Patent GB-648271-A (GB)
Title: Improvements relating to the projection of light rays
IPC: F21S8/00
Filed: 1947-08-18
Abstract: 648,271. Lighting system; electric lamp bulbs. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 18, 1947, No. 22889. Convention date, March 27, 1944. [Classes 39 (ii) and 75(iv)] [Also in Group XX] A device for the projection of radiations from a source emitting radiations falling into two predetermined wavelength groups A and B, comprises two similar confocal concave surfaces, one of which has been treated to reflect the radiations of group A and transmit the radiations of group B whereas the other has been treated to transmit the radiations of group A and reflect the radiations of group B, said surfaces having their concave faces directed towards each other so as to form an enclosure within which the source of radiations may be located at the common focus. The device shown in Fig. 1 comprises two confocal parabolic members 2, 4 as of glass having a light source F at their common focus. The member 2 transmits the radiation emitted from the source F and which falls in the wavelength group B and reflects the radiations of group A, whereas the radiations of groups A and B are respectively transmitted and reflected by the member 4. The group B radiations transmitted by member 2 and the group A radiations transmitted by the member 4 are directed in opposite directions by metal or silvered glass reflectors 3, 1 respectively, these reflectors being parabolic and having the same focus and axis as the members 2, 4. In the respective paths of the radiations A and B may be placed filters to vary the intensity of the beams and/or reflectors, inclined at the same angle to the vertical, whereby the radiations are caused to fall onto the same surface. Hence, if source F, which may be an incandescent lamp for which members 2, 4 form a bulb, emits only visible radiations, the radiations of group B may comprise light of a colour complementary to that of the group A radiations so that the surface onto which the radiations fall appears white. If the group A radiations comprise ultar-violet light, while the group B radiations comprise visible light, the radiations of group A may be used to excite fluorescent materials in the path thereof and the light emitted thereby can be combined with the visible radiations of group B to illuminate a surface. The device may also comprise two confocal parabolic members 23, 24, one of which is rotatable about an axis Z-Z, Fig. 6, so that the radiations of groups A and B may be reflected in the same or in opposite directions and a lamp 25 the spherical envelope of which is such that the upper half thereof transmits group A radiations and reflects group B radiations while the lower half respectively reflects and transmits group A and group B radiations. The device may also form the headlamp of a car and may be used for street lighting. The Specification as open to inspection under Sect. 91 also describes a device comprising an ellipsoidal envelope having an incandescent source at one focus thereof. The visible radiations emitted by the source are transmitted by the envelope and the infra-red radiation emitted is reflected onto a tungsten bead positioned at the other focus of the envelope. This bead becomes heated and the infra-red radiations emitted thereby are returned to the original source. In another form, two incandescent sources are positioned, one at each focus of the envelope. This subject-matter does not appear in the Specification as accepted.