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'), 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', and the luminous-efficiency functions converged to curves that resemble the CIE V (lambda ) or Judd's modification. It seems unnecessary to introduce a new luminous-efficiency function for point sources, which is fortunate for practical purposes.