Elongated LED lighting arrangement

An elongated LED lighting arrangement comprises an elongated light pipe with homogeneous optical material between first and second ends. In an exemplary embodiment, an LED provides blue light to the light pipe via a first dichroic mirror tuned to pass blue light. Down-converting means on sidewall of the light pipe, tuned to receive blue light, absorbs blue light from the LED and to emit lower-energy light outside of the light pipe at respectively higher wavelengths. Light-extracting means on the sidewall extract from the light pipe some blue light without changing the wavelengths of the foregoing light. Light from the down-converting means and the light-extracting means are combined to provide a composite color. The first dichroic mirror receives some light emitted by the down-converting means and reflects back into the light pipe more than 80 percent of the light received by the mirror.

FIELD OF THE INVENTION

The present invention relates to an elongated LED lighting arrangement comprising various light wavelength-tuned components for increasing efficiency.

BACKGROUND OF THE INVENTION

Various elongated LED lighting arrangements for general illumination have been proposed in the prior art. Many of such arrangements suffer from low efficiency in conversion of electricity to light, and also suffer from producing light with a color temperature that may be less than pleasing to many viewers.

It would be desirable to provide elongated LED lighting arrangements whose efficiency in converting electricity to useful light is enhanced, and having a light output whose color temperature can be more aesthetically pleasing, such as by exhibiting a warmer color temperature light.

BRIEF SUMMARY OF THE INVENTION

In a preferred form, an elongated LED lighting arrangement comprises an elongated light pipe extending between first and second ends. The light pipe has a sidewall between the ends facing outwardly of the light pipe. The light pipe comprises homogeneous optical material between the ends. A first LED light source comprises at least one LED tuned to efficiently provide to the light pipe, via the first end, light within a first wavelength band. A first dichroic mirror is interposed between the first LED light source and the first end. The mirror is tuned to pass more than 90 percent of light within the first wavelength band from the first LED light source into the light pipe via the first end. Down-converting means on the sidewall is tuned to efficiently absorb light rays from the first LED light source within a wavelength range that includes at least 80 percent of the first wavelength range and to emit lower-energy light rays outside of the light pipe at respectively higher wavelengths. Light-extracting means on the sidewall extract from the light pipe some light rays within the first wavelength band without changing the wavelengths of the foregoing light. The down-converting means and the light-extracting means are arranged so that the light emitted by the down-converting means and the light extracted from the light pipe by the light-extracting means intermix to produce light, the majority of which has a composite color determined by the foregoing light emitted and the foregoing light extracted. The first dichroic mirror receives some light emitted by the down-converting means and reflects back into the light pipe more than 80 percent of the light received by the mirror, so that the reflected light can be extracted from the side of the light pipe by the light-extracting means.

The foregoing elongated LED lighting arrangement beneficially has enhanced efficiency in converting electricity to useful light in comparison with many prior art arrangements, and also has a light output whose color temperature can be more aesthetically pleasing, such as by exhibiting a warmer color temperature light.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This description describes three preferred embodiments of elongated lighting arrangements, one having symmetrical ends and the other two having non-symmetrical ends.

Symmetrical Embodiment

FIG. 1shows an elongated lighting arrangement100comprising a light pipe112, which may comprise a cylindrical acrylic polymer rod, by way of example. Other details of suitable light pipes are described below. Light within a first wavelength range, preferably blue light, is provided to associated ends of light pipe112by light sources114and120, each of which comprises one or more LEDs preferably tuned to blue light. Blue light LEDs are presently preferred, because such LEDs are highly efficient in converting electricity to light. By “tuned” is meant herein that the component in question is designed in a way so as to enhance or even optimize some aspect of the “object” which is tuned, whereby, for instance, tuning of LEDs to blue light means that the LEDs are designed so as to enhance or even optimize blue light emission.

LED light sources114and120each comprise one or more LEDs for producing blue light, typically with a common lens115and121, respectively.

A notch dichroic mirror117is interposed between light source114and the left-shown end of light pipe112, and a further notch dichroic mirror123is interposed between light source120and the right-shown end of light pipe112. Each of notch dichroic mirrors117and123is tuned to pass more than 90 percent of light within the mentioned first wavelength range, and which preferably is for blue light. The mirrors117and123may be angled as shown to increase overall efficiency, but many other orientations and shapes, including multi-faceted shapes, will be routine to persons of ordinary skill in the art from the present specification.

