Armored Medical Research Laboratory Fort Knox, Kentucky PROJECT NO. 7 - NIGHT VISION FROM TANKS Report On Sub-Project No. 7-2, Determination of Intensity, Distribution and Type of Illumination in Tanks Least Disturbing to Dark Adaptation 7-3. Investigation of Methods of Improving Night Vision in Tank Crews by the Use of Eye Appliances INTERIOR LIGHTING OF ML TANKS Project No, 7-2, 7-3 February 25, 1943 ARMORED FORCE MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky Project Noo 7-2, 7-3 File No. 741 February 25, 1943 INTERIOR LIGHTING OF M4 TANKS 1. PROJECT: No. 7, Night Vision from Tanks, Sub-project No. 7-2, Determination of Intensity, Distribution and Type of Illumination in Tanks Least Disturbing to Dark Adaptation. Sub-project No. 7-3, Investigation of Methods of Improving Night Vision in Tank Crews by the Use of l$ye Appliances. a, Authority: Letter Commanding General, Headauarters Armored Force, Fort Knox, Kentucky, File 400.112/6 GNOHD, dated September 21, 1942. b. Purpose; To adapt controlled white and red lighting, for day and night use, to the M4 tank. 2. DISCUSSION: The advantages of red light as a means of preserving dark adaptation for night tank operations have been discussed in a previous report under project 7-2, The illumination required for daylight operation (10 foot candles or less) in closed tanks is considerably in excess of that necessary for night operations (l foot candle and less) and rad light offers no advantages under these conditions. Furthermore, the electrical energy required for producing red light of a given brightness is much more than that required for white light of equal brightness. A dual lighting system is there- fore needed to provide white light during the day and red light of lower in- tensity at night. This report deals with the problems of fixture design, location of lights, light distribution, intensity and the controls necessary for both types of illumination. 3. CONCLUSIONS; a. Adequate red light illumination for night use is provided by one 6-candle power bulb per fixture coated with a suitable red filter when mounted in the present fixture. b. White light of the required intensity for normal daylight use is provided by one 6-candle power bulb in each fixture,. £0 After exposure to extreme glare (reflection from snow or white sand, for example, on a bright day), illumination of a higher order may be required for difficult tasks. This will necessitate the use of auxiliary lights. do Three dual lighting fixtures are required in the turret, two in the bow and one in the starboard sponson. e. The present light fixture can be modified to permit the installation of both the red and white lights. f. Proper control of brightness for both lights can be obtained with rheostats. 4. RECOMMENDATIONS: a. That the dual lighting and controls described in the appendix be installed in M4 tanks, —three fixtures in the turret, two in the bow and one in the starboard sponson. b. That instructions regarding the proper use of red light for preserving dark adaptation be given to all tank crew members and that night training with the lights be made a part of the advanced training program. c. That the following additional aids to night vision be in- corporated in the >54 tank: (1) Lettering that must be read at low light intensities should be block type, white on black letter at least one inch in height, line width 1/4 inch. (2) All knobs, controls, etc. to be paint- ed white. (3) Instrument panels be redesigned and relocated for better day and night use. (4) Maps for night use to be printed boldly black on white or tonal keyed. Maps with red printing are unsuited for use with red light unless tonal keyed. (See Appendix III) d. That one-half of the regular complement of flashlights be fitted with red filter material. e. That all light fixtures be installed "spring-loaded” to pro- tect against failure when the tank is hit. f. That the reflectors of fixtures be carefully painted with a white, high red-reflecting paint such titanium oxide paint. £, That all switches be capable of withstanding severe vibration. h„ That the trouble-light connections be retained adjacent to commander's light and on the ihstrument panel. tf i. That auxiliary lighting for map and instrument panel reading after exposure to glare of the order 10,000 foot candles (sun on desert or snow) be provided by 32-candle power bulbs to be used in the emergency (trouble) light. Submitted by: Captain Lester B. Roberts, Sn-G APPROVED WILLARD MACHLE, Lieutenant Colonel, Medical Corps, Commanding 0 6 Incls. Appendices I, II, III Figures 1, la, 2 3 APPENDIX I Procedure: Lights were tested in the laboratory and in a tank* Measurements were made of