Patent Application
20110208489
This disclosure relates to design methods and more specifically to methods of designing optical systems.
This disclosure was devised by paying specific attention to its possible use in designing optical systems for lighting sources such as LED lighting sources.
Design methods are increasingly drawing attention as a key area of technology. For instance, EP-B-I 112 433 claims a method of designing a roller cone drill bit by calculating certain volumes of formation cut by each tooth in the bit and adjusting correspondingly at least one geometric parameter of the design of the bit. EP-B-I 117 894 again claims a method of designing a roller cone bit by adjusting the orientation of at least one tooth on a cone of the bit, recalculating certain ratios and trajectories and adjusting the orientation of the tooth again in accordance with a recalculated value of the tooth.
High-flux light sources such as LEDs constitute a strong source of heat. High efficiency and high reliability of the associated optical system used for shaping the outgoing light beam is a mandatory requirement. In optical systems including lenses operating on a TIR (Total Internal Reflection) approach, a compromise is usually pursued between cost, efficiency and long lifetime.
Different types of optics may be selected to that end.
A first possible selection is glass optics. These have no reliability limitations in respect of high temperatures: glass can come directly into contact with a high temperature light source without being damaged. Glass optics, however, are rather expensive and usually require an additional holder: achieving complex shapes, possibly including legs or similar formations for fixing to the rest of the light module, is generally difficult in glass optics.
A second possible selection is represented by plastics optics. These are cheap and practical, and can be easily incorporated to a single piece performing both an optical function and a self-holding function. However, operating plastics optics at high temperatures may be critical.
A third possible selection is represented by so-called silicon optics. These represent a sort of trade-off between glass and plastics, in that they are more tolerant to high temperatures in comparison to plastics, while being cheaper with respect to glass optics. However, their mechanical properties may be critical (high thermal expansion, difficulties in achieving complex and/or accurate shapes, inability to be glued).
In this scenario, plastics optics represent the preferred choice for those lighting modules intended to be manufactured in high quantities (high-volume production).
One object of the present invention is to provide inexpensive; high-reliability and compact optical systems including plastics optics while ensuring good reliability and efficiency as a function of the light source characteristics.
This and other objects are attained in accordance with one aspect of the present invention directed to a method of designing an optical system including at least one light source and an optics subjected to aging as a result of exposure to said at least one light source, wherein the method comprises the steps of: defining a thermal aging model for said optics; defining a thermal model for said at least one light source wherein said thermal model is a spatial function representative of the temperature generated by said at least one light source; and defining the distance of said optics from said at least one light source as a function of said aging model and said thermal model.
An embodiment of the arrangement described herein makes it possible to establish an air gap between a high temperature light source (e.g. one or more LEDs) and an associated plastics optics in order to guarantee that the temperature to which the plastics is exposed to does not exceed a defined threshold thus achieving the required lifetime; at the same time, the distance (height) of the lens with respect to the light (and heat) source is optimized in order to avoid that an excessive amount of light escapes the optical system, thus decreasing the overall optical efficiency of the lighting source.
The invention will now be described, by way of example only, by referring to the drawings, wherein:
a and 4b depict the steps of the design method described herein.
In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
In the exemplary embodiment illustrated herein, the light source 10 is a multi-LED light source including e.g. a plurality (e.g. three) LEDs having different emission wavelengths. Such a multi-LED source permits to generate a “white” light having a preselected colour temperature depending on the relative intensities of variation produced by its LED. Also, such an arrangement can be used to produce a coloured radiation.
Reference 20 denotes a reflector which in the multi-LED exemplary embodiment illustrated herein has a corresponding multi-lobed structure, with each lobe playing the role of a respective reflector for one of the light modules in the source 10.
Reference numeral 30 denotes a corresponding plurality of lenses (i.e. an “optics”), again each lens intended to cooperate with a respective one of the LEDs in the source 10. While playing individual roles, the lenses 30 may be either separate independent elements or be integrated to a single piece of plastics material as described herein.
Finally, reference 40 denotes a transparent cover intended to cover the whole arrangement (which is them mounted in an enclosure E whose outline is indicated is broken lines) while permitting propagation of the radiation.
