ILLUMINATION APPARATUS PROVIDING INCREASED RADIANCE

Field of Invention

The present invention relates to illumination apparatus, and more particularly to illumination apparatus providing enhanced radiance.

Background of the Invention

A characteristic of an illumination device is radiance (L). Radiance of a source is defined by the following equation.

L = P(0)/ (A * cosø * ω) Equation 1

where A is an area of the emitting surface of the source (e.g., measured in square millimeters), P(0) is the radiant power of light emitted by the area A of the source (e.g., in watts) as a function of angle 0,

ω is solid angle (e.g., in steradians) into which the area emits the light, and 0 is the angle relative to the normal of the emitting surface.

Assuming a given power input (e.g., watts of electrical power), radiance is generally thought to be invariant for a given source. However, it would be desirable to increase radiance of a given source.

Summary Aspects of the present invention are directed to apparatus and methods for increasing radiance of a source.

A first aspect of the invention is directed to an illumination apparatus comprising an emitter surface having a reflectivity of at least 30% and a reflector. The reflector being configured and arranged to receive light from the emitter surface and to reflect at least 50% of said light back onto the emitter surface.

In some embodiments, the emitter surface comprises an integral portion of a light source. For example, the emitter surface may comprise a surface of an LED die.

The emitter surface may be planar. The reflector may be a metallic or dielectric mirror. In some embodiments, at least one of the emitter surface and the reflector comprises a concave reflective surface.

The reflector may be disposed on an emitter encasement. The reflector may comprise a planar reflective surface. The reflector may comprise at least two optical components. In some embodiments, the reflector comprises at least one emitter surface.

Another aspect of the invention is directed to an illumination apparatus comprising a first emitter surface, and a reflector comprising a second emitter surface, the reflector configured and arranged to receive light from the first emitter surface and to reflect a portion of said light back onto the first emitter surface.

In some embodiments, the first emitter surface is planar, the second emitter surface is planar and the reflector further comprises a curved reflective surface. In some embodiments, the reflector comprises a third emitter surface, and the second emitter surface and third emitter surface configured and arranged to receive light from the first emitter surface and to reflect a portion of said light back onto the first emitter surface.

Another aspect of the invention is directed to an illumination apparatus comprising a first emitter surface; and a second emitter surface emitting light, adapted to direct a portion of the light onto the first emitter surface, the first emitter surface subtending a solid angle of greater than 5*10 ^"3 srad (e.g., corresponding to a cone having an angle of approximately 5°) for a point on the second emitter surface.

The apparatus may further comprise a third emitter surface emitting second light, adapted to direct a portion of the light onto the second emitter surface, the second emitter surface subtending a solid angle of greater than 5*10 ^"3 srad for a point on the third emitter surface, the first emitter surface, the second emitter surface and third emitter surface arranged such that the second light is reflected by the second emitter surface onto the first emitter surface.

In some embodiments, the first emitter surface emits light having a first spectral content and the second emitter surface emits light having a second spectral content. The first emitter surface may emit light of a first color and the second emitter surface may emit light of a second color.

Yet another aspect of the invention is directed to an slit scan apparatus for use in measuring a subject's eye, comprising a slit projection apparatus an imaging apparatus

for receiving images including a portion of the light after the light is scattered by the eye. The slit projection apparatus comprises I) an illumination apparatus and a slit, the illumination apparatus and slit arranged such that the light in the output is directed onto the eye. The illumination apparatus comprises a first emitter surface, and a reflector comprising a second emitter surface, the reflector configured and arranged to receive light from the first emitter surface and to reflect said light back onto the first emitter surface, the light reflected by the first emitter surface into an output.

In some embodiments, the reflector is configured and arranged to receive the light from the first emitter surface and to reflect at least 50% of said light back onto the first emitter surface. In some embodiments, the second emitter surface emits a second light, the second emitter surface adapted to direct a portion of the second light onto the first emitter surface, the first emitter surface subtending a solid angle of greater than 5*10 ^"3 srad for a point on the second emitter surface.

