Română English

Correlated Color Temperature Processor for LED Lighting Fixtures and Extended Warranty - PCAI

Research contract funded by UEFISCDI type PN-III-P2-2.1-CI-2018-0965, No. 163CI / 2018

Co-financing: SC GREENTEK LIGHTING SRL București

Project duration: between July 4, 2018 and December 15, 2018.

Report to December 15, 2019

Project team:

  • Phd. Cătălin Daniel Gălățanu, professor at "Gheorghe Asachi" Technical University of Iaşi
  • Phd. Cristian Gyozo Haba, professor at "Gheorghe Asachi" Technical University of Iaşi
  • Phd. Liviu Breniuc, professor at "Gheorghe Asachi" Technical University of Iaşi
  • Phd. Daniel Petrișor, lecturer at "Gheorghe Asachi" Technical University of Iaşi

Results:

  • Number of patent applications filed: 1, at June 2019

Published papers:

  1. Breniuc, Liviu; Haba, Cristian-Gyozo; Gălățanu, Cătălin-Daniel; et al., Correlated Color Temperature Measuring and Adjustment System, 11th International Symposium on Advanced Topics in Electrical Engineering (ATEE),WOS:000475904500083, 2019
  2. Haba, Cristian-Gyozo; Breniuc, Liviu; Gălățanu, Cătălin-Daniel; et al., IoT System for Implementation of Connected Lighting, 11th International Symposium on Advanced Topics in Electrical Engineering (ATEE), WOS:000475904500171, 2019
  3. Haba, Cristian-Gyozo; Breniuc, Liviu; Canale, Laurent; Gălățanu, Cătălin-Daniel, Study on the Influence of Various Factors on Measurement of CCT for a Controlled Lighting System, IEEE Industry Applications Society Annual Meeting, Baltimore, USA, DOI: 10.1109/ IAS.2019.8912313 și urmează indexare WOS, 2019
  4. Gălățanu, Cătălin-Daniel, Improving the Luminance Measurement from Digital Images, International Conference on Electromechanical and Energy Systems (SIELMEN ), DOI: 10.1109/SIELMEN.2019.8905887, și urmează WOS, 2019
  5. Haba, Cristian-Gyozo; Gălățanu, Cătălin-Daniel; Breniuc, Liviu, Reduction of Energy Consumption for Architectural Lighting Systems, 2019 International Conference on Electromechanical and Energy Systems (SIELMEN), DOI: 10.1109/ SIELMEN.2019.8905855 și urmează WOS, 2019

The principle of the CCT measurement method

The measurement of the color temperature can be done by using specialized devices, from the category of spectrometers, whose price makes them to be used on a small scale, and only in the laboratory. The project has developed a method and a means by which the color temperature of lighting sources can be measured using a digital camera. Thus, for sources with variable color temperature (or different sources), various images are first purchased, as in Fig.1:

Fig.1 – The image of sources with different color temperatures

We mention that in Fig.1 the shades are exaggerated and distorted by the non-specific playback chain including the RGB sensor, which has been underexposed, so as not to have saturated images that render the white shade but where the information on CCT is lost. It follows that Fig.1 will be interpreted as white light (RGB = [256, 256, 256]) but underexposed, thus the white light will change from warm CCT (2700 K) to cold white (6500 K).

The calibration method then extracts the pixel values and these values are statistically processed, as in Fig.2:

Fig.2 – Histogram of pixel distribution around values indicating three color temperatures

For specialized color temperature measurements, the RGB to XYZ conversion matrix can be calculated for various types of image sensors.

In addition to the imaging measurement of the CCT, a CCT adjustment system was also made, according to Fig.3, where the composition is also indicated:

Fig.3 – Automatic CCT adjustment system.
1 – Lighting fixture with variable, programmable CCT (GREENTEK LIGHTING)
2 – WF32 microsystem
3 – RS232 adapter
4 – RS232 – DALI adapter
5 – PmodENC encoder
6 – OLED display
7 – RGB sensor TCS34725

With this automatic adjustment system, the CCT adjustment could be performed, according to Fig.4:

Fig.4 –
a) Color temperature measured according to the preset value;
b) Errors in the color temperature control system

In Fig. 4 it is observed that the adjustment is proportional, practically the measured CCT value is identical to the preset CCT, except at the extreme values, where the system no longer makes adjustment. As a principle, variable CCT is obtained from the mixture of two light flux components with extreme CCT, in our case 2700 K and 6500K. The value of 6500K could not be obtained because the LEDs with cold light in the tested device proved to have a CCT of 6200 K.

This principle and system can be used to make lighting fixtures with variable CCT or, in other situations, constant CCT.

The main results:

  • Design and prototype of an integrated system (microprocessor) for color temperature control. It has an interface with the DALI system that is currently used by Greentek.
  • Calibration of a digital camera to measure the color temperature field.
  • Software dedicated to correlated color temperature (CCT) calculation