INSIDE FROSTING

Evening Star, Issue 19663, 16 September 1927, Page 2

INSIDE FROSTING

TWENTY YEANS’ EXPERIMENTING EXPERTS LAUD RECENT DISCOVERY Top place among all American organisations of professional electrical experts is generally conceded to the American Institute of Electrical Engineers. Anything which this body, or any of its committees, has to say on the subject of lamps or lighting is received therefore with unusual attention. Recently tho institute’s Committee on Production and Application of Light contributed to the ‘ A.I.E.E. Journal ’ an article on ‘ Inside Frosted Lamps 1 which is instructive and interesting. “ Growing appreciation of the importance of good electric lighting during tho depado between 1915 and 1925 led to much wider use of diffused light. Diffusion by enclosing the lamps in translucent glassware and adequate shades and by using other devices was a vague subject to the general public, 1 comments the committee, leading up to the general subject of lamp frosting. “ Consequently with tho advent of tho ■ high-efficiency tungsten lamp, the manufacturers endeavored to conceal the bright filaments by etching or frosting the bulbs. Frosting on tho outside of tho bulb proved objectionable for two chief reasons. It was wasteful of light, offsetting to a slight degree the great progress made in increasing the lightproducing efficiency of the filament. Also, outside frosted lamps collected dust and dirt quickly, which could not easily bo wiped off. “ For many years lamp engineers realised that a lamp frosted on the inside instead of on the outside would bo very desirable. It would not only present a smooth outside surface and ho as easily cleaned as a clear lamp, but a lighter frosting would suffice, increasing tho efficiency. Tho trouble with the idea was that when a lamp bulb was frosted on the inside, it became as brittle ns an eggshell. For twenty years engineers wrestled with this problem. to no avail, until Marvin Pipkin, of tho Genera! Electric Company at Nela Park, solved tho difficulty. Tho method is simple. “A strong solution of _ acid is first sprayed into tho bulb, which etches it. In this condition the surface of the glass is made up of irregular little projections with many sharp angles. While tho glass is still in this state it is extremely weak, and a slight pressure or bump is sufficient to shatter it. So far tho process is similar to Inrmcr attempts at inside frosting. The difiorence lies in tho strengthening process, which is the application of another acid solution, somewhat weaker than the first. This second treating rounds off the sharp edges and minute projections, giving the glass an appearance under a powerful microscope of being made up of tiny hemispheres. The bulb is now strong again—just as strong ns it was originally. “ Superiority of the inside frosted lamp over tho outside frosted, so far as liaht transmitting characteristics are concerned, also needs explanation. In tho outside frosted lamp light from tho filament travels through the gas or vacuum to the wall of tho bulb, then through tho glass, on the outer surface of which it meets the frost. Then. depending upon the direction of the plane of the particle of rough surfaces, the beam either passes on through the frosted surface as useful light, or is reflected back through the glass layer. Each time the light passes through a certain amount of absorption occnis. “ Diffusion of tho light by the inside frost is obtained by prismatic refraction with comparatively little loss. In fact, the inside frost allows an even greater portion of tho < light to pass through than does a similar frost on the outside of the lamp. This is due to the fact that the multiple internal reflections are not so numerous in t m inside frosted lamp, because the i^W 1 ; interior surface docs not re fleet < J considerable portion of the light bacl and forth inside the lamp, as happens with the outside frosted lamp- Mmcover the relative absorption of the inside frost does not increase so rapidly with the life of the lamp as does that nf other diffusing media. . << For these reasons, tnen, Uio insidcfrosted lamp is 01ll y ab . o,lt ' I,cr less efficient than a clear lamp, eon trusted with a loss of efficiency of three to four times this muchi in the old st 3 sand-frosted and sprayed lamfio. “ \nother groat benefit of the discovery of inside frosting is at once apparent when it is realised that now the manufacturers need only one J'hnips lamp of each wattage instead ofta) will several different finishes. Hus. beneficial not only from tho standpomt of economies resulting froin tho m creased use of automatic machinery and the decreased investment m idle in warehouses and on aeaieis shelves but also there is still greatoi benefit’for the public in general, bimx the inside-frosted lampsgivoprectma „„ much Imht as clear lamps, they can be used to replace clear lamps for every ordinary 1 use! This means that whenever, because of ignorance or cnreW i, ' s, ' si IOS .I Of tlio iiisiao-trosUoS IzitXirorrsnfi.r matic research, persistently pursued.