would illuminate one square meter of the inner surface of a sphere of 1 m radius around the source. The light intensity coming towards the observer is assumed to be reaching all angles within the enclosing steradian at the same intensity. It doesn't have to in practice: one can perfectly well measure the luminous intensity from a lighthouse beam, knowing that it actually only covers less than a hundredth of a steradian. One measures the light received by a small sensor of known area and multiplies this to give the corresponding value for one steradian. ---------- End of Message ---------- You can view the post on-line at: http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=89554#m89648 Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2005 (http://www.dotNetBB.com)