[Luminescent Materials] [From the U.S. Government Publishing Office, www.gpo.gov] OCD 20 November 1 War Department Specification LUMINESCENT MATERIALS U. S. OFFICE OF CIVILIAN DEFENSE Washington D,C, FOREWORD The standards specified herein may be imposed by military authority during specified periods and in specified areas. Independent of such action these standards afford guides to civilian authorities as to measures that can be taken by them to conform their conduct with what may eventually be prescribed. Due to the scarcity of certain critical materials which will be involved in the manufacture of the equipment called for in these specifications, it is probable that only the most exposed communities in the continental United States will be able to procure the equipment. For this reason these specifications are being given only a limited distribution at this time. ' TABLE OF CONTENTS Paragraph Subject Page 1. Scope_______________________________ 1 2. Definitions____________i____________ 1 a. Luminescent materials_____________ 1 b. Radioactive materials______________ 1 c. Phosphorescent materials___________ 1 d. Fluorescent materials______________ 1 e. Black light________________________ 1 /. Dark-adapted eye______________________ 1 3. Characteristics of luminescent materials__________________________________ 1 a. Radioactive materials______________ 1 b. Phosphorescent materials___________ 1 c. Fluorescent materials______________ 2 4. Applications________________________ 2 a. General____________________________ 2 b. Radioactive materials. ____________ 2 (1) Markings.-______________________ 2 (2) Signs, panels, and dials______ 2 c. Phosphorescent materials ___________2 (1) Markings, signs, panels, and dials______________________________ 3 (2) General illumination_________ 3 d. Fluorescent materials____________ 3 (1) Signs and markers____________. 3 (2) General illumination________ 3 (3) Signaling_____________________ 3 5. Precautions in selecting and using luminescent paints________________— 3 Paragraph Subject ~ Page 6. Requirements of luminescent materials. 3 a. Radioactive materials_____________ 3 (1) General______________________ 3 (2) Outdoor use__________________ 4 , (3) Indoor use_____________________ 4 b. Phosphorescent materials_________ 4 (1) Outdoor use___________________ 4 (2) Indoor use_____,______________ 4 c. Fluorescent materials_____________ 4 (1) Retention of fluorescent properties____________________________ 4 (2) Brightness limitations________ 4 7. Exciting sources______________.____ 4 a. General__________________________ 4 (1) Physiological effects of black light_____________________________ 4 (2) Considerations in selection of source____________________________ 4 b. Types..___________________________ 5 (1) Mercury vapor lamps___________ 5 (2) Argon glow lamps______________ 5 (3) Filament lamps_______________ 5 (4) Fluorescent lamps_____________ 5 (5) Natural light________________ 5 c. Allowable visible illumination___ 5 8. Construction of equipment___________ 5 9. Design approval____________________ . 5 10. Marking of approved materials_______ 6 Appendix. Glossary of lighting terms____ 6 III The following other subjects are covered in specifications prepared by the War Department: „. Street lighting during blackouts. Blackout of buildings. Blackout flashlights, lanterns, and flares (in preparation). Traffic control during blackouts (in preparation). Blackout of railroads (in preparation). Blackout requirements for highway movement. The other specifications will be published as soon as completed. The purpose of these specifications is threefold: To provide military and civilian authorities with authentic information on blackout equipment and its application. To assist commanders in insuring the military security of installations under their jurisdiction. To conserve the use of strategic and critical materials. Prepared under the direction of the Chief of Engineers, United States Army, by the Engineer Board, with suggestions of the National Technological Civil Protection Committee, the National Defense Research Committee, the National Bureau of Standards, and the War Production Board, LUMINESCENT MATERIALS !• Scope This specification describes the characteristics of luminescent materials, indicates their uses and limitations, and prescribes standards of performance which these materials are required to meet when employed to provide useful light during blackouts. Other approved methods of providing useful illumination during blackouts are set forth in the following War Department Blackout Specifications: Street Lighting During Blackouts. Blackout of Buildings. Blackout Requirements for Highway Movement. Blackout Flashlights, Lanterns, and Flares (now in preparation). Traffic Control During Blackouts (now in preparation). Blackout of Railroads (now in preparation). 2. Definitions a. Luminescent materials, — Luminescent materials are those substances which emit visible light, or can be made to emit visible light, without being heated to incandescence. b. Radioactive materials. — Radioactive materials are luminescent materials which emit visible light without external excitation. c. Phosphorescent materials.—Phosphorescent materials are luminescent materials which, having been exposed to a source of suitable radiation, continue to glow for an appreciable time after this exciting source is removed or extinguished. d. Fluorescent materials. — Fluorescent materials are luminescent materials yvhich emit visible light while exposed to a source of suitable radiation, but which cease to emit visible light as soon as this exciting source is removed or extinguished. e. Black light.