Still another aspect of the invention is directed to a method of illumination, comprising directing light from an emitter surface having a reflectivity of at least 30% onto a reflector, and reflecting at least 50% of said light back onto the emitter surface.

In some embodiments, the light is reflected from the emitter surface directly into an output of the apparatus, the output being non-coaxial with light directed onto the emitter surface by the reflector. In some embodiments, the light in the output is non- coherent.

Another aspect of the invention is directed to a method of illumination, comprising providing a first emitter surface, providing a reflector comprising a second emitter surface, directing light from the first emitter surface onto the reflector including onto the second emitter surface, and reflecting a portion of said light back onto the first emitter surface.

Another aspect of the invention is directed to a method of illumination comprising directing light from a second emitter surface onto a first emitter surface, the first emitter surface subtending a solid angle of greater than 5* 10 ^"3 srad for a point on the second emitter surface.

Brief Description of the Drawings

Illustrative, non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which the same reference number is used to designate the same or similar components in different figures, and in which:

FIGs. 1-10 are schematic illustrations of examples of illumination apparatus according to aspects of the invention; and

FIG. 11 is a schematic illustration of an example of a slit scan instrument for use in measuring a subject's eye, the instrument including an illumination apparatus according to aspects of the present invention.

Detailed Description

According to aspects of the present invention, light in a first solid angle is projected by a reflective emitting surface onto a reflector and a portion of the light is reflected back onto the emitter surface by the reflector. The emitter surface reflects the light received from the reflector into an output having a second solid angle. It will be appreciated that the light projected into the second solid angle will be substantially equal to a sum of 1) the light projected into the second solid angle by emission of light from the emitting surface directly into the second solid angle, and 2) the light projected into the first solid angle which is reflected by the reflector back onto the emitter surface and then reflected by the emitter surface into the second solid angle. It will be further appreciated that, by so increasing the light in the second solid angle and by maintaining the emitting area constant, the radiance in the second solid angle is increased over what the radiance in the second solid angle would have been in the absence of the reflector. FIG. 1 is a schematic illustration of one example of an illumination apparatus 100 according to aspects of the present invention. Illumination apparatus 100 comprises an emitter 110 having emitter surface 112 and a reflector 120. Reflector 120 is configured and arranged to receive light from the emitter surface and to reflect at least 50% of said light back onto the emitter surface. A representative portion of the emitter surface emits light into first solid angle ωi onto the reflector. The reflector reflects at least 50% of the light in solid angle ωi back onto emitter surface 112 to increase radiance in an output O

having a solid angle ω ₂ . In some embodiments, solid angle ωi is equal to solid angle ω ₂ ; however, said solid angles need not be equal.

The emitter may be any suitable emitter for which light emerges from an emitter surface of the emitter and for which the emitter surface is suitably reflective as discussed in greater detail below. In some embodiments, the emitter may be a light source. For example, the emitter may comprise an LED having a light-emitting semiconductor die a surface of which forms the emitter surface (i.e., the die generates photons due to recombination of electrons and holes). However, in some embodiments the emitter is not a light source. Regardless of whether the emitter is a light source or not, at least a portion of the light emitted by the emitter emerges from the emitter surface (so as to introduce light into a light path) and the emitter surface is suitably reflective. Apparatus arranged according to aspects of the present invention are particularly useful in for improving the output emitters (or emitter surfaces) that output non-coherent light, and where non-coherent light is to be produced in output O. In the illustrated embodiment, emitter surface 112 is planar. However, the emitting surface can have any suitable shape.

In some embodiments, the emitter surface may be an integral part of a light source (e.g., a surface of the LED die). Other embodiments in which the emitter surface forms an integral part of a light source may include, for example, a heated piece of metal having a suitably reflective emitter surface.

