US1746399A - Reflector - Google Patents

Description

Feb. 11, 1930. w, UTTLE 1,746,399

REFLECTOR Filed Dec. 1.1925 2 SheecS-Sheet 1 INVENTOR xii/Z4,

0 BY a/z zw 3 ATTORNEY Feb 11-, 1930.

w. F. LITTLE 1,746,399

REFLECTOR Filed Dec. 1. 1925 2 sheets-sheet 2 l NVENTOR QBY Patented Feb. 11, 1930 v UNITED STATES WILLIAM E. LITTLE, OF NEPPERHAN HEIGHTS, NEW YORK REFLECTOR Application filed December My invention relates to reflectors for incandescent lights and is particularly adapted for use in automobile headlights railroad signals, flash lights, or the'like. An object of my invention is to provide a reflector giving suflicient vertical spread to properly illuminate the roadway without producing undue glare in the eyes of an approaching motorist, and to produce a beam of relatively Wide spread having a nearly uniform crosssection, such as is desirable for signal and flash light beams.

Another object is to provide a reflector of such character as to accommodate itself to commercial variations in incandescent lamp bulbs, Without requiring refocusing and without substantial variation in the illuminating properties of the resultant beam. In other Words, I produce a set-focus reflector.

A further object is to provide a reflector of such character that even with the light source located slightly on either side of the focal point, the nature and spread of the field of light will be maintained substantially uniform.

A further object is tominimize the upward rays of light so as to reduce glare.

Experience has shown that the beam projected from the parabolic reflectors in common use (1% inch focal length) with standard types of automobile headlight, are of insufficient vertical spread to properly illuminate the roadway. It is therefore customary to make use of additional means for increasing the vertical spread.

The parabolic reflector projects a beam approximately 2 vertically by 3 horizontally (the elliptical shape being due to the construction of the filament). If this beam is merely widened horizontally, a narrow band of light is projected across the roadway, leaving the nearby and extreme distance (150 feet and beyond) in darkness.

vIn addition to the objection of projecting a narrow beam, the parabolic reflector is extremely sensitive to focal adjustment because the center of each cone of light projected by any part of the. reflector falls in the center of the beam, and the cones superimpose, and

therefore all cones overlap, those from the 1, 1925. Serial No. 72,475.

center of the reflector being of greater angular spread than those from the edges. The slightest movement of the light source will cause the cone axes to cross or diverge and produce a dark center in the beam.

To remedy the defects referred to in the parabolic reflector and provide a reflector projecting a beam of suificient vertical spread and less sensitive to focal adjustment, my reflector has been designed in such a way that each element of the reflector will project a fan shoped beam subtending the desired angle of spread, rather than each infinitesimal area of the reflector projecting the beams with parallel axes. I

In orderthat m invention may be better understood, attention is directed to the accompanying drawings in which:

Figure 1 is a vertical side sectional view of my improved reflector with an incandescent light and socket located therein in the usual manner, i. e., arranged so as to be coincident with the reflector axis;

Figure 2 is a vertical front view of the same reflector showing it to be symmetrical and with the lamp axially arranged and also showing the location of the name or trade mark or other printing for the purpose of dulling the reflector surface to reduce the upward rays of light from this portion;

Fig. 3 is a vertical sectional view of my improved reflector and is a modification of Fig. 1 showing the preferred location and position of the incandescent lamp;

Fig. 4: is a plan view of Fig. 3 showing the preferred arrangement employing vertical or nearly vertical flattened sections;

Fig. 5 is a vertical sectional view of my reflector showing the characteristics of various portions ofthe reflector surface; and

Figure 6 is a vertical sectional view illustrating the principle underlying the construction of my improved reflector, said principle being applied to my reflector in which for purposes of illustration, the generating element is in the form of a hyperbola.

To meet the requirements of the best type of headlamp, the beam must be uniformly bright, or nearly uniformly bright throughout its diameter and its limits must be well defined. Furthermore, the beam should have a spread of at least in order to cover a sufficient area along the road.

To allow for manufacturing inaccuracies, fila'ment distortions and the like, every art of the beam pattern must receive light rom more than one section of the reflector. Therefore, there must be superimposition of light cones from op osite sections of the reflector.

