Illumination – Revolving
Reexamination Certificate
2000-04-14
2003-06-10
Cariaso, Alan (Department: 2875)
Illumination
Revolving
C362S327000, C362S330000, C362S346000
Reexamination Certificate
active
06575584
ABSTRACT:
The present invention is related to an illumination device. The present invention is also related to several applications of the use of reflective micro-prisms into specific embodiments.
Illumination devices are known in the art. Illumination devices are based on a light propagation through a plastic plate by total internal reflection (generally referred to as TIR) wherein the light may be extracted from the plate by various systems;
a system based on diffraction gratings;
a system based on micro-diffuser;
a system based on micro-prisms.
The first kind generates a wavelength dependant illumination, which is unwanted for display applications since screen lighting has to be white.
The second kind generates diffuse light without precise control of divergence, which results in an inefficient illumination device.
The third kind is related to the field of the present invention.
More particularly, several documents have described more specific embodiments.
For example, U.S. Pat. No. 5,833,517 is describing a gradation pattern formed by sandblasting of a surface to allow outgoing of light by scattering.
U.S. Pat. No. 5,649,754 is describing a similar plate with outgoing of light based on irregular reflectors regions resulting in scattering of the light out of the plate.
U.S. Pat. No. 5,833,517 and U.S. Pat. No. 5,649,754 are using scattering effects which are random dependant and always generate a high divergence of the output beam.
U.S. Pat. No. 5,485,291, U.S. Pat. No. 5,485,354 and U.S. Pat. No. 5,664,862 are describing a guiding plate wherein light is extracted with micro-prisms. Those prisms are etched at the back-side of the plate. An input light beam is refracted through the prisms and a reflective flat surface is used to reflect back the light through the plate thickness and the front surface, producing an output light beam. Such back travelling of the light compromises light transmission inside the plate and is not efficient to control divergence properties of the output light beam.
U.S. Pat. No. 5,128,842 is describing a thin micro-prism plate wherein each prism formed on the underneath surface, is coated with a fully reflective coating. When light is hitting a prism, it is reflected out of the plate and a high intensity spot of light is generated out of the device. But when light is hitting an interface between 2 prisms, it is reflected under TIR conditions inside the plate and no spot-light is extracted from that location. Light distribution of the output light beam cannot be considered as continuous, especially when distance between prisms is large. In such a case one have a discrete light distribution. No smooth illumination is produced. One may also have divergence of the output light beam. A disadvantage of such plate is coming from a metallic coating at the bottom of the plate. When light, particularly coherent light is hitting the coating, it is reflected and diffraction may occurred at the prisms edges resulting in a disturbed output light beam. A contribution of diffracted light in the output light beam, generates a scattering effect of the light, which is particularly disastrous for a fan-out generator. Output light divergence and intensity distribution are totally out of control.
SUMMARY OF THE INVENTION
It is one of the various objects of the present invention to provide an improved illumination device.
We have now found that the scattering and the divergence effects in the output light beam are significantly reduced when micro-prisms are located inside the illumination device.
It is another object of the present invention to develop a device that allows a uniform illumination for compact and low-cost characteristics.
It is another object of the present invention to develop a low-cost plate generating a fan-out of beams that allows a discrete distribution of the output light beam by beam splitting inside the plate.
According to the present invention, there is provided an illumination device comprising a plate provided for guiding light there through, having an input for receiving an input light beam to be injected into said plate and an array of N micro-prisms provided for receiving the input light beam and producing an output light beam from said input light beam characterised in that the array of N micro-prisms are located inside the plate.
Advantageously, when the micro-prisms are located inside the plate, one has a medium of homogenous refractive index surrounding the micro-prisms.
The input light beam to be injected into the plate of this invention, may be provided from a light source such as an optical fibre or an extended light source such as a tube lamp, a light bulb or a LED (Light Emitting Diode) in order to obtain an uniform output light beam intensity.
The input light beam may also be provided by a light source with low divergence and small section, in order to generate an output fan-out of beams. For example the light source may be an optical fibre with a collimating lens, a laser diode with a collimating lens or a gas laser beam.
Preferably the input light beam is injected into the plate by one edge.
In an illumination device according to the invention, the plate is provided for guiding light. It may be made, for example, of glass, plastic material, rubber material or composite material.
The input light beam is propagating inside the plate by transmission and reflection.
An array of micro-prisms according to the invention is provided for receiving the input light beam and producing an output light beam. Such prisms have an inclined reflecting surface.
When light is hitting a micro-prism on its inclined reflecting surface with an incident angle inferior to 90 degree, it is partly reflected onto the micro-prism. Light may also be transmitted inside the plate by total reflection on the plate sides.
Preferably, when light is hitting a micro-prism on its inclined reflective surface, it is partly reflected and partly transmitted through the prism to the next micro-prism.
Advantageously such illumination device provides a higher degree of control of the illumination outgoing the plate. In particular, uniformity and divergence of the output light beam may be optimised.
Another advantage is that the plate itself remains translucent even with micro-prisms located inside said plate. For example when a light flux is directed towards the plate at its bottom; it penetrates inside the plate wherein it is reflected partly onto micro-prisms and by TIR onto bottom and top surfaces of the plate. Said light flux is still transmitted throughout the top surface of the plate and remains conserved on the other side of the plate as well as it would be conserved throughout a transparent plate. On the other hand, intensity distribution of the light flux is perturbed which means that the plate is acting as a translucent material.
Still another advantage is that the illumination device may be operated under white light illumination. No significant wavelength dependence occurs in the near UV, visible and near IR.
Reflectivity of the device according to the invention may be optimised to obtain a desired divergence and intensity distribution of the output light beam. Reflectivity is depending of the number of prisms aligned in the plate. To get a uniform illumination, reflectivity should be distributed between prisms with a 1/N law, where N is the micro-prism number. For example, in a plate wherein 4 micro-prisms are aligned at equal distance; a uniform output light beam will be obtained when 25% reflectivity is obtained at the first micro-prism close to a light source, 33% reflectivity at the second micro-prism, 50% at the third and 100% at the last one at the end of the plate.
The reflectivity of the device may be varied through the plate as a function of the distance between the light source and each micro-prism, by modifying physical characteristics of said micro-prism or by modifying the micro-prism reflective surface. The physical characteristics of the micro-prisms and the thickness of the reflective surface coating may be varied and optimised to obtain the desired output
Cariaso Alan
Jacobson & Holman PLLC
Universite De Liege
LandOfFree
Light guiding plate with internal micro-prisms does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light guiding plate with internal micro-prisms, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light guiding plate with internal micro-prisms will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3128337