—Black light is the name commonly given to the violet and ultra-violet radiation ordinarily used to excite phosphorescent and fluorescent materials, since such radiation is essentially invisible to the eye. The spectral range of black light is from 3200 to 4200 angstrom units.1 1 See Appendix for glossary of lighting terms. f. Dark-adapted eye.—The human eye is -said to be dark-adapted when it has adjusted itself for vision under low levels of illumination. Twenty to thirty minutes in complete darkness is required in order to obtain high sensitivity of vision under low levels of illumination. However, the human eye may be said to be reasonably dark-adapted when it has not been exposed to light for five minutes. 3. Characteristics of Luminescent Materials a. Radioactive materials. — Radioactive materials usually contain radium, radium compounds, or related substances. They have a very low luminosity, but furnish a sustained brightness higher than that obtainable from phosphorescent materials. When employed in dark surroundings and viewed by the dark-adapted eye, these materials are not detectable for distances much in excess of 100 feet; and, under starlight or moonlight, their apparent brightness is not much greater than that of flat white paint under the same conditions. Radioactive materials, when properly processed and protected from sunlight and moisture, will glow for several years. Since the radiation produced by radioactivity fogs photographic film, film should be stored at a distance from radioactive materials. Persons handling radioactive materials must take special precautions in order to avoid their toxic effects. b. Phosphorescent materials.—Inorganic compounds such as the sulfides of zinc, calcium, and strontium form the base of the majority of phosphorescent materials. Phosphorescent colors, initially after excitation, are usually yellow-green, bluish-green, or violet-blue. They become grayish in hue as their brightness decreases. Immediately after excitation has ceased, the useful brightness of phosphorescent materials rapidly diminishes; and an hour or more after excitation this brightness is so low that flat white paint may provide equal usefulness under illumination equivalent to that afforded by starlight or moonlight. Phosphorescent materials used under extremes of cold have low brightness but long periods of afterglow; under extremes of heat, brightness LUMINESCENT MATERIALS 1 is initially high but afterglow is correspondingly shorter. The time of excitation necessary to bring phosphorescent materials to their maximum brightness or saturation point beyond which brightness cannot be increased varies from a few seconds to several minutes, depending on the type of material, the amount of useful radiation in the exciting source, and the distance of the exciting source from the material. Sunlight, daylight, and ordinary forms of artificial illumination, as well as black light, excite phosphorescent materials. When used outdoors, phosphorescent materials usually deteriorate rapidly under exposure to sunlight and moisture. Indoors, however, these materials may retain their useful properties, for several weeks or months when correctly applied. c. Fluorescent materials.—Many organic as well as inorganic materials, including all phosphorescent materials, glow when exposed to black light. A wide range of colors is available in fluorescent materials, extending throughout the visible spectrum. The color of a fluorescent material under black light depends on the compounds from which it is made. In general, this fluorescent color is not the same as the color seen under visible light. The brightness of fluorescent materials varies with the type of material and with the wave-length and intensity of the black light used to excite them. To obtain maximum brightness, the wavelength of the black light used for excitation must correspond to the wave-length to which the particular material used is most responsive. In general, the brightness of fluorescent materials is much higher than the brightness of radioactive and phosphorescent materials, and may exceed blackout limitations. Most organic fluorescent materials, like phosphorescent materials, have little resistance to sunlight and moisture. Use of fluorescent materials requires that a power source be available for operation of the exciting unit. Fluorescent^ materials respond almost instantaneously to the exciting radiation. 4. Applications2 a. General.—Indoor uses of luminescent materials offer most promise where there is little or no illumination from starlight or moonlight. Luminescent materials are not generally recommended for continuous outdoor use. When used either indoors or outdoors, these materials should be cleaned frequently in order that their low brightness will not be obscured by dust or dirt. Since the phantomlike quality of light emitted by luminescent materials produces a sense of “stepping into space,” it is essential, when such materials are used for pedestrian pathway delineation, that they be placed as low as practicable. Because of this same quality, difficulty may be experienced in judging distances to objects illuminated with luminescent materials. Any of the luminescent materials may be made up into signs for giving directions, instructions, and identification; and in case of a sudden blackout or power failure, radioactive or phosphorescent materials (when used in adequate quantities) will provide sufficient delineation of passageways to permit orderly evacuation of a building or part thereof. b. Radioactive materials.