EP0005080B1

EP0005080B1 - Spotlight lantern projection system

Info

Publication number: EP0005080B1
Application number: EP19790300700
Authority: EP
Inventors: Martin Warwick Moore; Roderick Alexander Mckenzie
Original assignee: Rank Organization Ltd
Current assignee: Rank Organization Ltd
Priority date: 1978-04-26
Filing date: 1979-04-25
Publication date: 1982-02-24
Also published as: GB2019999B; GB2019999A; EP0005080A1; DE2962174D1

Description

This invention relates to a light projection system for a spotlight lantern.
A spotlight lantern is required to produce a well-defined beam of light having an even distribution of light through its cross-section. For reasons of efficiency, it is necessary to employ a light source, e.g. an electric filament, in conjunction with one or more reflectors. This combination is referred to herein as a light projection system. The light projection system concentrates light through a gate, shaping pattern or iris (collectively referred to as a gate subsequently), and then through an optical objective, in order to produce the required beam.
The object in designing the light projection system is uniformly to fill the gate, pattern or iris with light so that as much light as possible is concentrated by the objective to produce the required uniform, well-defined beam having a minimum of light spill at its edges.
From the prior art, various reflectors and combinations of reflectors are known. Thus, European 220/240 volts lanterns conventionally employ a grid filament mounted perpendicular or approximately perpendicular to the optical axis of the lantern. In conjunction with such filaments, it has been proposed to use rear reflectors defined by various part surfaces of revolution, in particular conic sections such as spherical sactions ellipsoidal sections and parabolic sections. It is also known to combine one such rear reflector with a partial frontal reflector likewise conforming to a surface of revolution, such as a spherical rear reflector with an ellipsoidal frontal reflector or an ellipsoidal rear reflector with a spherical, ellipsoidal or hyperbolic frontal reflector. More complicated reflectors have also been proposed, including reflectors defined by curves representing cartographic projections and reflectors based on surfaces of revolution modified by localised flattening, the aim being to improve efficiency and light distribution. The inclusion of a lens system between the lamp and the gate can also improve performance, but in spite of these refinements there is substantial waste light and/or non-uniform light distribution at the gate.
In the United States, the use of a 110/120 volts mains electric supply has made possible the development of spotlight lanterns incorporating a light projection system based on a linear spirally wound coil filament mounted along the optical axis. With this type of filament, using a parabolic rear reflector, the radiated light can be collected and projected forwardly so as just to fill the gate with uniform distribution. This system thus shows significantly improved efficiency and performance compared with most European light projection systems. However, it has so far proved impossible to produce satisfactory short and reliable spirally wound coil filament lamps to operate at 220/240 volts. Existing 220/240 volts linear lamps have fragile filaments which do not remain linear in use. Furthermore, the length of the filament results in poor light distribution and undesirably large lanterns.
Finally, U.S. Patent No. 3,930,149 discloses a lighting device of adjustable intensity and intended for use in dentistry, wherein a lamp has a coil filament backed by an ellipsoidal reflector and a light gate which is just filled with light in the position of maximum intensity and is axially movable to reduce intensity.
The object of the present invention is to provide an improved light projection system which is suitable for the European 220/240 volts mains supply which avoids substantial waste light and non-uniform light distribution at the gate.
According to the invention, there is provided a light projection system for a spotlight lantern, comprising a filament lamp and a concave reflecting means from which filament radiated light is reflected through a gate to an optical objective in order to form the spotlight beam, the lamp having a flat elongate grid filament disposed axially on the axis of the reflecting means, characterised in that said reflecting means has facets each of which produces a patch of light which just fills the gate.
The reflecting means preferably comprises a rear reflector in the form of a partial surface of revolution defined by a large plurality of facets. These facets may cover the reflector regularly or irregularly.
A partial frontal reflector may be employed in addition. This may also be facetted, but alternatively may be spherical or hyperbolic. A spherical rear reflector may be employed when the frontal reflector is facetted.
With any of these reflector arrangements in accordance with the invention, each reflector facet in use produces a patch of light which just fills the gate.
An arrangement of light projection system in accordance with the invention will now be described with reference to the accompanying drawings, in which:-
Figures 1 to 3 respectively show three differing reflector arrangements which may be employed in conjunction with an axial grid filament, and
Figures 4 and 5 show constructional details of a facetted rear reflector.
The arrangement shown in Figure 1 comprises a 220/240 volt lamp 10 having a flat elongate grid filament 11. Such a lamp has a conventional cylindrical envelope, but in accordance with the invention the grid filament 11 extends axially, lying along the axis of the envelope, which is collinear with the optical axis 0 of the lantern. The lamp 10 is mounted longitudinally on the axis of a cup-shaped rear reflector 12, which axis is also collinear with the optical axis 0. The surface of the reflector 12 generally conforms to a conic section such as a paraboloid or an ellipsoid. An aperture is provided at the centre of the rear reflector 12 to accommodate the lamp 10 extending axially therethrough, so that the grid filament 11 is disposed along the axis of revolution of the reflector.
The reflector is more exactly defined by a large plurality of small facets or flats which subdivide the reflector into annular zones. One example of rear reflector 12, shown in Figures 4 and 5, has about eleven annular zones 20 defined by the facets 21, each zone 20 having about thirty six facets 21 extending around the reflector to define a regular polygon having thirty six sides. In such a case the reflector 12 is said to be regularly facetted. The zones 20 are of approximately equal width w measured along a generator 22 of the reflector 12, and therefore the width of said zones measured by projection thereof on to the axis 0, increases from the centre of the reflector outwardly to the zone of greatest diameter. Figure 5 is also marked to show the respective angles made by the facets 21 of successive zones 20 with the intersecting zonal planes 23 normal to the axis O. With regular facetting, the facets 21 are of increasing width x around successive zones 20 with increasing diameter of the reflector 12. It may sometimes be preferable to vary the widths x of the facets 21 within each of some or all of the zones 20 depending on whether said facets are illuminated by the edge of the grid filament 11 or by the face thereof. In such a case the reflector 12 is said to be irregularly facetted.
The above-described arrangement can employ a partial frontal reflector in addition to the rear reflector, as shown in Figures 2 and 3. In Figure 2, such frontal reflector 13 is defined by an annular portion of a regular spherical or hyperbolic section, facing rearwardly to reflect light from the filament 11 on to the rear reflector 12, from which the light, together with that directly incident on the rear reflector 12 from the filament 11, is reflected forwardly through the axial zone defined by the inner diameter of the frontal reflector 13.
The modification shown in Figure 3 employs a facetted frontal reflector 14. In this case, however, the frontal reflector 14 is employed to reflect light from the filament 11 in the forward direction. When the facetted frontal reflector 14 is employed, a rear reflector 12 of regular spherical form may be used instead of a facetted rear reflector.
In all cases, the grid filament 11 is disposed axially, being contained in a plane also containing the axis O of the reflector or reflectors (12, 13, 14). However, the location of the filament 11 along the axis 0 varies with the reflector arrangement employed. Generally, the filament 11 is situated deeper into the cup-shaped form of the rear reflector 12 when a frontal reflector 13 or 14 is omitted, and furthest outward from the bottom of the cup when a frontal reflector 13 is employed which reflects light rearwardly. In all instances, however, the filament is contained wholly within the cup, as shown in the drawings.
In all embodiments (see Figures 1 to 3), the light projection system is arranged so that each facet 21 reflects from the grid filament 11 a path of light which just fills a beam-confining aperture means 15 located between the light projection system and an optical objective 16, which aperture means 15 is constituted by a gate. More especially, instead of a concave reflector having the usual continuously curved reflecting surface, which reflector in accordance with conventional practice could be arranged to produce an image of the filament at the gate, a modified facetted reflector is employed with facets dimensioned each to produce a patch of light which just fills the gate. In this way it is ensured that a spotlight lantern, in which the light projection system together with the aperture means 15 and the objective 16 are incorporated, will produce a well-defined beam with minimum light spill at the edges, with uniform distribution of light through the section of the beam, and also with minimum waste of light, thus ensuring high efficiency.
It should be appreciated that the above described arrangements are by way of example only and may be modified in various ways within the scope of the invention, especially in respect of the arrangements of reflector or reflectors.

