Document LJggobpd6obq1dpr2rQqdw8dg

760 S. K. GUTH AND E. A. LINSDAY cessor of the present-day mercury and fluorescent lamps. In general, today's mer-jf cury lamps are about twice as efficient generators of light as the filament lamps However, there are advantages and disadvantages to both that affect the choice of lamp type for any specific application. High-pressure mercury lamps have the objectionable characteristic of delayed! starting and restarting. Several minutes are required for the lamp to reach full brightness, and in case of a momentary power interruption, the lamp will nd|i restart until the arc tube has cooled sufficiently for the mercury vapor to condense* --a matter of about 5 minutes. These disadvantages are partly overcome by iiS stalling filament lighting along with the mercury, to provide illumination during the brief periods that the mercury lamps are inoperative. One of the most rece.n|| improvements.in mercury lamps is the addition of a phosphor coating, which congi verts part of the mercury radiation to light in the red region of the spectrui|| When combined with the,bluish green light from the mercury arc, color renditif) of objects viewed under this source is improved markedly. C. FLUORESCENT LAMPS Fluorescent lamps, first introduced commercially in 1938, have become ,Ji|| creasingly popular in recent years. Today, more illumination for general light purposes is provided by fluorescent lamps than by all other sources combing The rapid growth of this type of lighting is due in part to the trend toward higra levels of illumination. Fluorescent lamps are about three times as efficients filament lamps. Basically;; a fluorescent lamp -consists-of- a~low--pressure-mercury^arc-rra'l through which current flows, causing the mercury vapor to radiate invi'Mg energy.44 This radiation in turn activates the phosphor coating on the insidej|c the glass tube, converting this energy to visible light. The lime-glass tube filte out all radiation that would be harmful to the eyes or skin. --.M Until recently fluorescent lamps were started by means of a starter for.eS lamp, which heated the electron-emitting cathode in each end of the lamp. recent developments have made it possible to eliminate this starter switch. Wm ern fluorescent lamps are started either by ballasts having sufficient voltage start the lamp instantly or by ballasts having auxiliary windings that heat;:||j cathodes very rapidly to emitting temperature. This latter type of operation called-Hapid-Start-.- Fluqrescent lamp life,48 unlike filament lamp life,, is not:-limiteddjyfll efficiency. Consequently, fluorescent lamps are designed to give much-loftf service (7500 hours). However, lamp life is affected by the number of timeSl .lamp is started. The,.75Q0-h.o.ur.Jif&jatiagjs..,based on.3.,hours ,p,f-.lamp....o.pe; per start. More frequent starting will reduce the life span, whereas lamps will longer if started less frequently. D. GERMICIDAL LAMPS Germicidal lamps are basically the same as fluorescent except that novjjn| " C. L. Amick, Fluorescent Lighting Manual. McGraw-Hill, New York, 1942. (flfi "R. N. Thayer, Determinants of fluorescent lamp life, Ilium. Eng., 49, 527 (1954).' Vis LIGHTING TOR SEEING 761 fior is used on the tube. Disinfection of air, water, pharmaceuticals and so forth, i germicidal lamps, is accomplished by making the lamp of a special glass that $$8 the short-wave ultraviolet energy to irradiate the product. Care should be j^ercised to avoid exposure of the skin and particularly the eyes to this energy. E. INFRARED LAMPS ||Tnfrared lamps48 are filament lamps designed to heat areas of the body or t products, such as painted surfaces, textiles, and metal parts. Any filament |i|.i8 an efficient source of infrared energy. Infrared lamps are usually designed e a long life (5000 hours); they are not designed to produce light efficiently. VHI. Lighting Benefits IfjifThe trend in lighting application is continually toward better seeing condiionsj47 With the understanding of the importance of balanced brightnesses4? and ||nmiized glare in industrial areas, and the development of better techniques of "milling light, higher lighting levels have become practical and highly desir- fjgj'Figure 12 shows the increase in illumination levels recommended for indus- r------------ -------------- 1-------------- 1-------------- :-------------- 1-------------- 1-------------R!ICOMME NDED LEVELS OF GENERAL ILLUMINATION nLAO i jggs ..`jwj r year;. * 1 1 1 Vi-, trtw .'V FLUORESCENT.,,,. M E-R`6^RY^>J W |pre 12. The steady increase in levels of illumination recommended- -^industrial area's' lie past 40 years. Recommendations ranged between the lower and upper solid linesi di, lines show dates of introduction of new types of lampB. iJSr p$C. E. Egeler, Infrared lamps at work, Magazine of Light, 20, 8 (February, 1951), 1 . ppE. A. Linsday, The industrial lighting look, Magazine of Light, 23, 9 (May-Jjineivl954)! 'f^E. A. Linsday, Revolution in lighting, Natl Safety News, January, 1954. *'* )i II t\