In my re ector the opposite elements project beams that superimpose, thereby causing suflicient overlapping to eliminate filament ima es and other irregularities of like nature. bus, in Fig. 5 the rays reflected for example from point A superimpose over the rays reflected from point B, while the rays reflected from points C and D also superimpose. This holds good for corresponding points in the element on one side of t e axis which superimposes with the corresponding points in the element on the opposite side of the axis. 1

The construction of my reflector is such that the most sensitive part to focal adjustment (namely, that between and 75 to the reflector axis measured from the reflector vertex, or that zone of the reflector aproximately embraced within the brackets F. and E) reflects lights to the center of the beam, whereas the rest of the reflector surface projects light to the outer edge of the beam.

With this construction approximately half of the rays projected from each element from the center half way out) cross the reector axis. The remaining rays (from half way out to the edgeg are divergent thereto. Thus, for the same ocal length the crossing over of the beams from opposite elements permits of a deeper reflector, of if the reflector is not deeper, the arrangement permits a greater focal length.

' It will be seen, therefore, that a reflector of this design can be made to cover any desired angle of spread, and that for the same diameter and same focal length will have a greater depth and subtend a greater solid angle of light flux. 1

s the reflector can be made to produce any desired spread, and as experience has shown that a spread of 5 is desirable, each element of the reflector is designed to project beams to cover 3, the physical size of the filament (providing the two additional degrees of sprea As the greater the focal length of any reflector the less its sensitiveness to focal adjustment, my reflector may be provided with a greater focal length, at the same time subtending the same solid angle of light flux as the standard parabolic reflector. I proose making a reflector utilizing a focal ength of one and one-half inch, instead of the standard parabolic focal length of one and one-quarter inch.

The portion of the reflector most sensitive to focal adjustment (or that zone of the reflector approximately embraced within the brackets E, E) with the light source at the focus, projects light to the center of the beam, as a result of which, any change in the position of the light source will produce the minimum change in the beam diameter.

It will be noted that as opposite elements project beams which superimpose, the only portions of the reflector which project light in an upward direction (assuming the light source is approximately at the focus) will be the top thereof, i. e., that portion approximately embraced within the bracket H, and a narrow semicircular band near the center of the reflector immediately below the axis, i. e., that portion approximately embraced within the bracket 1. Therefore, by covering the upper portion H of the reflector so as to dull its reflecting properties by a name, trademark, or the like as at 0, Fig. 2, or deflectin it with a prism and bringing the socket hol ing the bulb in an upward direction from below the reflector vertex at an angle of 15 to to the reflector axis, thus eliminating the reflection from the band, as at P, Fig. 3, at the same time properly positioning the filament at the focus of the reflector, a beam of flattened top will be projected with substantially no loss of light. Also this construction produces the point of maximum intensity near the top of the beam where it is most useful.

With the lamp filament tilted as in Fig. 3, the greatest area of filament will be presented toward the upper portion of the reflector between the angles of 0 and to the reflector axis, or that portion approximately embraced within the bracket J, and the lower portion of the reflector between 60 and 105 to the reflector axis, or that portion approximately embraced within the bracket K. Conversely, less filament area will be presented toward the upper portion of the reflector between 60 and- 105 to the reflector axis, or that portion embraced within the bracket L and the lower portion of the reflector between 0 and 60 to the reflector axis or embraced within the bracket M. Therefore, the portion of the reflector which throws a downward light projects beams of wider spread than the portion which throws upward light, because'the broader projection of the filament is presented to the portions of the reflector which project the downward rays of light. For this reason the complete beam will have less light above the point of maximum intensity than below it. Consequently the reflector is less sensitive to focal adjustment than the parabolic reflector, that is, the lamp filament may be moved a relatively great distance from the focal point of my reflector without projecting light in an upward direction. The upward light produces the glare under service conditions.

approximately uniform brightness In positioning the filament, if the major portion of it is moved slightly below the focal point, a slightly elongated beam cross-sect on will be pro'ected with the brighter portion near the re ector axis, or near the top of the beam, and ta ering off toward the bottom of the beam. I this beam be widened horizontally with a vertically fluted or corru ated front glass, a deep beam approximate y 5 or 6 high, and any width desired, may be projected. By tilting the reflector axlsdownward this beam will have a olnt of h gh intensity near the horizontal or long distance light, tapering olf to illuminate nearby and less important points in front and to the side, thus providing an illuminated roadwa of rom points near the car to distant points.