Typically the emitter surface will have a reflectivity of at least 30% and in some embodiments, at least 40%. However, by increasing reflectivity, the radiance of an illumination apparatus can be increased. For example, some LEDs have been found to have an emitter surface having a suitable reflectivity. Examples of suitable LEDs include model numbers LXHL_LB3C, LXK2 PR14 R01, both of said LEDs are Luxeon LEDs from Phillips Lumileds Corporation.

In the illustrated embodiment, reflector 120 comprises, for example, a metallic mirror. However, any suitable reflector having a reflectivity greater than about 50% may be used. For example, the reflector can be a dielectric mirror. In some embodiments, a dielectric mirror having a reflectivity greater than 98% may be used. Generally, by increasing reflectivity of the reflector, the radiance of an illumination apparatus can be increased. It will be appreciated that, the lower the reflectivity of the reflector, the

greater the portion of the light reflected by the reflector that must be directed back onto the emitter surface to achieve at least 50% of said light being reflected back onto the emitter surface.

Generally, the larger the solid angle containing light subtended by the reflector, the better the irradiance (radiant power per area). In some embodiments, a condenser lens 130 may be used to control the rays in output of the illumination apparatus.

To achieve a configuration in which light from the emitter surface is received by the reflector and at least 50% of said light is reflected back onto the emitter surface, the mirror is preferably positioned in front of the emitter surface and angled to reflect light back toward the emitter surface. The reflector is selected to have an appropriate shape to reflect the light back onto the emitter. In some embodiments, one or both of the emitter surface and reflector has a concave reflective surface to converge light. In FIG. 1 , where the emitter surface comprises a planar emitter surface, the reflector may have a spherical shape such that light in solid angle ω| is gathered and reflected back onto the emitter surface. Several additional examples of suitable shapes and configurations for emitter surfaces and reflectors are shown below. However, other techniques for collecting light may be used.

It will be noticed that an output of the illumination apparatus is projected into a cone that forms an angle 0 with a normal of the emitting surface. Typically angle 0 is in the range 10-80 degrees. Although, term cone is used, it will be appreciated that the output light can be projected into any suitable shape. In the illustrated embodiment, the light output forms an angle with the normal of the emitter surface of about 50 degrees. It will be appreciated that the output path is non-colinear with the path from the reflector to the emitting surface. FIG. 2 is a schematic illustration of another example of an illumination apparatus

200 according to aspects of the present invention. In FIG. 2, the apparatus comprises an emitter 210 having a curved emitter surface 212, and a reflector 220 having a planar shape. Although the reflector is planar, the curved emitter surface facilitates light being reflected back onto the emitter by reflector 220. As stated above, the reflector should have an appropriate shape to reflect a suitable portion of the light back onto the emitter. It will be appreciated that when the emitter has an emitter surface that produces convergent light, reflector 220 need not be as convergent or need not convergent at all.

FIG. 3 is a schematic illustration of another example of an illumination apparatus 300 according to aspects of the present invention. In FIG. 3, emitter 310 comprises a flat emitter surface 312 and a curved reflector 320 that is disposed on an emitter encasement 314 (e.g., an integrated plastic lens manufactured using conventional techniques). In some embodiments, the encasement is directly connected to the emitting surface (i.e., the encasement is formed with no air gap between the encasement and the emitting surface). Light is gathered and converged back onto the emitter by reflector 320. It will be appreciated that an apparatus as shown in FIG. 3 may be achieved, for example, by depositing a reflector onto a suitably-shaped encasement lens that is directly connected to the emitting surface of the LED die.

FIG. 4 is a schematic illustration of another example of an illumination apparatus 400 according to aspects of the present invention in which the emitter 410 comprises a curved emitter surface 412 (as described above with reference to FIG. 2) and a reflector 420 has a planar shape. Accordingly, the curved emitter surface facilitates light being reflected back onto the emitter by reflector 420. Also, similar to FIG. 3, reflector 420 may be disposed on an emitter encasement 414 that is directly connected to the emitting surface of the source; however, in FIG. 4, the surface on which the reflector is deposited is planar.