Preferably interposed between LED light source114and notch dichroic mirror117is a light coupler118. Light coupler118is configured to condition the angular distribution of light to promote total internal reflection of such light within the light pipe. A similar light coupler124is preferably interposed between LED light source120and notch dichroic mirror123, and is also configured to condition the angular distribution of light to promote total internal reflection of such light within the light pipe

Shown atop light pipe112is a down-converting and light-scattering means130, whose cross section is shown in any of alternativeFIG. 2,3or4.

FIG. 2shows down-converting and light-scattering means130ofFIG. 1as a phosphor layer132, usually within a suitable binder, atop light pipe112. Some material in the phosphor layer can absorb light at one wavelength and emit higher-wavelength light at a lower energy; hence, the term “down-converting” means as used herein. Some material in a phosphor layer that is applied to a light pipe can act as a light scatterer so as to extract light from the light pipe and emit it from a sidewall of the light pipe at the same wavelength. The term “light-scattering means” or variants are used herein to indicate the foregoing type of light extraction without changing the wavelength of light. Thus, the phosphor layer132acts as both a down-converting means and a light-scattering means.

Where a greater extent of extraction of light from the sidewall of light pipe112by a light-scattering means at the same wavelength is desired, the down-converting and light-scattering means130ofFIG. 1can also incorporate a more traditional light-scattering material. Thus,FIGS. 3 and 4show the incorporation of titania, as indicated by the small x-shaped particles to contrast with dots used to portray phosphor.FIG. 3shows titania and phosphor intermixed in down-converting and light-scattering means134, whereasFIG. 4shows one example of stripes136of phosphor and interspersed stripes138of titania, which would each have a suitable binder, and could be oriented in other directions than along the main path of light propagation from end to end of light pipe112.

Other forms of down-converting means, such as quantum dots or dyes can be used instead of phosphor, and other forms of light-scattering means can be used instead of titania as will be further described below.

FIG. 1shows two exemplary blue light rays150and160, which are shown with short wavelength sinusoidal waveforms, for explaining the operation of elongated lighting arrangement100.

Exemplary upper blue light ray150emitted by light source114strikes down-converting and light-scattering means130at the top of light pipe112, and causes one of several alternative light rays152,154and156to emerge. These light rays152,154and156are alternative light rays resulting from absorption of blue light ray150by the down-converting aspect of down-converting and light-scattering means130, which is tuned to receive blue “excitation” light and emit light at higher wavelengths. Since the wavelengths of emission from the foregoing down-converting means will vary, the result to the viewer is preferably white light or another broad wavelength spectrum light. Accordingly, exemplary white light rays152,154and156are shown as a composite of two different frequencies as an indication of a broad wavelength spectrum of light rays, although white light actually comprises many more than two wavelengths of light. The white light rays152,154and156, emitted from the foregoing down-converting means typically radiate in all directions, but only a few exemplary directions are shown.

Since exemplary white light rays152and154are directed upwardly, in similar manner as white light is radiated from a conventional fluorescent lamp tube, it is desirable to capture the upwardly directed light. Accordingly, as shown inFIGS. 2-4, a typically non-specular reflector170can capture and redirect light back downwardly.

InFIG. 1, white light ray156is randomly directed downwardly from the mentioned down-converting means and strikes the notch dichroic mirror117, tuned to pass light in the blue wavelength range. Accordingly, a component of white light ray156in the blue light wavelength range passes through dichroic mirror117as blue light ray157, and typically is lost because it does not contribute to side-light extraction from elongated lighting arrangement100. However, higher wavelength light158, referred to herein as “quasi-white light,” is saved and converted to useful light by being reflected from notch dichroic mirror117. Quasi-white light ray158is then totally internally reflected from the bottom sidewall of the light pipe112in a direction from left to right. The totally internally reflected quasi-white light ray158then reaches the down-converting and light-scattering means130. The down-converting aspect of such means130is not tuned to quasi-white light ray158, which is at higher wavelength than blue light, but rather is tuned to blue light as mentioned above, and so the light-scattering aspect of means130scatters light ray158in a downward direction.

A light mixing region174, shown beneath light pipe112signifies that light of various colors is mixed together, such as quasi-white light ray158, blue light ray162and white light ray167. Light rays158,162and167do not totally internally reflect within light pipe112, due to their high angle with respect to a main path of light propagation through the light pipe between the left- and right-shown ends of such light pipe. However, mixing of light of various colors occurs in other places as well, including within light pipe112and also as a result of typically white light being reflected downwardly from the reflector170shown inFIGS. 2-4. Preferably, the composite color of resulting light is white with a color temperature between 2700 K and 4500 K, and more preferably, with a color temperature between 2700 K and 3500 K.

