21. Define subjective brightness and brightness adaptation?
Subjective brightness means intensity as preserved by the human visual system.
Brightness adaptation means the human visual system can operate only from
scotopic to glare limit. It cannot operate over the range simultaneously. It accomplishes
this large variation by changes in its overall intensity.
22. Define weber ratio
The ratio of increment of illumination to background of illumination is called as
weber ratio.(ie) ?i/i
If the ratio (?i/i) is small, then small percentage of change in intensity is needed
(ie) good brightness adaptation.
If the ratio (?i/i) is large , then large percentage of change in intensity is needed
(ie) poor brightness adaptation.