BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="elkcub" data-source="post: 3149381" data-attributes="member: 14473">Well, while we're kicking things around I might as well present an alternative to Gijs' statement in post #32, which is presented in radiomentric terms even though brightness perception is to be understood photometrically.  "Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye." (Michael Bass (ed.), Handbook of Optics Volume II.When Gijs says:  it needs to be clarified that the essential factor for perceived brightness is the number of lumens presented to the eye.  This is a color-independent measure determined by computing the dot-product (i.e., a weighted sum) of the transmission spectrum and the momentary spectral sensitivity function.  In the mesopic or scotopic adaptive states of the retina, for example, the brightness associated with any given frequency band, i.e., perceived color, is different from what it would be in the photopic state (daylight).  Moreover, it is also true that certain "colors" don't even have a spectral bad, so the perception of purple, for example, is not uniquely determined by optical transmission characteristics, but rather by the retina's momentary adaptive state in combination with it.  It is a "psychophysical" phenomenon.  If it were easy to put all this into plain English, and come up with generalizations that everyone could readily understand, someone would have figured out how to do it long ago.  Unfortunately, the subject of brightness remains arcane, in large part because it can't be approached without one first being willing to venture into the science of photometry.  In addition, one must recognize that in real life (rather than the laboratory) the retina is constantly moving between adaptive states.  I hope this isn't offense to Gijs, who has made an outstanding effort to summarize a great deal of the complicated vision literature.  Nonetheless, brightness can only be understood photometrically. Ed</blockquote>

Verification