InFIG. 1, the second blue light ray160strikes the down-converting and light-scattering means130at the top of light pipe112, whereupon the light-scattering aspect of such means130scatters light ray160downwardly.

FIG. 1further shows LED light source114emitting a blue light ray165that reaches and is absorbed by the down-converting aspect of the down-converting and light-scattering means130at the top of light pipe112. As a consequence, the down-converting and light-scattering means130emits white light ray167, which is randomly directed downwardly to enter light mixing region174.

Typically, the right- and left-shown halves of elongated lighting arrangement110ofFIG. 1are symmetrical to each other, Therefore, the interaction of blue light from LED light source120with down-converting and light-scattering means130is the same as the interaction of blue light from LED light source114with such means130.

Tuning of LEDs, Notch Dichroic Mirror and Down-Converting Means

In conformity with the above definition of “tuned,” the word “tuning” means herein that a component in question is designed in a way so as to enhance or even optimize some aspect of the “object” which is tuned, whereby, for instance, tuning of LEDs to blue light means that the LEDs are designed so as to enhance or even optimize blue light emission. Such designing (or tuning) is done before manufacturing a component. More description is now provided for of tuning components such as the LEDs used in light sources114and120, the notch dichroic mirrors,117and123and the down-converting aspect of the down-converting and light-scattering means130.

As mentioned above, the LEDs of light sources114and120are preferably tuned to efficiently convert electricity to light. With presently available LEDs, maximum efficiency has been attained converting electricity to blue light.FIG. 5helps explain “tuning” characteristics for the mentioned blue LEDs, notch dichroic mirrors17and23and down-converting and light-scattering means130. In particular, FIG. shows preferred wavelength characteristics for the foregoing components.

InFIG. 5, exemplary LED Spectral Power Distribution extends from about 400 nm to about 520 nm, but more than 95 percent of its spectral range preferably falls within a range180extending from about 430 nm to about 485 nm. A preferred LED may be those sold by Cree, Inc. of Durham, N.C. USA, under Product Code XLamp XT-E Royal Blue LEDs. Beneficially, the illustrated, preferred Excitation Wavelength Range of Down-Converting Means includes the foregoing wavelength range180. An exemplary Down-Converting Means comprises a phosphor sold by Intematix of Fremont, Calif., USA, under Product Code NYAG4653, by way of example. Accordingly, the blue light from the LEDs can be efficiently converted to another color spectrum, such as white, by the down-converting means.

Tuning of the notch dichroic mirrors117and123to efficiently pass blue light from the LEDs to the light pipe112is achieved where the illustrated Notch Mirror Transmission Profile is broad enough to efficiently pass more than 80 percent or more preferably 95 percent of blue light from the LEDs the light pipe112.

For certain wavelengths of light, an alternative to a notch dichroic mirror is a dichroic mirror incorporating a cut-off filter. Thus, to illustrate the replacement of a notch dichroic mirror tuned to blue light with a dichroic mirror incorporating a cut-off filter,FIG. 5shows alternative portion of the notch Dichroic Mirror Transmission Profile labeled500that would replace left-shown portion502.

First Non-Symmetrical Embodiment

FIG. 6shows an elongated lighting arrangement600whose ends are not symmetrical to each other. The left-shown end of arrangement600includes a LED light source614, a notch dichroic mirror617and a light coupler618that correspond to the LED light source114, notch dichroic mirror117and light coupler118ofFIG. 1. However, the right-shown LED light source620, preferably providing white light, differs from LED light source120ofFIG. 1that preferably provides blue light. Additionally, there is no notch dichroic mirror on the right-hand side of elongated lighting arrangement600to correspond with the notch dichroic mirror123ofFIG. 1, and right-shown light coupler624inFIG. 6consequently differs in shape from right-shown light coupler624inFIG. 1. Such light coupler624may be formed integrally or separately from the light pipe112. Finally, the down-converting and light-scattering means630corresponds with the down-converting and light-scattering means130ofFIG. 1.

In operation, the left-hand components of elongated lighting arrangement600ofFIG. 6operate in a similar manner to the left-hand components of elongated lighting arrangement100ofFIG. 1. Therefore, only the parts of light rays158and160that extending into light mixing region174are shown inFIG. 6, and the reader is referred to the above description concerning the foregoing light rays.

