Table 1. Experimental conditions.

Values in degrees are the diameters of the circular targets or backgrounds. Illuminance ranges are in units of log₁₀ trolands.

Study	Target	Background/ Surround	Illuminance range	Notes
De Lange [14]	2° white.	60° matching surround.	-0.43–4.00	Poor luminance control at lower luminance.
Kelly [15]	50° white, vignetted from 50 to 68°.	None.	-1.22–3.97
Roufs [17]	1° “practically” white.	None.	0.30–4.40
Stockman et al. [13]	4° 610-nm.	9°, 540-nm background.	0.42–5.69	Protanopes. Radiances chosen so that the maximum M-cone contrast is 13%.
Rovamo et al. [18]	1.66°, white.	3.32°, matching white surround.	-0.70–3.40
Swanson et al. [19]	2° red and green LEDs metameric with 600-nm light	None.	-0.05–2.95
von Wiegand et al. [20]	1° falling to zero intensity at 2° with a cosine function, 625-nm.	Matching 18° annular surround, all on an 18° 565-nm background.	0.64–3.64