FIG. 5 is a schematic illustration of another example of an illumination apparatus 500 according to aspects of the present invention in which an emitter 510 comprises a planar emitter surface 512 and a planar reflector 520; however, apparatus 500 comprises an optical element 530 having positive power (e.g., a biconvex lens, a diffractive element) such that light is gathered and converged prior to, and after, being reflected from the reflector. In such embodiments, performance may be enhanced by coating the optical element with an antireflection coating tuned to the wavelength at which the LEDs emit light.

FIG. 6 is a schematic illustration of another example of an illumination apparatus 600 comprising a planar emitter surface 512 and a planer reflector 520; however, apparatus 500 comprises a convergent optical element (e.g., a biconvex lens) that is integrally formed with an encasement 614 which is directly connected to the emitting surface of the emitter. Similar to FIG. 5, light is gathered and converged prior to, and after being, reflected from the reflector.

It will be appreciated that in the apparatus as illustrated in FIGs. 1-6, the components are configured such that a portion of light is projected directly from an reflective surface into output O and other light in the output reflects off the emitter surface at most one time before entering an output O. Light in the output is formed by reflection from an emitter surface. It will also be appreciated that output pathway is not coaxial with the pathway from the reflector to the emitter surface.

Although the above embodiments illustrate illumination apparatus having an emitter surface in combination with a reflector comprising only one reflector element to suitably reflect light back onto the emitter surface, in other embodiments, a reflector may comprise two or more optical elements (including one or more mirrors, one or more lenses or other optical element) to direct light back onto the emitter surface. Generally, adding additional optical elements will add complexity and reduce the efficiency with which light is transmitted back onto emitter surface; however, in some embodiments, multiple elements may be advantageous. Another aspect of the invention is directed to cascading two or more emitter surfaces to further increase the radiance of a source in a given output. In embodiments according to this aspect, an emitter surface forms a reflector (or the emitting surface forms an element of a multi-element reflector) that operates to direct light along a path such that the light is suitably reflected onto another emitter surface. The radiance is increased beyond that of a single emitter surface in the manner described above. It will be appreciated that the emitter surface along the path operates as an active reflector (i.e., a reflector capable of adding light to the light directed along the path).

In embodiments having more than one emitter surface, the emitter surfaces may be configured the same as one another or different than one another. For example, in embodiments where the emitter surfaces are portions of LEDs, the LEDs may be LEDs of a same model number or may have different model numbers or LEDs manufactured by different manufactures. The emitter surfaces may be portions of different types of devices (e.g., one of the emitter surfaces is a portion of an LED and another emitter surface is a portion of another type of device). Some embodiments having more than one emitter surface comprise a first emitter surfaces, and a reflector comprising a second emitter surface, the reflector configured and arranged to receive light from the emitter surface and to reflect a portion of said light

back onto the emitter surface. In some embodiments, the reflector is configured and arranged to receive light from the emitter surface and at least 50% of said light is back onto the emitter surface; however, due to the active nature of the reflector, less than 50% may be needed to achieve a useable output radiance. For example, the amount may be greater than 20% of said light.

FIG. 7 is a schematic illustration of another example of an illumination apparatus 700 comprising a first planar emitter surface 712, a lens 740 to direct light onto a second planar emitter surface 732, and a curved reflector 720 (i.e., a curved reflective surface). It will be appreciated that light in output O is formed in part by each of the following: light emitted directly from emitter surface 712 into output O; light emitted from emitter surface 732 onto emitter surface 712 and into output O; light emitted from emitter surface 732 onto reflector 720, back onto emitting surface 732 onto emitter surface 712 and then into output O; and light emitted from emitter surface 712 onto emitter surface 732, then onto reflector 720 back onto emitter surface 732, back onto emitter surface 712 and into output O.

