A luminous efficiency function,<i>V</i>*(<i>λ</i>), for daylight adaptation

Abstract

We propose a new luminosity function, V*(lambda), that improves upon the original CIE 1924 V(lambda) function and its modification by D. B. Judd (1951) and J. J. Vos (1978), while being consistent with a linear combination of the A. Stockman & L. T. Sharpe (2000) long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cone fundamentals. It is based on experimentally determined 25 Hz, 2 degrees diameter, heterochromatic (minimum) flicker photometric data obtained from 40 observers (35 males, 5 females) of known genotype, 22 with the serine variant L(ser180), 16 with the alanine L(ala180) variant, and 2 with both variants of the L-cone photopigment. The matches, from 425 to 675 nm in 5-nm steps, were made on a 3 log troland xenon white (correlated color temperature of 5586 K but tritanopically metameric with CIE D65 standard daylight for the Stockman and Sharpe L- and M-cone fundamentals in quantal units) adapting field of 16 degrees angular subtense, relative to a 560-nm standard. Both the reference standard and test lights were kept near flicker threshold so that, in the region of the targets, the total retinal illuminance averaged 3.19 log trolands. The advantages of the new function are as follows: it forms a consistent set with the new proposed CIE cone fundamentals (which are the Stockman & Sharpe 2000 cone fundamentals); it is based solely on flicker photometry, which is the standard method for defining luminance; it corresponds to a central 2 degrees viewing field, for which the basic laws of brightness matching are valid for flicker photometry; its composition of the serine/alanine L-cone pigment polymorphism (58:42) closely matches the reported incidence in the normal population (56:44; Stockman & Sharpe, 1999); and it specifies luminance for a reproducible, standard daylight condition. V*(lambda) is defined as 1.55L(lambda) + M(lambda), where L(lambda) and M(lambda) are the Stockman & Sharpe L- & M-cone (quantal) fundamentals. It is extrapolated to wavelengths shorter than 425 nm and longer than 675 nm using the Stockman & Sharpe cone fundamentals.