Light signals: A discussion of the optics, sources of illumination, and most efficient distribution of light for railway signals giving day and night indications
✍ Scribed by C.O. Harrington Jr.
- Publisher
- Elsevier Science
- Year
- 1914
- Tongue
- English
- Weight
- 856 KB
- Volume
- 177
- Category
- Article
- ISSN
- 0016-0032
No coin nor oath required. For personal study only.
✦ Synopsis
THE corrugated lens is generally used for signal lights on account of its cheapness, small weight, and more uniform cross-section . Where colored glass is used a fairly uniform cross-section is desirable, as otherwise the centre of the lens would be decidedly darker than the periphery. The corrugated lens is better adapted to pressing, and, as the expense of grinding is prohibitive in the case of signal lenses, the accuracy with which the corrugated lens can be pressed or moulded is a point in its favor . In Fig . , -d represents a typical corrugated signal lens, and B represents a solid double convex lens having the same diameter and focal length ; note the lighter construction and more uniform cross-section of A . For a more detailed discussion of the signal lens the reader is referred to a paper entitled " The Optics of the Signal Lens," by Dr. William Churchill (Railzeut.V Signal Association .
Annual Proceedings, IyoO .
Assuming a source 0, Fig. , projecting light equally in all directions : the fraction of the total spherical candle-power pro-
jeered by the lens is-2 2 , and therefore increases with the angle B which the lens subtends . B is known as the " aperture " of the lens, and is limited by the total reflection of ray OX in the direction XS when the deflected light AX strikes the convex face of the lens at the critical angle . For the ordinary . smooth-face " lens common practice has fixed So' as the greatest value of B . chiefly with the purpose of Continued from page 408 . 54I