It will be appreciated that, in apparatus 700, a reflector 725 (comprising reflector 720, emitter surface 732 and lens 740) is configured and arranged to receive light from emitter surface 712 and to reflect a portion of said light back onto emitter surface 712. FIG. 8 is a schematic illustration of another example of an illumination apparatus 800 comprising a first planar emitter surface 812, a first lens 840 connected to the emitter surface 812 (e.g., as described above with reference to FIG. 3), a second emitter surface 832, a second lens 850 connected to the emitter surface 832, and a planar reflector 820 to direct light back onto emitter surface 832.

It will be appreciated that, in apparatus 800, a reflector (comprising reflector 820, emitter surface 832 and lenses 840 and 850) is configured and arranged to receive light from the emitter surface 812 and to reflect a portion of said light back onto emitter surface 812. Similar to apparatus 700 (shown in FIG. 7), second emitter surface 832 operates as an active reflector. The light paths into output path O of the illumination apparatus are similar to those in FIG. 7. It will be appreciated that in the apparatus as illustrated in FIGs. 7-8, the components are configured such that light reflects off an emitter surface at most two times before entering an output O. Light in the output is formed by reflection from an

emitter surface. It will also be appreciated that output pathway is not coaxial with the pathway from the reflector to the emitter surface.

FIG. 9 is a schematic illustration of another example of an illumination apparatus 900 comprising ten planar emitter surfaces 912 _M o each of 912], 912 ₃ , 912s, 912 ₇ , 912 ₉ are formed on a common substrate, and each of 912 ₂ , 912 ₄ , 912 ₆ , 912s, 912JO are formed on a common substrate. Each emitter surfaces 912i,j ₀ has a corresponding lens 94OM ₀ connected thereto. A planar reflector 920 is arranged to direct light from emitter surface 912 ₁₀ back onto emitter surface 912 ₁₀ such that a portion of the light from each of the emitter surfaces propagates in the direction of reflector 920 and is redirected back into the output of the illumination apparatus. Additionally, a portion of the light from each emitter surface propagates in the direction of output O (i.e., away from reflector 920). It will be appreciated that 10 emitter surface 912 _t - 912io is shown by way of example. Any suitable number may be used. For example, apparatus may include at least three emitter surfaces. Additionally, emitters, lenses and/or mirrors may be directly connected together to form common packages with one another. Alternatively, said emitters, lenses and/or mirrors may be formed as discrete components.

It will be appreciated that, in apparatus 900, a reflector (comprising reflector 920, emitter surfaces 912M _O ) is configured and arranged to receive light from the emitter surface 912i and to reflect a suitable portion of said light back onto emitter surface 912[. It will also be appreciated that, for a selected one of the other emitter surfaces 912 ₂ -io in apparatus 900, a reflector reflecting a suitable amount of light back onto the selected emitter surface can be identified.

FIG. 10 is a schematic illustration of another example of the illumination apparatus 1000 comprising ten planar emitter surfaces 912]. io each having a lens 94OM ₀ as shown in FIG. 9. However, in apparatus 1000 planar reflector 920 (shown in FIG. 9) is omitted such that illumination apparatus has a first output Oi and a second output O ₂ . Each output has an enhanced radiance. Of course, the radiance of each output is less than the radiance in the single output of apparatus 900 (shown in FIG. 9).

It will be appreciated that unlike other embodiments described herein, apparatus 1000 does not include any reflective surface (e.g., a reflector element or a reflective emitter surface) configured and arranged to receive light from an emitter surface and to reflect at least a portion of said light back onto the emitter surface. Instead, radiance in

