The brightness of 2° centrally fixated monochromatic lights was measured by three methods: magnitude estimation, in which the observer made numerical estimates of brightness; delayed matching, in which he adjusted the luminance of an achromatic field until it matched the remembered brightness of the monochromatic field; and conventional heterochromatic photometry. The photometry data resemble the CIE Vλ function, but both the estimation and delayed-matching procedures result in substantially higher sensitivities to short-wavelength stimuli. Part of this excess sensitivity is due to scotopic intrusion and can be eliminated by light adaptation. The remaining sensitivity to short-wavelength stimuli resembles the sensitivity of peripheral cones.
C. R. Cavonius and R. Hilz, "Brightness of isolated colored lights," J. Opt. Soc. Am. 63, 884-888 (1973)