—Since radioactive materials are costly, their use on a large scale is usually not economically justified. However, they may have limited application for the following purposes: (1) Markings.—Radioactive materials in the form of markers or tapes may be used to mark or delineate corridors, hand rails, stairs, doors, door knobs, switches, indoor obstacles such as furniture and pathways around such obstacles, outdoor obstacles, vehicles, paths to air raid shelters and first aid rooms, roadways, and similar objects and locations. Markers conforming to Corps of Engineers Tentative Specification T-1249, entitled, “Markers, Luminous (Radioactive)”, may be worn by personnel. (2) Signs, panels, and dials.—A coating of radioactive material may be placed on signs, instrument panels, and dials to provide a legible indication during periods when all light is extinguished. Transparent protective coverings over radioactive material are necessary to protect the material from abrasion and moisture and to prevent direct contact of the body with the material. c. Phosphorescent materials.—Phosphorescent materials may be procured in the form of 2 The Corps of Engineers Specifications referred to in this paragraph and paragraph 6 will be fur- nished only to manufacturers on bona fide requests submitted to the Engineer Board, Fort Belvoir, Virginia. 2 LUMINESCENT MATERIALS tape, cloth, plastic, decalcomania transfer, or paint. If a high degree of continuous visibility is required, these materials should be excited at approximately half hour intervals. Possible applications for phosphorescent materials are as follows: (1) Markings, signs, panels, and dials.— Phosphorescent materials may be used for the same purposes as indicated for radioactive materials in sub-paragraph b above, provided some means of periodic excitation is available. When signs incorporate phosphorescent materials, the legend must be simple in form and as large as possible in order to obtain maximum legibility. (2) General illumination.—Phosphorescent materials may be used to provide a very low level of general illumination, but this use is not widely applicable because such illumination is of little aid to detailed work, and decreases rapidly after the exciting source has been extinguished. However, if several square yards áre furnished in an air raid shelter, for example, even the small amount of light emitted from this area will materially add to ease of mind of the occupants in case of a power failure, thereby helping to avert panic. d. Fluorescent materials.—Use of fluorescent materials during blackouts is necessarily limited because such materials require continuous excitation by special sources of black light. Moreover, transformers and other auxiliary equipment required for most sources of black light, use strategic and critical materials. Sources of black light (see par. 7) may be energized from available power lines or portable batteries. Possible blackout applications of fluorescent materials are discussed below. (1) Signs and markers.—Any of the fluorescent materials may be made into signs and markers. However, white paint, reflector units, or reflectorized material,3 used in conjunction with visible lighting units which conform to blackout requirements,4 are usually more suitable for this purpose. In cases where there is a possibility of failure of the exciting source, radioactive or phosphorescent materials will give greater certainty of performance. (2) General illumination.—Indoor incandescent blackout units5 will provide general in terior illumination more efficiently than will a combination of black light and fluorescent materials. (3) Signaling.—Mercury vapor lamps (see par. 7b) installed in reflector units equipped with filters and shutters may be used to project a beam of black light on a fluorescent screen for purposes of signaling. 5, Precautions in Selecting and Using Luminescent Paints The toxic properties of radioactive paint and its high cost preclude its use for large applications. Luminescent paints of the phosphorescent and fluorescent types are difficult to apply. They may be either brushed or sprayed, but must be used in accordance with the manufacturer’s instructions in order to obtain maximum durability and luminous efficiency. The use of new, clean brushes is essential when the paint is applied by brushing. Protective coverings and undercoats should be used to protect luminescent coats from moisture and sunlight. Greater brightness is ordinarily obtained by use of white undercoats; however, lead pigment paints should not be used. Transparent varnishes which do not “yellow” with age and which do not react with the luminescent material should be used for protective coverings; and the protective covering as well as the undercoat should be specified by the manufacturer. In making a luminescent paint, the liquid or vehicle must be highly moisture resistant and free of acidity, and in some cases its selection will depend on the pigment with which it is to be used. In general, metallic driers should be avoided. When their use is necessary, they shoul4.be used in as small amounts as possible. Most of the well-known paint solvents can be safely used in luminescent paints; those which have an acid reaction, or which may decompose to form acids, should be avoided. 6. Requirements of Luminescent Materials a. Radioactive materials—(1) General.