an output O ₁ or O ₂ is increased by appropriately directing a portion of light from a second emitter surface onto a first emitter surface (e.g., 912 ₂ being an example of such a second emitter surface and 912i being an example of such a first emitter surface in FIG. 10). Typically, an apparatus is configured such that a first emitter surface receives light in a solid angle (θ) of greater than 0.005 *10 ^"3 steradians (srad) (which corresponds to a cone of approximately 5°) for a point on a second emitter surface (e.g., 9H ₁ being an example of first emitter surface and 912 ₂ being an example of a second emitter surface in FIG. 10). It will be appreciated that one or more optical elements may gather light within the solid angle and direct the light to first emitter surface to achieve such an arrangement (e.g. 94O ₁ and 94O ₂ collect light emitted by the second emitter surface and direct the light onto the first emitter surface). In some embodiments, the solid angle is greater than 0.02 srad (which corresponds to a cone of approximately 10°), and some embodiments the solid angle is greater than 0.2 srad (which corresponds to a cone of approximately 30°). It will be appreciated that the relevant solid angle subtended by a first emitting surface is a solid angle into which second emitting surface is adapted to project light.

In some embodiments, the apparatus comprises a third emitter surface (912 ₃ ) emitting second light. The third emitter surface is adapted to direct a portion of the second light onto the second emitter surface. Similar to the arrangement having the first emitter surface and the second emitter surface, such apparatus (i.e., including a third emitter surfaces) are configured such that a second emitter surface receives light in a solid angle of greater than 5*10 ^"3 srad for a point on the third emitter surface. It will be appreciated that the first emitter surface, the second emitter surface and third emitter are arranged such that the second light is reflected by the second emitter surface onto the first emitter surface.

Generally, increasing the number of LEDs cascaded in such a manner as described above increases radiance in an output. Also, it will be appreciated that the larger the solid angle subtended by the reflector, the better irradiance (power per area) of the illumination apparatus; however, a larger solid angle does not significantly change radiance.

Although the illustrated embodiment in FIG. 10 includes ten LEDs in a cascade, embodiments of illumination apparatus according to this aspect of the invention can include two or more LEDs. hi some embodiments having multiple emitters (as shown in FIGs. 7-10), at least two emitter surfaces emit light having different spectral content than one another (e.g., the emitter surfaces emit light of different colors), hi one example, one emitter surface emits blue light and another emitter surface emits yellow light. It will be appreciated that such arrangements permit a light output to be of a different color than either of the sources. In some such embodiments, the light output from the emitter surfaces is variable, so that the color of the light output of the apparatus can be varied. For example, the output may be white light.

FIG. 11 illustrates a slit scan apparatus 1100 for use in measuring a subject's eye. The slit scan apparatus includes a slit projection apparatus 1110, an imaging apparatus 1130 for receiving images of slit light after slits of light are scattered by eye E, and a processor 1140 for controlling the apparatus (e.g., slit projection apparatus 1110 and imaging apparatus 1130) and achieving a representation of the eye from the images. The apparatus may be configured as a conventional slit scan apparatus other than that the slit projection apparatus includes an illumination apparatus 1115 as described above. Illumination apparatus 1115 may be any suitable illumination apparatus as described above. In some embodiments of slit scan apparatus, the light emitted by the illumination apparatus will be infrared.

Light from illumination apparatus 1115 is projected through a slit 1120 (e.g., an opaque medium having a long, thin aperture formed therein) onto the subject's eye E to obtain multiple images of the eye, each image being obtained with the light projected onto a different portion of the eye. Such slit scan apparatus are described for example in U.S. Patents 5,512,965, 5,512,966 both to Snook, the substance of said patents is hereby incorporated by reference. To project light onto different portions of an eye, one or more components of the projection apparatus may be moved. It will be appreciated that illumination apparatus as described herein can be used in place of lamp 20 in FIG. 2 of said patent. Advantageously, as described above, the illumination apparatus provides radiance that is greater than could be obtained with a convention illumination source thereby improving the quality of the images and measurements of the subject's eye.

Typically the emitting surfaces in the illumination apparatus will be LEDs due to their long life and relatively low cost; however, any suitable emitting surface as described above may be used.

Having thus described the inventive concepts and a number of exemplary embodiments, it will be apparent to those skilled in the art that the invention may be implemented in various ways, and that modifications and improvements will readily occur to such persons. Thus, the embodiments are not intended to be limiting and presented by way of example only. The invention is limited only as required by the following claims and equivalents thereto.