FIG. 6shows two exemplary white light rays640and642from LED light source620. White light ray640is directed to the left and upwardly where it strikes down-converting and light-scattering means630at the top of light pipe112and is scattered downwardly into light mixing region174. Segments of light rays158,160and167, which are fully shown inFIG. 1and described in connection withFIG. 1, also enter light mixing region174so as to intermix with light ray640. White light ray642travels straight through light pipe112, and reaches notch dichroic mirror617. The blue part644of white light ray642passes through notch dichroic mirror617, tuned to blue light as is notch dichroic mirror117ofFIG. 1, and typically is lost because it does not contribute to side-light extraction from elongated lighting arrangement600. However, higher wavelength light646, referred to as a “quasi-white” light ray646, is saved and converted to useful light by being reflected from notch dichroic mirror617, striking down-converting and light-scattering means630, and being scattered downwardly into light mixing region174.

Second Non-Symmetrical Embodiment

FIG. 7shows an elongated lighting arrangement700whose ends are not symmetrical with each other. The left-shown end of arrangement700includes an LED light source714, a notch dichroic mirror717and a light coupler718that correspond to the LED light source114, notch dichroic mirror117and light coupler118ofFIG. 1. Light coupler724, associated with LED light source720, corresponds to light coupler124ofFIG. 1. However, the right-shown LED light source720, which may provide yellow light, differs from LED light source120ofFIG. 1that preferably provides blue light. Additionally, notch dichroic mirror723is tuned to pass yellow light, rather than blue light as is the case for notch dichroic mirror117ofFIG. 1. Finally, elongated lighting arrangement700includes a light-extracting means730, which may differ from the down-converting and light-scattering means130ofFIG. 1, as follows.

“Light-extracting means,” as applies to light-extracting means730ofFIG. 7, connotes herein a means that can extract light by light scattering as described above, that is, without changing wavelength of scattered light, and optionally that can also extract light through a down-converting means as described above, wherein emitted light has a higher wavelength than absorbed light. Accordingly, there are two distinct modes of operation for elongated lighting arrangement700ofFIG. 7.

In the first mode of operation for elongated lighting arrangement700, light-extracting means730comprises light-scattering means as well as down-converting means, as these terms have been defined above. In this case, the light-extracting means730may be embodied, as shown inFIGS. 2 and 3, as down-converting and light-scattering means132or134, or as shown inFIG. 4, as interspersed stripes of phosphor136and titania138.

In the first mode of operation of lighting arrangement700, LED light source714emits a blue light ray745, which passes through notch dichroic mirror717, tuned to pass blue light. Blue light ray745reaches notch dichroic mirror723, and because such mirror723is tuned to yellow light, blue light ray745is beneficially reflected by the mirror upwardly, where it strikes light-extracting means730, resulting in exemplary, alternative light rays747,748and749. Light rays747,748and749are white light rays, due to absorption and reemission by down-converting means in light-extracting means730. White light ray749is directed downwardly and enters light mixing region174. Segments of light rays158,160and167, which are fully shown inFIG. 1and described in connection withFIG. 1, also enter light mixing region174so as to intermix with white light ray749.

As also shown inFIG. 7, in the first mode of operation for lighting arrangement700, wherein light-extracting means730also includes a down-converting means, LED light source720produces an two exemplary yellow light rays750and755. Yellow light ray750is directed so as to strike light-extracting means730, whose down-converting means is tuned to blue light. Therefore, the light-extracting means730does not absorb the yellow light, but only scatters the yellow light ray750downwardly without changing its wavelength. Light ray750reaches light mixing region174, so as to mix with other light rays in such region.

The other yellow light ray755emitted by LED light source720travels all the way across light pipe112and reaches notch dichroic mirror717. Since mirror717is tuned to pass only blue light, yellow light ray755is beneficially reflected from the mirror, strikes light-extracting means730, and is scattered downwardly to reach light mixing region174.

In the second mode of operation of elongated lighting arrangement700, light-extracting means730does not include a down-converting means, as defined above. Therefore, as shown inFIG. 8, the light-extracting means730may be comprised of titania760with a suitable binder, and not phosphor or other down-converting means, as illustrated inFIG. 8. In this second mode of operation, the quasi-white light ray158and white light ray167ofFIG. 1entering the light mixing region174would not be present and would not enter light mixing region174. This is due to the lack of a down-converting means to absorb blue light and remit light at longer wavelengths that characterize light rays158and167.

In the mentioned second mode of operation of lighting arrangement700, the yellow light rays750and755from LED light source720behave the same as in the first mode of operation as described above. This is because the yellow light rays750and755do not interact with any down-converting means in the light-extracting means730of the first mode, which is tuned to blue light, and there are no down-converting means in the second mode.