— For all uses, radioactive materials shall be sealed within or under suitable transparent protective covers which will prevent chipping and 3 See Corps of Engineers Tentative Specification, “Reflectorized Coating System.” * See War Department Specification, “Blackout Requirements for Highway Movement.” 6 See War Department Specification, “Blackout of Buildings.” LUMINESCENT MATERIALS 3 disintegration of the radioactive material. These -covers shall be durable and shall possess low moisture absorption qualities. Radioactive material should be stored as far as possible from photographic film. Lead lined boxes shall be used to store large quantities of radioactive materials. Whenever the covering over radioactive materials is damaged, the device containing these materials shall be buried or otherwise safely and permanently disposed of. Under no circumstances shall damaged devices containing radioactive materials be placed or left where possibility exists that the radioactive compound contained therein might be taken internally by any person. (2) Outdoor use.—Radioactive markers for outdoor use shall conform to Corps of Engineers Tentative Specification No. T-1249, “Markers, Luminous, (Radioactive).” When designed for other outdoor purposes, radioactive materials shall have weathering and brightness characteristics that are equal to those specified for markers in the above named specification. (3) Indoor use.—Radioactive materials designed for indoor use shall have a brightness value 200 days after' compounding of not less than 7.4 micro-lamberts. The method of measuring brightness shall conform to that set forth in Corps of Engineers Tentative Specification No. T—1249. Workmanship throughout shall be of the highest grade and in accordance with the best standard practice. b. Phosphorescent materials.—(1) Outdoor use.—For outdoor uses, phosphorescent paint shall conform to Corps of Engineers Tentative Specification No. T-1225, “Phosphorescent Coating System.”^ Other phosphorescent materials to be used outdoors shall conform to the brightness, decay, and weathering standards outlined in test descriptions for coating systems in Corps of Engineers Tentative Specification No. T-1225. (2) Indoor use.—Phosphorescent paints for indoor use shall conform to Federal Specification, “Non-Radioactive Luminous Paint (Phosphorescent Types).” 6 Other phosphorescent materials for indoor use shall conform to the brightness, decay, water sensitivity, and weath ering standards as set forth for paint in the above-named specification. c. Fluorescent materials.—(1) Retention of fluorescent properties.—Fluorescent materials shall retain a luminosity of not less than 50 percent of their original value after having been subjected to a standard weathering test for 100 hours. This test shall be similar to that specified for phosphorescent paint, except that the brightness shall be checked by the visual comparison method. (2 ) Brightness limitations.—Since fluorescent materials can be excited to such a degree that light emitted therefrom is visible to aerial ^ observers, limitations on brightness are necessary. When fluorescent materials are used for providing general illumination in building interiors, at locations where their glow can be observed from outside the building the surface brightness of these materials shall not exceed 0.001 footlambert. Surface brightness of fluorescent materials used to provide general illumination out-of-doors shall not exceed 0.0001 footlambert. However, greater brightnesses are permitted on small vertical surfaces, provided such brightnesses do not exceed the values tabulated below: Maximum diame- Allowable bright- ter of area (feet) ness (footlamberts) 0 to 2 0. 0120 2 to 4 0. 0030 4 to 6 0. 0016 7. Exciting Sources a. General.—(1) Physiological effects of black light.—The black light necessary to excite fluorescent materials causes the cornea and lens of the eye to fluoresce strongly, thereby interfering with vision and producing discomfort after short periods of exposure. Ultraviolet radiation of wave lengths lower than 2800 angstrom units is harmful to the eyes and skin. (2) Considerations in selection of source.—Various types of sources are available for exciting fluorescent and phosphorescent materials. The major considerations in choice of an exciting source are the type of material to be excited and the purpose, extent, and location of the application. In outdoor areas where there 6 This specification is now in preparation and will soon be available from the National Bureau of Standards. 4 LUMINESCENT MATERIALS is danger of aerial observation, the use of black light sources emitting little or no visible radiation is to be preferred for exciting fluorescent and phosphorescent materials during blackouts. On the other hand, black light sources emitting considerable visible light may be used in buildings where openings are properly obscured.7 b. Types.—(1) Mercury vapor lamps.— Mercury vapor lamps are the most efficient sources of black light available. Radiation from such lamps is easily filtered to produce black light. Various sizes of mercury vapor lamps are available, ranging in wattage from approximately 100 watts up to several thousand watts. The low-wattage lamps may employ a special bulb which filters out nearly all visible radiation. Mercury vapor lamps require special transformers for satisfactory service and necessitate an alternating current power supply or special auxiliary equipment to permit operation from direct current. Since a “warming up” period of several minutes is required, these lamps cannot be switched on and off quickly. Additional disadvantages are their high cost and their use of strategic and critical materials. (2) Argon glow lamps.