The present invention relates to a light emitting diode (LED) module comprising a substrate having plural indents and flattish portions in between the indents and LEDs mounted in the indents. The present invention also relates to a method for the manufacturing of such an LED module.
An example of an LED module of the above type is disclosed in the document U.S. Pat. No. 6,611,000, wherein plural recesses are formed on a substrate, each recess accommodating an LED. All LEDs are of the same color. A single photodetector is further mounted at the rim of the substrate next to the recesses and LEDs. The LEDs and the photodetector are covered with a transparent resin layer. The function of the single photodetector is to detect an optical output propagating through the transparent resin layer from the LEDs and to feed the output back to control and drive circuits, whereby the output of the LEDs can be adjusted in case the detected output differs from a desired output. Changed LED output can for example be due to changed operating temperature, ageing, etc.
However, a drawback with the LED module in U.S. Pat. No. 6,611,000 is that the single photodetector is most sensitive to the LED it is closest to, which may result in an inaccurate detection and subsequent LED output adjustment. For example, if the LED closest to the photodetector is too low on flux while the other more distant LEDs emits light at a desired flux level, the detection will indicate that the LED output should be increased, even though the overall flux level may be acceptable since the other more distant LEDs emits light at the desired flux level.
It is an object of the present invention to overcome this problem, and to provide an improved LED module allowing more accurate detection of LED characteristics. It is another object of the invention to provide an LED module allowing convenient addition of color.
These and other objects that will be evident from the following description are achieved by means of an LED module, and a method for the manufacturing of such an LED module, according to the appended claims.
According to an aspect of the invention, there is provided an LED module comprising a substrate having plural indents and flattish portions in between the indents, and LEDs mounted in the indents, characterized in that the LED module further comprises at least one sensors and/or at least one additional LED, which are/is provided at the flattish portions.
The invention is based on the understanding that the flattish portions of the substrate between the indents offer a feasible opportunity to place additional components thereat. Placing sensors at the flattish portions allows local detections at various positions of the LED module, which detections can be averaged to a more accurate value compared to a case where a single photodetector at the edge of the substrate is used. Also, since a sensor is placed close to each LED, the LED module can be scaled up to a large size with maintained accurate detection of local LED characteristics. Also, in case LEDs of different colors are used, each color can get its own sensor, which allows for color specific feedback. Further, placing additional LEDs at the flattish portions allows for generation of additional flux as well as compensation of the LED efficacy when temperature is raised during operation. For example red LEDs' output decreases at raised temperature, which can be compensated by providing additional red LEDs. In this way, the amount of red flux can be adjusted to keep homogenous color mixing. At each given flattish portion there can be positioned a sensor only, an additional LED only, both a sensor and an additional LED, or it can be left empty. Thus, various configurations are possible.
The sensors can include flux sensors for measuring the lumen output of the LEDs to provide (local) flux feedback, or temperature sensors for measuring the LEDs' temperature to provide (local) temperature feedback. The flux sensor can for example be a photodiode (filtered or unfiltered), a CMOS-sensor, a CCD, etc. The temperature sensor can for example be an NTC temperature sensor, a PTC temperature sensor or diode junction temperature sensor.
The sensors can be placed on the very top of the flattish portions between the indents, or in recesses in the flattish portions. In the former case, for flux sensors, a shielding is preferably provided around the sensor to insulate the sensor from direct light from the LEDs. Optics placed above the substrate, such as a reflector or collimator, ensures that a sufficient amount of light returns to the sensor for allowing proper detection. In the latter case, the recesses are preferably etched into the flattish portions of the substrate, in this case advantageously a silicon substrate, and sized to partly bury a flux sensor placed in the recess, again to insulate the sensor from direct light from the LEDs. Thus, in the latter case, no additional shielding is necessary. Further, any additional LEDs are preferably mounted on top of the flattish portions, for maximum out coupling of light.
The indents of the substrate are preferably achieved by etching before the various components are mounted to the substrate. Also preferably, the indents of the substrate have sloping side surfaces. The sloping side surfaces can be planar or curved. The sloping side surfaces allow pre-collimation of the light emitted from the LED(s) accommodated in the indent by using the side surface as a reflector. Further, in case plural LEDs are accommodated in the indent, such as a red, green and blue LED, the sloping side surfaces also serve to pre-mix the light emitted from the different LEDs, i.e. the indent functions as a color-mixing chamber.
According to another aspect of the invention, there is provided a method for the manufacturing of an LED module, comprising preparing a substrate by etching plural indents into the substrate such that flattish portions are formed in between the indents, mounting LEDs in the indents, and providing at least one of sensors and additional LEDs at the flattish portions. This method offers similar advantages as obtained with the previously discussed aspect of the invention.
This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.
a is a schematic cross-sectional side view of an LED module according to an embodiment of the invention,
b is a schematic top view of the LED module of
a is a schematic cross-sectional side view of an LED module 10 according to an embodiment of the invention. The LED module 10 comprises a pre-etched substrate 12 with a plurality of indents 14. The indents 14 are preferably pre-etched. In each indent 14, there is provided an LED generally designated 16, in this case a red LED 16a, a green LED 16b, and a blue LED 16c. The LEDs can be intrinsic LEDs or phosphor converted LEDs. Each LED 16 is mounted to a bottom surface of the indent 14. The indents 14 have sloping side surfaces 18. The sloping side surfaces 18 in
Between the indents 14, and next to the outer indents, there are formed essentially flat portions 20 onto which sensors generally designated 22 are mounted. The sensors 22 can include flux sensors 22a and/or temperature sensors 22b. The LED module 10 in
Upon operation of the LED module 10, light emitted from an LED 16 is pre-collimated by the sloping side surfaces 18 of the indent 14 in which it is accommodated, as indicated by exemplary ray traces 30. Light emitted from the LEDs 16 propagates through the encapsulant 28 and the optics 26 and is detected by the flux sensors 22a. The optics 26 ensures that a sufficient amount of light returns to the sensor to allow proper detection. In the LED module 10 of
b is a schematic top view of the LED module of
A method for the manufacturing of any of the LED modules of the invention described above is summarized in the flow chart of
The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, an LED module with only additional LEDs at the flattish portions, but no sensors, could be envisaged.
Number | Date | Country | Kind |
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06112437.6 | Apr 2006 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2007/051184 | 4/3/2007 | WO | 00 | 10/9/2008 |