. Electric railway journal . ector being perfect, theactions of a lens and a parabolic reflector are as shownin Figs. 1 and 2 respectively. Figs. 3 and 4 show respectively the actions of a lightsource of appreciable size on a lens and a parabolicreflector. A cone of light strikes each small surface ofthe lens or reflector and is reflected or refracted as acone of light, the angle of divergence of which is ex-actly equal to the angle subtended by the light sourceitself. The effect of focal length upon the angle ofdivergence of a beam is shown in Figs. 5 and 6, whichrepresent two parabolic refle
. Electric railway journal . ector being perfect, theactions of a lens and a parabolic reflector are as shownin Figs. 1 and 2 respectively. Figs. 3 and 4 show respectively the actions of a lightsource of appreciable size on a lens and a parabolicreflector. A cone of light strikes each small surface ofthe lens or reflector and is reflected or refracted as acone of light, the angle of divergence of which is ex-actly equal to the angle subtended by the light sourceitself. The effect of focal length upon the angle ofdivergence of a beam is shown in Figs. 5 and 6, whichrepresent two parabolic reflectors of equal diametersbut different focal lengths. The intensity of illumination given by any headlightdepends upon the following: Concentration of the pri-mary light sources at the focal point of the lens or re-flector; shape and condition of the reflecting or re-fracting medium, and candle-power of the light source. Figs. 7 and 8 illustrate the effect of concentrationof the light source. These represent two reflectors of. FIG. 9—DIAGRAM SHOWING CONCENTRATION AND DIFFUSIONOF LIGHT RAYS BY REFLECTOR equal diameter and focal length, but in one case a smalllight source is used, resulting in a narrow beam oflight, while in the other the large light source producesa beam of considerable divergence. If the reflector is tarnished or the lens is dirty lightwhich would otherwise be transmitted is absorbed. Ifthe refljctor or lens is not true, the beam will be moredivergent and of less intensity. It is also perfectlyobvious that if the reflectors are equal in efficiency andhave the same dimensions, the higher the intensity ofthe light source the higher will be the intensity of theprojected beam. Fig. 9 shows how the entire beam of a headlight ismade up. The center of the reflector is the most ineffi-cient part, while the main beam (the shaded section),which is useful for long-range illumination comes fromthe outer portions of the reflector. If it is desired touse a combination lens
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