In the mentioned second mode of operation, the behavior of blue light ray745from LED light source714will differ from behavior in the first mode of operation as follows. Blue light ray745from LED light source714passes through notch dichroic mirror717, tuned to pass blue light, and is reflected from notch dichroic mirror723, tuned to yellow light, in the same manner as described for the first mode of operation. However, since the light-extracting means730lacks down-converting means, when blue light ray745strikes light-extracting means730, there are no absorptions and reemissions as white light rays747and748. But, there is light-scattering of blue light ray745without change of wavelength, from light-extracting means730and into light mixing region174.

The following discussion elaborates on two of the above-described components of the invention elongated LED lighting arrangement; that is, a light pipe and a light-scattering means.

Light Pipe

The light pipe preferably comprises an elongated member, which may be in the form of a solid or hollow rod. By “elongated” is meant being long in relation to width or diameter, for instance, where the “long” dimension can be both along a straight path or a curved path. At least one end of the light pipe receives light from an associated light coupler. The elongated member has an elongated sidewall and light-extracting means along at least part of the elongated sidewall for extracting light through the sidewall and distributing said light to a target area. At least that portion of the light pipe having light-extracting means is preferably solid, although there may exist in the pipe small voids caused by manufacturing processes, for instance, that have insubstantial impact on the side-light light extraction and distribution properties of the pipe.

A light pipe may comprise an acrylic polymer rod, or high-temperature glass or quartz for operation in a heated environment, or other optically clear material such as the core of a large core, flexible, plastic, fiberoptic light pipe.

A light pipe in the form of a rod typically has a cross section along a central path of light propagation through the light pipe that is more round than flat. In such case, or instance, the minimum cross-sectional dimension of the rod s preferably more than 50 percent of the maximum cross-sectional dimension of the rod. In a preferred embodiment, the cross-section of the rod is substantially circular. However, the light pipe is not limited to the form of a rod, and may, for instance, be in the form of a rectangular cross-sectioned slab, with exemplary cross-sectional dimensions of less than about 5 mm in thickness and more than about 25 mm in width. A further, exemplary configuration for a slab is to have a rectangular light-receiving surface of a first width and a rectangular light-transmitting output surface of a substantially larger width, where the height of the slab from light-receiving surface to light-transmitting surface is varied to capture light from an LED, for instance, and spread in out for transmission through the light-transmitting surface.

Preferably, a light pipe is rigid, by which is meant that at 20 degrees Celsius the pipe has a self-supporting shape such that the pipe returns to its original or approximately original (e.g., linear or curved) shape after being bent along a central path of light propagation through the pipe.

Light-scattering means, as that term is defined above to avoid changing wavelengths of light, may be of various types whose selection will be routine to those of ordinary skill in the art. For instance, three types of light-scattering means are disclosed in U.S. Pat. No. 7,163,326, entitled “Efficient Luminaire with Directional Side-Light Extraction,” assigned to Energy Focus, Inc. of Solon, Ohio. In brief, these three types are (1) discontinuities on the surface of a light pipe, (2) a layer of paint on the surface of a light pipe, and (3) a vinyl sticker applied to the surface of a light pipe.

In more detail, (1) discontinuities on the surface of a light pipe may be formed, for instance, by creating a textured pattern on the light pipe surface by molding, by roughening the light pipe surface with chemical etchant, or by making one or more indentations in the side of the light pipe. Secondly, (2) the light-scattering means could comprise a layer of paint exhibiting Lambertian-scattering and having a binder with a refractive index about the same as, or greater than that of, the core. Suitable light-scattering particles are added to the paint, such as titanium dioxide or many other materials as will be apparent to those of ordinary skill in the art. Preferably, the paint is an organic solvent-based paint. Thirdly, (3) the light-scattering means could comprise vinyl sticker material in a desired shape applied to the surface of the light pipe. Appropriate vinyl stickers have been supplied by Avery Graphics, a division of Avery Dennison of Pasadena, Calif. The film is an adhesive white vinyl film of 0.146 mm thickness, typically used for backlit signs.

Generally, the light-scattering means may be continuous or intermittent or partially continuous and partially intermittent along the length of a light pipe, for instance. An intermittent pattern is shown in the above-mentioned U.S. Pat. No. 7,163,326 inFIG. 15A, for instance.

The following is a list of reference numerals and associated parts as used in this specification and drawings:

While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention.