LUMINOUS-EFFICIENCY FUNCTIONS FOR POINT SOURCES

Luminous-efficiency functions for small fields were measured with flicker photometry and heterochromatic brightness-matching methods for the same two subjects. For the larger stimuli (22. 9 and 11. 5 prime ), the luminous-efficiency functions differed between the two methods. Those obtained by flicker photometry showed a simple narrow shape, whereas those obtained by heterochromatic brightness matching showed increased sensitivity at short and long wavelengths. The difference, however, decreased as the stimulus was reduced to 2. 3 prime , and the luminous-efficiency functions converged to curves that resemble the CIE V( lambda ) or Judd's modification. It is unecessary to introduce a new luminous-efficiency function for point sources, which is fortunate for practical purposes.