Patent Application
20120155116
Light fixtures provide a source of light to illuminate dark environments. A light fixture can be constructed from a light source placed in contact with a light guide for directing light from the light source into an environment. To improve the efficiency of the light fixture, and to reduce costs associated with illumination, a light emitting diode (LED) module can be used as a light source. A LED-based light fixture, however, may be subject to several mechanisms that reduce the efficiency of the fixture. In some cases, light provided by a LED module may propagate through a light guide and out of a far end (e.g., a trailing edge) of the light guide. This lost light may substantially decrease the efficiency of the light fixture.
LED-based light fixtures having a light guide with a retroreflective element and methods for creating the same are provided. In particular, light fixtures having a LED light source connected to one end of a rectangular prism-shaped light guide array. The end of the light guide array that is opposite the LED light source can be cut or shaped to create a retroreflective element such that light reaching the end of the light guide array may be reflected back into the light guide array.
A LED light fixture can include a LED module serving as a light source. The LED module may provide a light output that is substantially in a Lambertian distribution. To guide the light towards an environment, a light guide array (LGA) can be coupled to the light source such that light from the light source can be redirected towards the environment. In some cases, the LGA can be constructed such that substantially all of the light emitted by the light source may be frustrated by the LGA as it propagates through the LGA. In this manner, light emitted by the LED module can be redirected by the LGA to the environment of the light fixture.
Some of the light emitted by the LED module, however, may propagate through the entire LGA without being frustrated, and may pass through a trailing edge of the LGA. To improve the efficiency of the LGA, the LGA can include a retroreflective element at the trailing edge to redirect light back from the trailing edge towards the LGA. In some cases, the trailing edge can be shaped to include two angled facets forming a point at the trailing edge. The angles of the facets can be selected based on the index of refraction between the material of the LGA and air such that light reaching the facets is reflected internally within the LGA. In particular, if the index of refraction between the LGA and the environment is 1.5, the facets can be angled at more than a critical angle of 42 degrees. To ensure that light reflected by the facets is turned around, the facets can be angled at substantially 90 degrees relative to each other.
The above and other features of the present invention, its nature and various advantages will be more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings in which:
This is directed to an edge-lit LED light fixture having an elongated light guide array (LGA) to which a LED light source is coupled at a first end. A second end of the LGA, opposite the first end, can include at least two angled facets forming a retroreflective element for reflecting light emitted by the LED that reaches the second end back into the LGA.
A light fixture that uses a LED module as a light source can be mounted in several different manners. In some cases, a light fixture can be mounted to a ceiling, mounted under a counter, as part of a desk light, as a wall sconce, as a wall wash, as a surface mounted light fixture, or combinations of these. Light emitted by the LED module can be directed into the environment from the fixture by a light guide array (LGA).
LED module 102 can provide light to LGA 110 using different approaches. In particular, LED module 102 may be placed in contact with or adjacent to first end 112 of LGA 110 such that light enters LGA 110 from first end 112 and is propagated towards second end 114. Light 105 entering LGA 110 can be reflected in part by upper boundary 116 and lower boundary 118. In some cases, reflective component 120 (e.g., a separate reflective element offset from lower boundary 118) can be applied to or near lower boundary 118 to improve the reflectivity of lower boundary 118 and reduce losses of light leaving LGA 110 through lower boundary 118. Some portions 106 of light 105, however, may be frustrated by ribs or other features incorporated in LGA 110, such that portions 106 of light 105 leave LGA 110 through upper boundary 116. These portions 106 may serve to illuminate the environment in which fixture 100 is placed.
LGA 110 can include any suitable waveguide for guiding light waves from a source into an environment. In some cases, LGA 110 can include a slab or planar waveguide, a rib waveguide, or any other type of waveguide. In some cases, LGA 110 can include several guides combining to redirect light from a LED module. Although, in the following discussion, LGA 110 is described as a rectangular prism light guide array, it will be understood that any waveguide can be used with a LED module as part of a light fixture.
LGA 110 can have any suitable size or shape. In some cases, the size and shape used for a particular LGA can vary based on the desired use of a light fixture. For example, LGA 110 can substantially define a rectangular prism having sides that are constrained within planes. Adjacent sides of the LGA can be provided at substantially right angles. The rectangular prism can have any suitable dimensions including, for example, a height of 150 mm (e.g., 6″), a width of 5 mm (e.g., 0.2″) and a length in the range of 300 mm to 2500 mm (e.g., 1′ to 8′).
In some cases, LGA 110 can include a non-rectangular three-dimensional shape. For example, LGA 110 can include a triangular prism, or any other non-rectangular polygonal prism. As another example, LGA 110 can include one or more sides that are not planar (e.g., curved surfaces). LGA 110, however, may include at least one elongated side such that a LED module is only provided on one end of the elongated LGA.
