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Optoelectronics/Displays??

Benefits of colour regulation via feedback control

Posted: 25 Jul 2013 ?? ?Print Version ?Bookmark and Share

Keywords:LEDs? temperature? pressure? RGB? colour sensor?

The demonstrated solution differs from the (unregulated) control option by implementing a colour sensor, depending on the lighting concept, to send RGB or other colour values to the micro controller to directly regulate the LED light output. The software of the micro controller compares the given and set values and directs these to the output driver.

Figure 4 demonstrates an RGB system. But this concept works for any LED light source, such as RGB white or RGB amber-white.

What is not demonstrated is how the colour sensor detects the light. Therefore it is useful to generate simple solutions whereas reflecting light can be send to the colour sensor. In other words existing reflectors of manufacturers can be used to achieve this goal at no or hardly any cost increase.

Figure 5: Binning of LEDs by LED manufacturer Luminus.

Figure 6: Visual range within the colour gamut with RGB-LEDs based on colour tolerances (Binning).

Benefits of optical feedback solutions
The LED driver used in can be of simplistic and cost-efficient nature: even a driver without current or LED voltage regulation and without temperature sensor or feedback.

A main issue of the overall savings is the calculation of the total costs as well as future maintenance costs. An additional issue is the question of LED binning. It would be ideal if the light sectors could be directly controlled via the given light output. This would eliminate the requirement of buying from specific bins or just from a single LED manufacturer. Therefore this approach is not only technological beneficial but can also save money during the development planning. It is enough if a LED is within a specific colour segment to later on adjust the overall light output. The consistency of the light will be regulated via feedback control.

If one wants to use the binning segments highlighted in green, the only requirement is to adjust regulation range. The regulation range is usually set to a value of 30% based on ageing- and temperature drift effects, therefore the segment needed to eliminate binning effects is of little importance. But it can save money during the purchasing operation, since tolerance ranges of LED Binnings can be strongly reduced or even eliminated. Often it is hard to buy the same classes/ranges of LEDs at one manufacturer without waiting periods. When taking the availability of specific LED classes into consideration, this can ease the entire purchasing process and limit waiting times until the next class of the same manufacturer is ready.

The visual light colour range is shown in figure 6. The continuous line demonstrates the presentable colour gamut based on all tolerances including the regulation range.

The overall savings potential
In the end of the calculation one needs to recognise the costs benefits and compare. Eliminating negative issues and effects of LEDs such das binning or colour inconstancies as well as creating a long-term stable solutions are just some elements, which can reduce the overall development costs and future running maintenance costs. Therefore it is essential to find the right solution for the given problem and weight the benefits and costs.

The given solution sets itself apart from traditional lighting systems by utilising control options of LED sources, eliminating negative ageing, temperature and light colour shifts, generating long-term stability and reducing potential future maintenance costs. It is important to choose a sensor that does not show ageing-effects itself and is based on the perception of the human eye. The JENCOLOR sensors by MAZeT offer these characteristics.

References
1. MAZeT-Homepage: http://www.mazet.de
2. Color sensor product information: http://www.mazet.de/en/products/jencolor
3. A. Wego, Korrekte Erkennung von Farben und Oberfl?chen mit Farbsensoren, Photonik, 5/2010, pp. 38-42, 2010
4. AVAGO-Homepage (LED aging- characteristics)

About the authors
Fred Grunert and Winfried Mahler are with Mazet GmbH.

To download the PDF version of this article, click here.


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