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Patented Feb. 21, 1939      2,147,679

UNITED STATES PATENT OFFICE
2,147,679
ILLUMINATING SYSTEM

Charles I. Stanton and Edgar O. Seaquist, Washington, D. C., assignors to the Government of the United States of America, as represented by the Secretary of Commerce

Application November 16, 1936, Serial No. 111,078

3 Claims. (CI. 240--1.2)

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757)

The invention described may be manufactured and used by or for the Government for governmental purposes without the payment to us of any royalty thereon.
This invention relates in general to lighting systems and more particularly to systems for illuminating runways at airplane landing fields, or other flat surfaces.
The conventional landing area floodlight system employs one or more reflector or refractor floodlights disposed at elevated positions with respect to the terrain toward which the light rays are directed. This type of system is disadvantageous for several reasons. In the first place even in clear weather the illumination varies inversely as the square of the distance from the light source. Hence the luminous intensity of the light is of necessity extremely great in order to properly illuminate the entire area of a long and adequate landing strip. Secondly the airplane pilot is subjected to the glare inasmuch as he ust at times face the light in landing or taking off. Moreover, in foggy or rainy weather with the floodlight unit mounted high above the ground necessary for advantage in illumination of the surface, the illuminate fog or rain tends to give the pilot a false impression as to his position above the ground. At best the conventional system produces glare and shadows that interfere with the pilot's clear vision.
It is therefore an object of this invention to provide a lighting system that will overcome the foregoing objections and properly and adequately illuminate the landing strip to be used, enable the pilot to land or take off without ever being forced to look directly into the light and which system will provide for a definite and considerable restriction of the height of the light rays above the actual surface of the landing strip.
In order to accomplish the above and other objects the invention contemplates the use of a plurality of floodlight units disposed at spaced points along the lengths of the landing strip. In order to confine the illumination to the ground surface and restrict the height of the light rays above the landing strips surface, the units are designed so that the light source is below the ground. The light is reflected upwardly and concentrated as it passes through a small outlet in the underground portion of the unit. Above the light outlet is a low reflecting system which is so designed as to reflect the light in rays, substantially all of which are nearly parallel with but slightly incline downward toward the ground. The part of the reflecting system disposed above the ground is of light weight and of easily destructible material which would not cause injury to the airplane in cast the later should collide with it. These units are placed in such a position with respect to the runway that the pilot need never look directly at the units as he watches the runway ahead of in in landing or taking off.  In other words, the units may be placed either on both sides of or down the middle of the runway and in withe case the pilot lands or takes off in a direction parallel with the series of units, rather than toward or away therefrom. The invention contemplates the use of different runways to correspond with prevailing wind conditions and the equipping of each of the runways with such system of floodlight units.
The invention is set forth with greater particularity in the following specification and appended claims, certain embodiments therein being illustrated in the accompanying drawings, in which: 
Figure 1 is a top plan view of one form of the floodlight unit providing for an area of reflected light throughout an arc of less than 360 degrees.
Figure 2 is a view in vertical section through the same unit taken along the line 2-2 of Figure 1.
Figure 3 is a front view in perspective of the upper part of the reflector system shown in section in Figure 2.
Figure 4 is a view in vertical section through a modified form of floodlight unit providing for an area of reflected light throughout an arc of 360 degrees. 
Referring more particularly to the drawings, in Figure 2, the device comprises a casing 1 arranged below the level of the runway surface 2. In this casing is suitably mounted an electric lamp 3 as a source of light. The electrical leads 4 may extend through an outlet 5. The casing has a cover 6 removably held in place by screw bolts 7, the cover being provided with a central aperture 8. The casing also has mounted therein reflector 9 for directing light rays upwardly from beneath the ground surface through the aperture 8.
In addition to the foregoing there is also provided a reflector assembly above the ground. This comprises a plate 11 bolted to the cover 6 at 12, and a cup reflector 13, another reflector 14 and flat annular stray light shield and reflector 15 supported on the plate 11 by the flat supports 16 set radially from the vertical axis. The reflector 14 is shown as an upward extension of the cup reflector 13 and it extends upwardly and outwardly. The under surface of a reflector 14 is the reflecting surface and it may be a straight upward incline but the preferred for is to have
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