Some of light 106, however, may propagate through the entirety of LGA 110 and may leave LGA 110 through second end 114. This can substantially reduce the efficiency of fixture 100, and limit its desirability. Accordingly, LGA 110 can be modified such that light reaching second end 114 can be turned around and re-directed towards LGA 110.
To improve the efficiency of LGA 300, end 310 can include angled facets 320 and 322 defining a retroreflective element on a trailing edge of the LGA. In particular, facet 320 can extend from end point 321 of upper surface 316 to tip 324, and facet 322 can extend from end point 323 of lower surface 318 to tip 324. Each of facets 320 and 322 can be angled such that tip 324 is farther from the LED module than either end points 321 or 323. In some cases, ends points 321 and 323 can be substantially the same distance from the LED module (e.g., from an end opposite end 310 of LGA 300). End 310 may include a substantially triangular cross-section, where a triangle is defined by ends points 321 and 323 and tip 324.
Although light emitted by a LED module may initially have Lambertian distribution, after propagating through an elongated LGA, the distribution of light may change and become more collimated. In particular, as light is frustrated by LGA 300 and leaves the guide, the remaining light reaching end 310 may be substantially parallel to axis 312 of LGA 300 (e.g., within a plane defined by upper surface 316 or lower surface 318). Facets 320 and 322 can therefore be defined such that light reaching one of the facets along the axis of LGA 300 may be turned around and re-directed back into LGA 300.
Each of facets 320 and 322 can have any suitable angle relative to axis 312. For example, facet 320 can be angled at angle 330 relative to axis 312, and facet 322 can be angled at angle 332 relative to axis 312. Angles 330 and 332 can be selected based on any suitable criteria. In some cases, the angles can be selected to ensure that light reaching a facet will be reflected by the facet due to the critical angle for total reflection corresponding to the index of refraction between the material of LGA 300 and the air in which LGA 300 is placed. For example, angles 330 and 332 can be selected to be larger than 42 degrees when the index of refraction of the LGA/air interface is 1.5. In one implementation, each of angles 330 and 332 is substantially equal to 45 degrees.
Facets 320 and 321 can have any suitable angle relative to one another at tip 324. In some cases, angle 334 at tip 324 can be selected such that light reaching one of facets 320 and 322 can be reflected to the other of the facets, and then back along axis 312 away from end 310. In one implementation, angle 334 can be substantially equal to 90 degrees. Then, light 340 initially reaching facet 320 along axis 312 can be reflected at an angle equal to twice angle 330 towards facet 322 (e.g., 90 degrees if angle 330 is 45 degrees) as light 342, and again reflected at an angle equal to twice angle 332 away from end 310 along axis 312 as light 344 (e.g., 90 degrees if angle 332 is 45 degrees). In particular, facets 320 and 322 can be angled such that the sum of angle 341 between light 340 and 342, and angle 343 between light 342 and 344 is equal to 180 degrees, thus indicating that light is reflected back along axis 312 toward the LED module of the fixture. In some cases, however, light 340 may not be truly collimated, and may therefore retro reflect at an angle other than 180 degrees such that the retroreflected light can encounter a feature of LGA 300 (e.g., a rib) and be frustrated.
Facets 320 and 322 can be constructed using different approaches. In some cases, facets can be cut (e.g., using a machining process), or molded with the LGA. Alternatively, other manufacturing processes can be used to remove material from a LGA and create substantially planar facets. In some cases, the facets can instead or in addition have curved or variable shapes, for example depending on the material used to create the LGA, or on expected angles of incident light in different regions of each facet. In some cases, the surfaces of facets 320 and 322 can be processed to improve their reflectivity. For example, the surfaces of facets 320 and 322 can be polished (e.g., using an abrasive tool). As another example, an external component or coating of a highly reflective material (e.g., a metal) can be applied to the surfaces of facets 320 and 322.
LGA 300 can be constructed from any suitable material. In some cases, the material used can be selected such that the index of refraction between the material and air is approximately 1.5. More generally, the material can be selected such that the index of refraction is in a range that allows for adjacent facets to be angled at 90 degrees relative to one another while ensuring that the angle between an axis of the LGA and each of the facets is more than the critical angle for the index of refraction. Such materials can include, for example, an acrylic, polycarbonate, glass, or another plastic material that is substantially transparent. Using these materials, total internal reflection can be achieved, and therefore improve the efficiency of the LGA without substantially effecting the cost. In some cases, the materials may require a secondary process or cap to ensure total or near total reflection of light within the LGA.
It is to be understood that the steps shown in process 400 of
The above-described embodiments of the invention are presented for purposes of illustration and not of limitation.