Claims

1. A light projection system for a spotlight lantern, comprising a filament lamp (10) and a concave reflecting means (12 or 13 or 14) from which filament radiated light is reflected through a gate (15) to an optical objective (16) in order to form the spotlight beam, the lamp (10) having a flat elongate grid filament (11) disposed axially on the axis of the reflecting means (12 or 13 or 14), characterised in that said reflecting means has facets (e.g. 21) each of which produces a patch of light which just fills the gate (15).

2. A system according to claim 1, characterised in that the reflecting means comprises a rear reflector (12) in the form of a partial surface of revolution defined by a large plurality of facets (21).

3. A system according to claim 2, characterised in that the grid filament (11) is wholly contained within the cup defined by the rear reflector (12).

4. A system according to claim 2 or claim 3, characterised by a regu!arly facetted rear reflector (12).

5. A system according to claim 2 or claim 3, characterised by an irregularly facetted rear reflector (12).

6. A system according to any of claims 1 to 5, characterised in that the reflecting means includes a partial frontal reflector (13 or 14).

7. A system according to claim 1, characterised in that the reflecting means comprises a rear reflector (12) and a partial frontal reflector (13 or 14), at least one of which is facetted.

8. A system according to claim 7, characterised by a facetted partial frontal reflector (14).

9. A system according to claim 8, characterised by a spherical rear reflector (12).

10. A system according to claim 7, characterised by a facetted rear reflector (12).

11. A system according to claim 10, characterised by a spherical partial frontal reflector (13).

12. A system according to claim 10, characterised by a hyperbolic partial frontal reflector (13).