brightness and the amount of illumination supplied by individual fixtures and combinations of fixtures. Tasks within the tank were carried out and the lighting adjusted to provide adequate illumination after exposure to outside light. APPENDIX II For this study, red filter material (designated as 8 AP and meeting specifications for dark adaptation goggle lenses) was used over the white light as the red light source. It was found subsequently, however, that the bulbs can be successfully coated with this material, which makes the use of the filter unnecessary and allows both the red and white light bulbs to be mounted in the same fixture. Light transmission tests on bulbs coated with the material are being carried out. Fig. A shows a suggested schematic wiring diagram for the dual lighting system. Any variations can be made so long as the principle is retained. A 3-position switch (red, off and white) is provided on each fixture. Two master rheostats, one for the commander and one for the driver, control the brightness of both the red and white lights in the turret and bow respectively, A red-white switch on the rheostat control board makes it possible to control the light to be used. Red light is always available (except when master battery switch is turned off) but the white lights can be turned on in the turret only when the commander's rheostat switch is on white and in the bow when the driver's rheostat switch is on white. This limits the control of the white light cind the brightness of either red or white light to these two men and safeguards against white light being used when it would interfere with dark adaptation or reveal the position of the tank. Fixture locations are indicated in Fig, B. The illumination at a distance of one foot from the red light is about 1.2 foot candles; the white light at the same distance provides about 10 foot candles. An illumination of 10 foot candles with white light is sufficient to read detailed maps after exposure to glare of approximately 6000 foot candles (strong sunlight on roads). Extreme brightness of sun on snow is aoproximately 10,000 foot candles. The illumination necessary for detailed map reading after exposure to this intense glare would require extremely high candle power lights in larger fixtures and excessive power consumption. This, however, is an unusual condition which can be met by the use of the trouble light. It is recommended therefore that 32 candle power bulbs be carried for use in the trouble light for operations in the desert or on snow. Bright light (red or white) is supplied for map reading, machine gun clearing, and gun adjustments (elevation wheel or 75 mm gun). The 1 corresponding light sources have been located so as to supply an adequate flood of light throughout the tank with the exception of a few seldom used places where lighting with fixtures is impractical. The use of flashlights in these locations can be continued. APPENDIX III If production limitations prevent the immediate procurement of tonal keyed maps, conventional maps may be used if the red lines are drawn over vdth ink or black crayon. Maps for night use should be procured as soon as possible. Production of maps for night use is under development by the krmy Map Service. THIS LIGHT TO BE REMOVED -"'"'TL — LIGHT TO BE MOUNTED ON INNER SIDE TOP SPONSON LIGHT TO BE MOUNTED BETWEEN TWO INTERPHONE BOXES. MOUNT AND LIGHT TO BE HIDDEN BE- TWEEN PHONE BOXES AND LIGHT TO BE AT A 50°AN6LE. MOUNT TO CONTAIN RHEOSTAT LIGHT TO BE MOUNTED LEVEL WITH FLOOR LINE ON TURRET ROOF \ LIGHT TO BE MOUNTED ’ON TURRET ROOF-FLUSH THIS LIGHT TO REMAIN LIGHT NUMBERS 1 TANK COMMANDER'S LIGHT 2 GUNNER'S LIGHT 3 LOADERS LIGHT 4 ASS’ T DRIVER'S LIGHT 5 RT. SPONSOR LIGHT 6 DRIVER'S LIGHT NOTE LIGHTS NO’S 3 AND 6 NOT SHOWN IN THIS VIEW LOCATIONS FOR DUEL RED AND WHITE LIGHTS FOR M4 TANK FIG. I turret roof LIGHT TO BE MOUNTED WITH FLOOR LINE TURRET ROOF MOUNTING DETAIL RADIO RADIO TURRET WALL PANEL FACE TO BE RtCESStO TO CLEAR PANEL DIAL AND — SWITCH rheostat SWITCH -t. (TWO WAY) COMMANDER’S CONTROL PANEL DETAIL PHONE BOXES TO BE TURNED THRU 90° OR 180° TANK HULL TANK HULL' LIGHT MOUNTING BOX - AND PANEL SHOWING RHEOSTAT CONTROL PHONE BOX PHONE BOX PHONE BOX COMPASS COMPASS DRIVERS LIGHT MOUNTING AND CONTROL PANEL BOX DETAIL FIG. IA ?T. SPONSON LIGHT MO. 9 DRIVER'S LIOHT NO. 2 TURRET LIGHT NO, 2 TURRET LIGHT NO. 3 BOTH WIRES CARRIED IN' yf CONDUIT TROUBLE LIGHT TURRET LIGHT NO. I 0 R - 6 CP BULB COATED WITH W RED FILTER MATERIAL BAP TRANSMISSION MEETING NAVY SPECS O.A. GOGGLE LENS MATERIAL DRIVER'S LIGHT NO. I © W « 6 CP BULB trouble LIGHT COLLECTOR RJN6S SWITCH SCHEMATIC WIRING DIAGRAM FOR DUAL RED AND WHITE LIGHTS FOR M 4 TANKS FIG. 2