referring now to fig1 there is shown a plan view of the present invention as it would appear in its patient - ready state . the viewing apparatus , generally designated 11 , consists of an opaque background screen 7 preferably dark in color and having a low light reflectance . appearing on the face of background screen 7 are a plurality of transparent disks . in the preferred embodiment , four transparent disks 5a , b , c and d are used . the disks are arranged both in number and pattern to be as user friendly as possible . by using a pattern of four disks , as shown in fig1 the patient can identify the disk which appears different in color as top , bottom , left or right . in addition , by using four color disks as opposed to two or three , the probability of a patient guessing the appropriate disk is reduced ; this becomes particularly important when working with small children in that they : ( 1 ) have an inability to identify letters or numerals and ( 2 ) will often guess in the hope of providing the tester with an appropriate answer . the cover 13 generally conceals the electronics and light sources for providing the red - green , blue - yellow , and blue - green light mixtures shown to the patient through disks 5a , b , c and d . viewing apparatus 11 in the preferred embodiment is mounted on a conventional platform 15 such that the viewing apparatus can be tilted on axis 14 to provide the best viewing angle to the patient . in operation , a patient is seated in front of the viewing apparatus such that he can readily observe the four colored disks 5a , b , c and d . the tester selects a disk ( top , bottom , left or right ) to display a different combination of colors than the three remaining disks and then asks the patient to identify the disk that is different in color and / or intensity . to control the color intensity of the transparent disks 5a , b , c and d , there is a separate key pad generally designated 1 . in the preferred embodiment , key pad 1 is connected to viewing apparatus 11 via conventional cable 9 . however , the key pad could be mounted directly on platform 15 or cover 13 . it should be emphasized that the circuitry in both the key pad 1 and the viewing apparatus 11 are conventionally made from parts which are readily available . the tester , during operation , uses one of four keys 3 ( top , bottom , left , right ) located on the key pad 1 to identify a particular disk 5a , b , c or d , which he wishes to have identified as a different color and / or intensity from the other three disks . for example , a tester , while evaluating a red - green or blue - yellow test , may select to have the bottom disk 5c appear different in color and / or intensity to a normal patient . accordingly , he would select disk 5c from the key pad 1 and would subsequently use a second series of keys 3 to select the color and / or intensity of the red - green or blue - yellow mixtures he wishes to present to the patient . presumably , the test will be performed in a dimly lit room whereby the color disks 5a , b , c and d , can readily be seen and not interfered with by conventional lighting sources , or alternatively a viewing shield may be utilized , such that the subject places his / her head against a gasket to exclude external light . the shield is of the length to place the subject &# 39 ; s eyes at the correct viewing distance from the disks 5a , b , c , and d . referring now to fig2 there is shown a side view partially in cross section of viewing apparatus 11 . shown are three of the four spheres 15a , b and c used to mix the colors presented to the patient through patient viewing ports 5 ( fig3 ). the key pad 1 , as mentioned above , is connected to the viewing apparatus 11 via cable 9 . conventional power control unit 10 is connected to a voltage source via cable 8 and provides the necessary control circuitry to interface with key pad 1 whereby the tester can select which disk 5a , b , c , or d is to be the test disk and adjust the color and intensity accordingly . as shown in fig3 each of the spheres 15a , b , c and d , comprises a plurality of small apertures 16 and a viewing port 5 . a particular color combination , whether red - green , blue - yellow or blue - green , can be created by mixing the light from the red , green , blue , white and yellow lamps inserted into the sphere . it is not necessary that six different lamps be used in that some light sources combine different color lamps into a single bulb ; again , it should be emphasized that such light sources are conventional and readily available . alternatively , depending on the particular use of the color vision testing apparatus , it may only be necessary to have one or two lamp apertures wherein , for example , a single unit is used to test red - green , blue - green , or blue - yellow . in the preferred embodiment , it is considered important to use a sphere as opposed to alternate shape configurations . the use of other shapes is conceivable , for example a square ; however , such shapes could increase the probability of light becoming trapped in corners or cavities thereby interfering with the intensity and thus the color observed by the patient . in addition , improperly shaped mixing cavities can create hot spots which might enable an abnormal patient to identify the different colored light disk . as shown in fig5 lamps 27a , b , c , d , e and f , are inserted through lamp apertures 16 . these lamps can be red , green , blue , white and / or yellow lamps . each sphere should be capable of mixing colors to test red - green and / or blue - yellow color deficiencies . further , it is important that the lamps 27a , b , c , d , e and f , be out of the field of vision as seen through transparent disks 5a , b , c and d . if the lamps are within the field of view , hot spots can again be created thereby cuing the patient as to the different colored disk . alternatively , as can be seen in fig4 lamp access apertures should be configured such that the highest intensity portions of the lamps 27a , b , c , d , and e are directed away from transparent disks 5a , b , c and d . this is best accomplished by placing the lamp apertures on the same hemisphere as viewing port 5 . in a preferred embodiment of the invention , the spheres 15a , b , c and d are created by using a clamshell plate configuration wherein each plate contains 1 / 2 of the sphere 15a , b , c and d ; this is shown in fig4 . when the two plates 21 , 23 are combined they complete four spheres . this is beneficial in that a divided sphere is easier to work with when installing the individual light sources 27a , b , c , d , e and f . as shown in fig2 plates 21 and 23 are secured to opaque background screen using dowels 24 and screws 25 . fig6 shows a second embodiment of the present invention wherein the spheres 15a , b and c are located at distance x away from opaque background screen 7 . this embodiment enhances light mixing characteristics and therefore reduces hot spots as compared to the embodiment of fig2 . the light mixing spheres 15a , b , c and d as shown in fig2 are very close to background screen 7 which in turn places lamps 27a , b , c , d , e and f close to background screen 7 as well . by placing the sphere a distance x from background screen 7 , lamps 27a , b , c , d , e and f are also moved away from background screen 7 , thereby reducing the probability that the patient will notice hot spots created by lamps 27a , b , c , d , e and f in close proximity to the patient . it should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art .
an opaque plate is positioned in front of a patient undergoing color vision testing . a number of openings are formed in the plate . behind each disk is a hollow sphere having colored light sources mounted therein . by selectively energizing the colored light sources in a sphere , a mixture of light is presented at the corresponding transparent disk at a selected intensity . a tester can select one or more spheres to be internally illuminated by color light sources so that the patient is presented with a pattern of selectable color mixtures which checks his color vision .