Apparatus for projecting electromagnetic radiation with a...

Illumination – Light fiber – rod – or pipe – Illuminating or display apparatus

Reexamination Certificate

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Details

C362S298000, C362S301000, C362S346000

Reexamination Certificate

active

06238077

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to apparatus or systems that project electromagnetic radiation over a predetermined field of view with a tailored intensity distribution. In a lighting system, for example, an embodiment of the invention provides desirable intensity over the desired area of illumination.
BACKGROUND
Devices or optical systems of this particular kind are commonly used to project electromagnetic radiation, especially visible light. Such a device, for example, may illuminate a desired area or footprint, to allow people to see freely or observe specific objects within the desired area. Other illumination devices project radiation over a hemisphere, i.e., 2&pgr; steradians, for a variety of applications. Examples of these later applications include use as a warning light on an emergency vehicle's light bar or as an aircraft warning light. In each different application, the projected light has a predetermined intensity distribution to facilitate the intended or expected use of the light. To illuminate a surface, such as a picture displayed on a wall, a desktop or a floor or sidewalk, the intensity distribution may need at least some minimum intensity over the entire desired surface area. In such applications, producing the requisite intensity on the edges of the area has often required excess illumination in the center of the area. Other applications require a uniform intensity profile over a hemispherical field of view.
One type of apparatus intended to provide uniformity with respect to angle is a translusive diffuser, which includes a sheet of translusive material disposed over a light source. Light from the light source passes through the translusive sheet and is diffused into the surrounding space. Suitable translusive materials include opal glass, acrylics, and Teflon. The translusive sheet sometimes is covered by a transparent protective dome or the sheet, itself, sometimes is formed into a dome shape. Although generally effective in projecting light substantially uniformly, translusive diffusers are considered to be unduly inefficient, projecting only about 20% to 25% of the available light when configured as a hemispherical light distributor.
Another type of apparatus of this kind is a beam redirector, which includes an optical device having a special refractive or reflective surface for redirecting light from a light source such as a laser into a hemisphere. Although such beam redirectors are relatively inexpensive to manufacture, they typically require a critical alignment between the light source and the optical device, and they typically require the use of a light source that provides a light beam having a known, stable intensity distribution. Moreover, the projected light often has a spatial intensity distribution that varies excessively.
Lighting systems for interior rooms or for streets or sidewalks and the like have used a wide variety of different types of diffusing mechanisms. Many lights have a translucent globe around the source. Other lighting devices use reflectors with diffusers over the reflectors and/or baffles at the opening or within the reflectors. These various mechanisms help to distribute radiation in some desired patterns, but only to a limited extent. Also, such mechanisms tend to reduce the efficiency of the illumination of radiation from the lighting system. Many techniques for distributing the energy also tend to be unduly complex, increasing manufacturing costs and/or resulting in systems that are easily damaged.
It should, therefore, be appreciated that there is a need for an apparatus that projects electromagnetic radiation over a predetermined field of illumination with a tailored spatial intensity distribution, wherein the radiation is projected with greater efficiency and with less dependence on a critical alignment of optical components. In many cases, the tailoring needed relates to a uniform intensity distribution, over a surface area or over some range of angles defining the field of illumination. The present invention fulfills these needs.
SUMMARY OF THE INVENTION
The present invention utilizes the principles of constructive occlusion, with selection of the optical parameters of the constructive occlusion system, to satisfy the performance demands of the particular application. Constructive occlusion utilizes a mask sized and positioned to occlude a substantial portion of an active optical area, such as an aperture of a diffusely reflective cavity in a base or a reflective image of such a cavity onto a base, in such a manner as to provide the desired performance characteristic with a high degree of efficiency. The inventive optical systems also include a reflective baffle for redirecting certain portions of the radiation diffusely reflected between the base and the mask outward into peripheral regions of the field of illumination of the system, for example toward the horizon of the device or to areas approaching the periphery of the intended illumination footprint. As such, the baffle serves as a “kicker” to kick additional radiation to specific sections of the field of illumination and increase the intensity within those sections.
The preferred embodiments encompass a number of different structures for the baffle. In one example, where the cavity is formed in the base, the baffle takes the form of a cone projecting from the mask toward the cavity, and possibly into the cavity. Other examples of the baffle include members extending toward the cavity but having right-angled sections or walls extending radially outward from the system axis. These baffle walls divide the cavity and/or the space between the mask and the aperture into sections, for example, into quadrants. Other examples of the baffle include elements located entirely within the cavity.
One preferred embodiment of the baffle comprises a central planar surface about the axis and an annular bevel, at an angle to the planar surface. Both the planar surface and the surface of the annular bevel are diffusely reflective with respect to visible light.
The source can include an optical fiber that terminates within the cavity, coaxial with the aperture, or it can include a lamp located on the mask's underside, adjacent to the baffle. In another embodiment, the mask includes another reflective cavity having an opening facing the cavity in the base. The source comprises a lamp or the like located within the cavity in the mask.
Another aspect of the present invention is embodied in an apparatus that projects electromagnetic radiation over a predetermined spherical sector, with a tailored spatial intensity distribution, wherein the radiation is projected with improved efficiency and with less dependence on a critical alignment of optical components. The apparatus includes a base that faces the spherical sector to be illuminated, a mask that is spaced a predetermined distance from the base, and a source that emits electromagnetic radiation into the space between the base and the mask. In addition, a cavity and aperture are formed in one of the base and mask, facing the other of the base and the mask. The base and the mask are formed of a material having an outer surface with a significant diffuse reflective characteristic, and they are configured to redirect the emitted radiation with the tailored spatial intensity distribution (e.g., a uniform distribution) over the predetermined spherical sector.
In a more detailed aspect of the invention, the cavity is formed in the base, and the base further includes a flat, ring-shaped shoulder that encircles the cavity's aperture. The apparatus further includes a baffle disposed between the base cavity and the mask and may be integral with, or otherwise secured to, the mask. For embodiments in which electromagnetic radiation is to be projected with an intensity distribution that is circumferentially symmetrical, the base's cavity and shoulder, the mask, and the baffle all are circumferentially symmetrical and are arranged in a coaxial relationship. In addition, the aperture is substantially

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