IT IS GENERALLY accepted that testing with pseudoisochromatic plates should take into consideration the following requirements: (1) neutral illumination; (2) sufficient illumination; (3) a determined angle of the incident light; (4) a 90-degree viewing angle; (5) a fixed distance of the plates; (6) a limited exposure time for each single plate; (7) showing of all plates in their entirety; (8) variation from time to time in order of presentation of the plates.
When the testing arrangements now in use are analyzed briefly with regard to these requirements, the following statements may be made:
In the instructions for testing with pseudoisochromatic plates, illumination by natural daylight from the north sky or artificial daylight is required, since it is known that light obtained from ordinary electric bulbs allows more persons with color-defective vision to pass the plates than a "neutral illumination" (Kissin and Eidelmann1; Farnsworth and Reed2; Hardy, Rand, and
SCHMIDT I, FLECK H. ROTATOR AND ILLUMINATOR FOR PSEUDOISOCHROMATIC PLATES. AMA Arch Ophthalmol. 1952;48(1):75-82. doi:10.1001/archopht.1952.00920010078011