Illumination – Light source and modifier – Including reflector
Patent
1984-07-31
1986-01-14
Argenbright, Tony M.
Illumination
Light source and modifier
Including reflector
362346, 362347, F21V 702
Patent
active
045648921
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatus for producing two mutually divergent light beams from a single light source. Such apparatus is useful in dental and other medical lamps where the two beams are re-directed to a common illumination area by mirrors in the paths of the two beams, so as to achieve the effect of illumination from spaced light sources, for the purpose of producing relatively shadow-free illumination.
Apparatus has been proposed for producing two oppositely-directed light beams in which light from a source is collected by a concave reflector to produce a convergant beam. The beam is incident on a pair of mirrors oriented at about 45.degree. to the beam axis and on respective sides of the axis. The two mirrors split the beam into a pair of beams which are oppositely-directed and are perpendicular to the first beam. In a lamp unit incorporating the known apparatus, each beam is re-reflected and focused so that the two beams combine at a plane to form a single patch of light. The illumination provided at the plane is substantially shadow-free, because the two beams arrive at the plane from different directions. Thus, in many situations when an object blocks a first of the beams, the shadow of the first beam is illuminated by the second beam. By using light stops in the path of each beam to limit the width of the beam; and by arranging that the image of the stops is at the plane of the patch, the apparatus provides a patch of light which cuts off abruptly.
The object of the present invention is to provide an improved apparatus which is more compact and requires fewer reflections, and thereby reduces the light losses which are inevitable at each reflection.
The present invention provides apparatus for producing two mutually divergent light beams from a single light source, comprising two concave reflector portions each of which widens away from a respective beam-emission axis from a first end to a second end, at which second end is the beam-emitting aperture of the reflector portion, the two reflector portions confronting and overlapping each other at their first ends and having their beam-emission axes mutually divergent, whereby a light source disposed between the overlapping regions of the reflector portions produces the two mutually divergent beams.
The two reflector portions may be strips with simple curvature such as to produce the widening away from the beam-emission axes. However, it is preferred to employ sectorial portions having compound curvature. For example, the two portions may be halves of a complete concave reflector such as a parabolic or ellipsoidal reflector. Alternatively the two portions may be cut down (notionally) from such halves. Such notional cutting down is not restricted to reducing the angle subtended at the beam-emission axis. For example, any part of a half reflector which makes little useful contribution to the emergent beam can be cut away without adverse effect and the perimeter of the sectorial portion may be of largely arbitrary shape. Those parts of the reflector surfaces which reflect light which is subsequently interrupted by a stop may therefore be cut away. Parts of the reflector portions may also be cut away specifically to allow introduction of the light source.
Apparatus according to the invention produces two mutually divergent light beams without using mirrors additional to the concave reflectors and by using reflectors which may be smaller than the reflector used in the known apparatus described above. Smaller reflectors may be more easily made. Since each reflector is only a sector, it can be made by pressing in a mould. Small reflectors are cheaper to produce by pressing than by the process used for making large reflectors of sagging a heated glass plate into a concave pattern. Small reflectors may be more accurately coated since the coating is applied on to a relatively open sector instead of into a deep, cup-like reflector. The optical path of the present apparatus is more compact than that of the known apparatus because the limb of the path
REFERENCES:
patent: 4409646 (1983-10-01), Baliozian
patent: 4441141 (1984-04-01), Lo
Argenbright Tony M.
J & D Oram Limited
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