Other than for the design method and details discussed in the following the arrangement illustrated in
Properly designing an optical system as shown in
The flow-chart of
The two parts a) and b) of
In the embodiment considered, three LED modules 100 are arranged in a circular-symmetric positioning layout (e.g. at the vertexes of a triangle). In that way, a minimum and a maximum value for the distance between adjacent LED modules can be determined e.g. as values for the radius of a notional circle over which the LED module are arranged. For instance, RMiN in
Subsequently, starting from the thermal model 206 (see
In an embodiment where plural modules 100 are used, a circular symmetry in the positioning (as shown in
Selecting the minimum value of spacing (i.e. RMiN in
Conversely, selecting the maximum value of spacing (i.e. RMAχ in
Key parameters in reflector design such as dimension and shape and, in the case of multi-polar reflectors, number and characteristics of each individual reflector can be defined as a function of parameters such as:
available space (x, y, z),
light source characteristics, -air-gap dimension,
required viewing angle,
required colour uniformity,
required intensity.
In an embodiment, the plastics optics 30 is developed together with reflector 20 in order to optimise light management. As a function of the plastics optics reliability requirements, the minimum air-gap between the optics lower surface and the light (and heat) source is set as described in the foregoing. Then, according to the optimum minimum air-gap value thus defined, the solid angle of light emission is divided in two zones, namely an external zone for higher angles and an internal zone for smaller angles.
The light rays of the external zone go directly to the reflector 20 while the light rays from the internal zone go to the plastics optics 30 where light is shaped by resorting to a lens-like effect and TIR. Good colour/intensity uniformity can be achieved by “pillows” structures.
Models such as the aging model 204 and the thermal model 206 can be either analytical models or models derived experimentally. In certain embodiments, these models lend themselves to be represented in very simple manner.
For instance, table I below provides an exemplary representation of air-gap dimensioning (step 208 of
Briefly, in Table 1 the aging model 204 corresponds to the indication that, in order to ensure a lifetime of 10 Kh (e.g. 10,000 hours without becoming exceedingly brittle and/or opaque), the temperature of the plastics optics 30 shall never exceed a threshold value of e.g. 1000 C.
Such a model is applicable, for instance, if polycarbonate is selected for the plastics optics 30. The related data can be derived experimentally or may be already provided by the supplier of the material.
The thermal model 206 for the light module (which can be derived by experimental measurements) may indicate e.g. that the temperature in contact with the source is 1300 C and that the temperature at a point P away from the source decreases of 100 C as the distance increases by one millimetre.
This is of course an approximate linear model, provided just for better comprehension of the approach. More generally, the thermal model is a spatial function representative of the temperature generated by the light source 10.
In that way a minimum value DMIN_AIR-GAP of 3 mm is determined for the air gap.
The cover 40 represents an additional component applied to enclose the optical system into the light module enclosure or casing E. Also, the cover 40 can be used for optimizing spot shaping and colour/intensity mixing. In an embodiment, the cover 40 and the optics 30 are integrated to a single piece, thus reducing the costs relating to moulding as well as material and production costs.
The arrangement described herein permits to integrate the reflector 20, the plastics optics 30 and the cover 40 with the following advantages:
cost cutting associated with the use of plastics optics in the place of glass optics for high-flux, high-reliability applications,
optimal definition of air-gap between the optics 30 and the light (and heat) source 10, high optical efficiency achieved by ensuring that all the light rays are properly “captured”, optimum light management in terms of high optical efficiency and light shaping capability in unipolar or multi-polar reflector designs depending on the nature of the source (single or multiple),—the plastics optics 30 and the cover 40 can be integrated to a single piece, thus reducing costs relating to moulding operations and manufacturing components as well as production/assembly complexity and cost. Optical efficiency is also increased due to reduction of the inter-component optical interfaces traversed by the optical radiation.
Of course, without prejudice to the underlying principles of the invention, the details and embodiments may vary, even significantly, with respect to what has been described and illustrated by way of example only, without departing from the scope of the invention as defined by the annexed claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08166835.2 | Oct 2008 | EP | regional |
This is a U.S. national stage of application No. PCT/EP2009/063001, filed on Oct. 7, 2009. This application claims the priority of European application no. 08166835.2 filed Oct. 16, 2008, the entire content of which is hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/063001 | 10/7/2009 | WO | 00 | 4/18/2011 |
