Patent GB-301942-A (GB)
Title: Projecting reflector for light and other radiant energy
IPC: F21V7/04
Filed: 1927-08-08
Abstract: 301,942. Wood, W. G. Aug. 8, 1927. Reflectors.-In a heat reflector, vertical sections of the lower portion of the reflector are in the form of ellipses, this lower portion being built up of a series of downwardly diminishing ellipses lying in planes converging to a remote horizontal transverse line. The upper portion of the reflector may be symmetrical with the lower portion, or it may be in the form of a hemiellipsoid. The surface of the reflector may be made smooth by using an infinite number of downwardly diminishing ellipses, or it may be formed of a limited number of sections of finite width. In the form shown in Fig. 1, the vertical section ellipses have common proximate foci F1, remote foci F<1>, - - F<1>4 lying in a vertical plane on a line which may be straight ur curved, such as the arc of a circle with centre at F<2>1, major axes A1, A<1>1, - - A4A<1>4 of equal length, and proximate vertices A, - - A4, and remote vertices A<1>1 - - A<1>4 lying on arcs of a parabola, ellipse, or hyperbola. T1 - - T4 and T<1>1 - - T<1>4 indicate respectively the proximate and remote vertices of the downwardly diminish. ing ellipses converging to a remote horizontal transverse line F<2>1 F<2>2 intersecting the longi. tudinal axis of the reflector at the remote focus F<2>1. The latter may be at infinity, or in front or behind the common proximate foci F1 in which cases the proximate vertices T, - - T4 lie respectively on parabolic, elliptical or hyperbolic curves, each having foci coinciding with the foci F1 F<2>1. In each case the remote vertices T<1>1, - - T<1>4 lie on the arc of an hyperbola having foci at F, F<2>1. The reflector is formed from the external limiting surface of these ellipses, and rays from a source at the common proximate, foci F, will cross at the remote foci F<1>1 - - F<1>4 to diverge laterally at a wide angle through a narrow aperture cut in the reflector at or adjacent to the remote foci, and will then converge vertically on to the horizontal transverse line F<2>1, F<2>2. The rejector may also be formed from the internal limiting surface generated by revolving conic sections about their longitudinal axes, and then revolving the quadric surfaces of revolution so formed about a common focus as centre, the axes moving in a plane so as to maintain the remote foci on a transverse line in that plane, the surfaces all containing a fixed point outside but adjacent to that plane. In the form shown in Figs. 3 and 4, F, is the common foci, T<1>4 is the common external point, and F<1>1 T<1>4 is a circular arc with centre at F<2>1. Straight lines from the remote foci F<2>2 passing through points such as F<1>1, F\ on the circular arc F<1>1 T<1>4 intersect the ellipsoid V2 N, V<1>2 M1 at points such as T<2>2 T<2>3. By taking an infinite number of such lines, the points of intersection form a surface which is shown in a median horizontal section as an ellipse V1 O1 V6 P1 in Fig. 3, and in medial vertical section as T1 T<1>4 V6 T<2>4 V1 in Fig. 4. The quadric surfaces of revolution will be paraboloids, ellipsoids or hyperboloids, according as the remote foci F<2>2 is at infinity, or inside or outside the surface. The proximate vertices lie on the curve V1V2 V4 V6 V7 V1, and the remote vertices on the hyperbolic arc V<1>1 T<4>2. The hyperboloidal surface may be used when it is desired to reflect some of the heat rearwardly and sideways. For this purpose the reflector may be cut away along the line T<2>2 T<1> to allow heat to be reflected from the arc T<2>7 T<1>4. The reflector may also be formed from the internal limiting surface generated by intersecting the surfaces of the quadric surfaces of revolution by a series of right circular cones, the vertices of which coincide with the remote foci, one element of each cone passing through a fixed point in the plane containing the axis of the cone and the fixed proximate foci, and ter. minating at a point which is common to the quadric surface of revolution and which lies on an ellipse having foci at the fixed proximate foci and the said fixed point. In Fig. 3, F<2>2 F<2>1 is the axis upon which lie the coincident positions of the remote foci and the vertices of the cones, F<1>1 is the fixed point, and V, O1 V6 P, is the said ellipse. Specification 239,782, [Class 75 (ii), Lamp chimneys &c.], is referred to.