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Polygonal Floodlight Mirror — Benford and Palmer 111
The convergent form of the beam is also accompanied by the secondary effects as follows:
(1) An abnormal loss of light due to the convergent beam falling on the mechanism of the lamps heads ;
(2) An overheating of the front door that is occasionally used. In cases of extreme convergence the glass may be heated nearly to the melting point, with a severe loss in clearness and transmission;
OPTICAL DIAGRAM USE OF A PARABOLIC MIRROR TO OBTAIN A FLOODLIGHT BEAM
CON[/£RGENT BEAM FIG. I
DIVERGENT BEAM FIG. 2
Fig. 1 — Optical sketch of light source placed to give a convergent beam from a paraboloid. This arrangement does not involve a loss of light on the inside of the barrel, but the interference of the head mechanism may be serious.
Fig. 2 — Optical sketch of light source placed to give a divergent beam. There is here considerable interference by the barrel. The lamp heads may be lowered to throw the lamp shadow towards the outer part of the beam.
(3) A decrease in the amount of light incident upon the mirror.
The alternative plan is to move the lamp closer to the mirror. This, in general, produces the same results as before, with certain variations that are easily recognized. There is a loss of light in the beam because the extra Hght that falls upon the mirror is reflected onto the inside of the barrel, and even some of the light that is ordinarily useful is lost in the same way. In the typical case illustrated in Figs. 1 and 2 the parallel beam being made equal to 100, the convergent beam as it leaves the effective part of the mirror is 90, and the divergent beam is 72. In a particular design to be noted later the barrel loss was about twice as great as in this example. Thus