Illumination – Light source and modifier – Including reflector
Reexamination Certificate
1998-04-03
2001-05-08
O'Shea, Sandra (Department: 2875)
Illumination
Light source and modifier
Including reflector
C362S297000, C362S301000, C362S346000
Reexamination Certificate
active
06227684
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a luminaire comprising:
a concave reflector with a plane of symmetry and an optical axis having an optical center lying in the plane;
a light emission window tangent to the reflector and transverse to the plane of symmetry;
holder for accommodating an electric lamp transversely to the plane of symmetry, with an elongate light source of the lamp in the optical center and;
a light-reflecting screen extending along the optical axis, transverse to the plane of symmetry; and reaching up to in the light emission window,
the reflector comprises several plane facets which in their widths w are bounded by first, mutually substantially parallel, substantially flat planes perpendicular to the plane of symmetry, and which in addition in their lengths l are bounded by second substantially flat planes which arrange the facets into rows which extend along the plane of symmetry.
Such a luminaire is known from U.S. Pat. No. 5,544,030.
The known luminaire is not only symmetrical in the plane of symmetry, but substantially also in a plane perpendicular thereto and passing through the means for accommodating a lamp. The luminaire comprises a large number of mutually parallel second flat planes which bound the facets. The reflector is tangent to the light emission window around the optical axis, and the optical axis is perpendicular to the window. The luminaire is capable of concentrating light generated by an accommodated lamp into a substantially symmetrical light beam.
The luminaire may be positioned with its optical axis pointing obliquely downward. A screen is provided in the space defined by the reflector above the optical axis. The screen thus intercepts all light beams originating directly from the lamp which would be radiated in upward directions if the screen were absent.
The known luminaire is accordingly suitable for use inter alia in the illumination of grounds, for example sports grounds, because the luminaire counteracts the radiation of stray light, i.e. light not directed at the grounds to be illuminated. Irregularities in a transparent plate closing off the light emission window, however, or pollution on this late may nevertheless give rise to unpleasant stray light which is directed horizontally or upwards, as may light reflected by the plate towards the reflector.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a luminaire which yields a comparatively wide light beam transverse to the plane of symmetry, while the radiation of unpleasant stray light is effectively counteracted.
According to the invention, the first substantially flat planes enclose an acute angle with the light emission window, and the screen extends from the reflector up to the light emission window.
The luminaire can be used for illuminating a horizontal surface with its light emission window in horizontal position, facing downwards, owing to its geometry with the reflector sloping down towards the light emission window. If the light emission window is closed off with a transparent plate, this plate can no longer cause any stray light in upward direction. Light reflected by the plate towards the reflector cannot do this either. The luminaire may even be used in the open condition, without a closing plate, if there is no risk of pollution by the environment.
The luminaire provides an asymmetrical beam, a beam which is narrow above the optical axis and wider below it in the above-mentioned position of the luminaire, and which may be comparatively wide transversely to the plane of symmetry, for example 2×35°. Seen from the lamp, the beam then has a light intensity at angles of 35° to the left and right of its center which is half that in the center. Nevertheless, the luminaire is compact in relation to the lamp to be accommodated. Its geometry avoids double reflections in the luminaire to a high degree and leads to a high efficiency. In spite of the comparatively wide beam to be realized, which renders possible the illumination of a comparatively large ground surface area, the luminaire is capable of realizing light beams with maximum intensities of 1000 up to 1600 cd/klm. A ground surface can be illuminated up to a comparatively long distance from the luminaire as a result in a homogeneous and efficient manner. Added to this, the screen provides a sharply defined cut-off angle, for example of approximately 15-25°, for example 25° to the horizontal plane. Stray light is avoided to a high degree within this cut-off angle, and is entirely absent above the horizontal plane.
The first flat planes may enclose an angle of, for example, 15-30°, for example 25° with the light emission window.
The reflector may reach up to in the light emission window with rows of facets on either side of the plane of symmetry. It is favorable, however, when side panels extend up to the screen on either side of the plane of symmetry, which panels extend to in the light emission window and bound facets of remote rows, i.e. rows lying farthest removed from the plane of symmetry. A gradual boundary of the light beam and a gradual light/dark transition of the illuminated field is obtained thereby.
The screen and the side panels may be, for example, diffusely reflecting. This leads to a lower luminance of said parts, and accordingly less glare when these parts are viewed. A portion of the screen adjoining the light emission window may have a white coating, for example be painted white. If a transparent plate closes off the light emission window, this paint can then prevent reflections on this plate and subsequently on the screen from causing local brightness differences in the illuminated field.
The side panels may be, for example, perpendicular to the light emission a window. They then provide a comparatively small spread to the light incident thereon and originating directly from the lamp. It is useful, however, for avoiding double reflections, for example from side panel to side panel, and for counteracting glare, when the side panels approach one another in a direction towards the screen. They may then each enclose an angle of, for example, 75 to 80° with the light emission window. It is also possible for the side panels to intersect the light emission window parallel to one another or to approach the reflector at an angle to one another which amounts to several degrees, for example
4
to
10
, for example 6°.
A favorable light distribution in the beam is obtained in particular when the first flat planes have points of intersection with the reflector in the plane of symmetry which lie substantially on a parabola whose focus is the optical center. It is in addition favorable when the reflector has facets with a greater width w at a side of the optical axis reflected by the facets.
BRIEF DESCRIPTION OF THE DRAWINGS
To counteract reflections on the screen of light originating from the reflector, it is favorable when the screen and the optical axis diverge by an angle of a few degrees, for example 5°, towards the light emission window. In a special embodiment of this, the first planes are substantially parallel to the screen. It is achieved thereby that the maximum of the light beams formed will lie somewhat higher, for example by 2°, and the luminaire thus radiates farther.
The evenness of the illumination of an irradiated field may be enhanced in that the facet lying closest to the screen in the plane of symmetry is tilted inwards into the parabola along this screen. Light reflected by this facet is then added to the beam again at the side of the optical axis other than that where the screen is present.
For certain applications, for example if also a field portion immediately below the lamp is to be illuminated, the facet tangent to the light emission window in the plane of symmetry may be tilted outwards from the parabola along the light emission window so that it has come to be, for example, perpendicular to the light emission window.
It is favorable for the creation of a comparatively wide beam transverse to the plane of symmetry when the reflector has no mo
Entrop Jean P.
Wijbenga Hendrik
O'Shea Sandra
Spain Norman N.
U.S. Philips Corporation
Zeade Bertrand
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