To illustrate the principles of my invention as applied to a reflecting surface, Figure 6 is shown as an example, in which the generating element is a hyperbola, although it 1s readily understood that the same pr nciples could apply just as well if the generating element were a parabola and ellipse or a combination of these forms. To secure a reflector having the above outlined advantages, a curve has been developed, such that if a narrow strip of reflecting material (a reflector element) be constructed to this curve, and an 1ncandescent filament placed at or near the focal point, the rays of light from the reflector would travel in a fan-shaped beam havinga divergence of 5 from the reflector ax1s. If the beam pattern is to be uniformly bright and made up of superimposed cones, then the most efficient means of obtaining such superimposition is to construct a symmetrical reflector, opposite elements of which are made to project the same types of fan-shaped beams completely overlapping.

A curved strip as above referred to, can be laid out in the form of an element of a hyperbola. The revolution of hyperbola around its true axis would result in a regular hyperbloid and no superimposition of light beams,

would occur. The above desirable superimposition of light beams may be secured by selecting an axis not coincident with the true axis of the reflector and around which the hyperbolic element may be rotated has a generatrix to form this improved reflector surface. Thus, if the hyperbolic element be rotated about an axis Z-Z Figure 6, throu h the focal point p and drawn parallel to t e bisector Pp of the fan-shaped beam, then" the reflector will be a surface of revolution (not a hyperbloid because the axis of revolution Z--Z was not coincident with the true axis po of the hyperbolic element A-0) op posite elements of which will project fanshaped beams completely overlapping.

It will be evident that a reflector of this character will be least sensitive to the movement of 'the filaments away from the focal point becausestarting with the filaments at the focal point and moving it in any direction it can move a maximum distance (because of the overlapping of the beams) without producin a beam of dark center and by thus closing 1n the hyperbolic elements and crossing the fan-shaped beams, a longer focal length reflector can be used for a given collecting angle and the greater the focal length the less the sensitivity.

Thus in Figure 6, a regular hyperbolic reflector, such as A OB, with the light source located at the focal point p, would reflect divergent beams of light as though the light source were located at the conjugate focus point 12 However, in my improved reflector, a symmetrical reflecting surface A()--B, is produced by rotating the hyperbolic elements A'O about the selected axis Z--Z parallel to the line P-p which bisects the light beam from the hyperbolic element AO. Thus, the fan-shaped light beams from the hyperbolic elements AO and OB' superimpose and result in my improved light. It will be noted that in an ordinary hyperbolic reflector, the conjugate focus is a single point p while in my improved reflector, the conjugate foci fall in a series of points 17, p describing a circle.

The inclusion of vertically or nearly vertically flattened sections to spread the beam laterally, as shown in Fig. 4, will not in any way affect the insensitiveness of my improved reflector to focal adjustment or in other words its set-focus characteristic. These flattened sections, if provided, will project overlapping flattened beams, and the reflector will project the desired beam pattern without the aid of a modifying lens.

Having now described my invention, what I claim as new tl18IBl11' and desire to secure by Letters Patent is as follows:

1. An improved reflecting surface formed by the revolution of a hyperbolic element around an axis, said axis passing through the focal point and parallel to a bisector of the fan-shaped beam projected from said hyperbolic element, thus making the opposite fanshaped beams overlap and form a round uniforml bright beam.

2. improved reflector of which each element is hyperbolic and projects from center to extremity, a diverging beam equal to the extreme width of the reflector beam pattern, said element being rotated about an axis passing through the focus and making an angle with the hyperbola axis so that beams from said elements located diametrically opposite with respect to said axis of rotation, completely overlap and eliminate streaks from manufacturing irregularities and filament images.

tersects the true hyperbolic axis at an angle, the opposite hy erbolic elements project overlappin fan-s a ed beams of any desired spread, an an incan escent lamp placed with 5 its axis at an angle to the reflector axis, the base downward, so that the projected area of the filament is greatest toward that part of the reflector which pro'ects downward light, and the least projecte area of the filament 19 toward that part of the reflector which pro- 'ects upward light, and locating the lamp ase in such a position that it intersects the light rays whic would otherwise be projected upwardly at the greatest angle to the 5 reflector axis.

4. An im roved reflector which is a surface of revo ution formed by the rotation of a hyperbolic element about an axis passing through the focus and parallel to a median 2n line bisecting the normal fan-shaped beam projected from said by rbolic element so that the rays of li ht flibm said reflecting surface are able to c iange their direction the maximum amount without forming a dark centered beam pattern for a. given displace ment of the light source along the axis from y the focal point.

This specification signed this twenty fifth day of November, 1925. v :0 WILLIAM F. LITTLE. x

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