—Argon glow lamps provide a much weaker source of black light. Because of the low light output of such lamps, filters are usually not required. Argon glow lamps are rated at 5 watts or less, and because of their low current consumption, these lamps may be incorporated in portable battery-powered units. For continuous operation, argon glow lamps should be burned at their voltage rating of 105 to 125 volts; although they will operate on voltages as low as 65 volts for alternating current and 90 volts for direct current. No transformers or other external auxiliary equipment are ordinarily required. Unlike mercury vapor lamps, argon lamps do not require a “warming up” period and may be switched on and off instantaneously. (3) Filament lamps.—Ordinary tungsten filament lamps are relatively inefficient sources of black light and require filters of high absorption values to eliminate visible light. However, lamps such as the photo-flood types, which operate at higher temperatures (and therefore have a very short life), are slightly more efficient. Unfiltered filament lamps excite phosphorescent materials and may be used indoors for this purpose during blackouts, provided the use of such lamps meets all requirements of the War Department Specification, “Blackout of Buildings.” Ordinary flashlights equipped with special filters provide a portable source of extremely low intensity black light. (4) Fluorescent lamps.—Fluorescent lamps may be used in the same manner as filament lamps. Their efficiency as an exciting source, however, is much greater than that of filament lamps. Special types of fluorescent lamps rated as low as 12 volts and 3 to 4 watts are available. Auxiliary equipment is needed for the operation of fluorescent lamps. (5) Natural light.—Sunlight and daylight will excite phosphorescent materials. Phosphorescent materials so exposed will continue to glow after darkness, although their brightness will decrease considerably during the period of twilight. c. Allowable visible illumination.—The source used for exciting luminescent materials in the interiors of buildings shall be completely invisible outside the building. Black light sources used to excite luminescent materials out-of-doors shall be shielded in such a way that no visible light from the source can be seen above the horizontal. Visible light produced by outdoor sources shall not exceed 0.1 lumen, and the brightness of any surface illuminated by such visible light shall not exceed that specified for fluorescent materials in subparagraph 6c (2). 3, Construction of Equipment Materials and equipment specified herein shall be of rugged construction and shall not be readily subject to derangement, tampering, or misuse in service. Use. of strategic and critical materials shall be avoided wherever possible. 9» Design Approval Approval of materials and equipment specified herein, including such instructions for use, handling, storage, and disposal as should be supplied therewith, shall be based on reports submitted to the War Department by a testing laboratory accredited by the War Department. A list of the laboratories which have been accredited as of this date is attached hereto, but does not constitute a part of this specification. 7 See War Department Specification* “Blackout of Buildings,* LUMINESCENT MATERIALS 5 IO. Marking of Approved Materials War Department approval of any material or article of equipment specified herein, which is manufactured for blackout use, shall be indicated by a marking which includes the words, “BLACKOUT (insert material designation)—W A R DEPT. STANDARD.” There shall also be displayed a code number, to be assigned by the War Department at time of approval, which shall be placed directly beneath or after the word “Standard.” This marking, together with the manufacturer’s name, shall be placed on each device or each unit of approved material at a location which will facilitate inspection. If a fluorescent material requires a specific activating source in order to conform to the requirements set forth herein, the proper source to be used therewith shall be indicated on the material or device. APPENDIX GLOSSARY OF LIGHTING TERMS Angstrom unit.—The angstrom unit is a unit of length equal to a hundred-millionth of a centimeter, used in expressing the length of light waves. Candle.—The candle is the unit of light intensity. The unit used in the United States is a specified fraction of the average horizontal candlepower of a group of 45 carbon-filament lamps preserved at the National Bureau of Standards, when the lamps are operated at specified voltages. Candlepower.—Candlepower is light in tensity expressed in candles. Footlambert.—The footlambert is a unit of brightness equal to the average brightness of any surface emitting or reflecting one lumen per square foot. Lambert.—The lambert is a unit of brightness equal to the average brightness of any surface emitting or reflecting one lumen per square centimeter. Lumen.—The lumen is the unit of light quantity. A uniform point source of one candle emits 12.56 lumens. Micro-lambert.—The micro-lambert is one millionth of a lambert. LABORATORIES ACCREDITED BY THE WAR DEPARTMENT Electrical Testing Laboratories, Inc^ New York City, New York. IL &. GOVERNMENT PRUTTING OFFICE: 1942 LUMINESCENT MATERIALS