Document zz8pY4Jp6RRLbmLrZ6Lj5x7Y0

LIGHTING -FOE SEEING 759 SLsuch factors must be kept in mind when lighting recommendations are ^nffdewEconomic aspects, of course, are important and may require some compro^{nsvglNevertheless, unless proper weight is given to ease of seeing, visibility, and ___ dfil visual capabilities, light and lighting will not be accomplishing the Inriirlary pmpose of providing quick, accurate, safe, and comfortable seeing. VII. Light Sources A. FILAMENT LAMPS fe^wFilament lamps emit essentially black body radiation generated by an. elecIK heated filament. This radiation is continuous throughout the visible and fefrared regions of the electromagnetic spectrum48 (Figure 11). The peak *' pn is generally in the infrared region, only a portion of the energy being j in the visible region as light. Since this peak shifts toward the visible |n as the filament is operated at a higher temperature, hotter operation , pro- "whiter" light and makes the lamp a more efficient light source. However, ^increases the rate of evaporation of the filament, decreasing the life of the ^Therefore, in the design of incandescent light sources, such factors as ecoe and application of the lamp. are considered in determining the most deiicompromise between efficiency and lamp life. For example, where lamps are I'nsive compared to the cost of electrical power, the shorter-life, higherSncy lamp should be employed. On the other hand, where lamps are. costly 'or costs of replacing them are high, a longer life is more economical. For grsphrc~projectian--lamp~applicationB"wbere-a~large quantity of "white" ||i.needed, lamps are operated at relatively high efficiency with correspond|f|horter life (5 to 50 hours). [he first practical incandescent electric lamp was developed by Thomas A. | in 1879. It consisted of a filament of carbonized thread enclosed in a glass ipe from which the air had been evacuated. Since that date many improveShave been made through active research and dd^elogment to obtain the jraescent lamp as it exists today. One of these milestone^was the.development gfilament made of tungsten wire, providing higher.efflciency and longer lamp BKeLamp efficiency has been further -in^pa^^ljhrpugh^piitaaiy developments, inHH*"|;the double and triple coiling'of- filaments, which reduces heat,.transfer frqm-the-filamenl^Mbre^rec'lhtiy4"hew-process-of:<`Q-coa;tihg!5--ha's'been |8'tb give almost perfect diffusion of light from the bulb with no sacrifice in \ Control of light output has been obtained with the introduction of re|r.:lamps. For these lamps a glass bulb is formed to the. demred'cShtour and ecUon,the,inside with a;thiri.film of.highly reflecting silver. B. MERCURY LAMPS Gaseous discharge lamps were made practical about 1900 with the developgroftf the Cooper Hewitt low-pressure mercury-arc tube. This lamp is the predfe- j?Lamp bulletin, Bulletin LD-1, Lamp Division, General Electric Co., October, 1950.-