Color measurement instrument with modulated illumination

• US 20030048449A1
• Filed: 05/16/2002
• Published: 03/13/2003
• Est. Priority Date: 05/16/2001
• Status: Active Grant

• Current Assignee: X-Rite Incorporated (Danaher Corporation)
• Original Assignee: X-Rite Incorporated (Danaher Corporation)
• Inventors: Vander Jagt, Peter G., Peterson, Steven H.
• Granted Patent: US 6,888,633 B2
• Time in Patent Office: Days
• US Class Current: 356/432
• CPC Class Codes: G01J 2001/4242 Modulated light, e.g. for synchronizing source and detector circuit
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01J 3/50 using electric radiation detectors
• CPC Class Codes: G01J 3/501 Colorimeters using spectrally-selective light sources, e.g. LEDs
• CPC Class Codes: G01J 3/524 Calibration of colorimeters
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 2201/0625 Modulated LED
• CPC Class Codes: G01N 2201/0627 Use of several LED's for spectral resolution
• CPC Class Codes: G01N 2201/0691 Modulated (not pulsed supply)

Abstract

An instrument and method for measuring light or color using modulated illumination. The system includes an LED illuminator modulated at a specific frequency for illuminating the sample, and a sensor capable of differentiating between the modulated light from the sample and unmodulated ambient light. The instrument is therefore capable of “seeing” only light from the sample, while ignoring ambient light. In a second embodiment, the system includes multiple illuminators of different colors each modulated at a unique frequency so that the sample can be measured at multiple at each of the different frequencies.

Claims

1. A method for measuring optical properties of a sample comprising:

illuminating the sample with modulated light;

detecting light from the sample; and

filtering the detected light to differentiate between modulated detected light and unmodulated detected light.

2. The method of claim 1 wherein said illuminating step includes using an LED.

3. The method of claim 1 wherein the modulated light has a fixed frequency.

4. The method of claim 1 wherein said filtering step includes narrow-band filtering.

5. The method of claim 1 wherein said filtering step includes filtering out infrared light.

6. A method for measuring optical properties of a sample comprising:

illuminating the sample with a plurality of modulated light colors;

detecting light from the sample; and

filtering the detected light to discriminate between modulated detected light and unmodulated detected light.

7. The method of claim 6 wherein said illuminateing step includes modulating each of the light colors at a unique frequency.

8. The method of claim 6 wherein said filtering step includes narrow-band filtering.

9. The method of claim 6 wherein said filtering step includes using a single wide-band sensor.

10. The method of claim 6 wherein said illumination step includes using a square-wave generator.

11. The method of claim 6 wherein said filtering step includes synchronous demodulation.

12. The method of claim 6 wherein said filtering step includes Fourier transformation.

13. An instrument for measuring optical properties of a sample comprising:

means for illuminating the sample with modulated light;

means for detecting light from the sample; and

means for filtering the detected light to differentiate between modulated light from the sample and unmodulated light.

14. The instrument of claim 13 wherein said illuminating means includes an LED.

15. The instrument of claim 13 wherein the modulated light is at a fixed frequency.

16. The instrument of claim 13 wherein said filtering means includes a narrow-band filter.

17. The instrument of claim 13 wherein said filtering means includes an infrared filter.

18. A instrument for measuring optical properties of a sample comprising:

means for illuminating the sample with a plurality of modulated light colors;

means for detecting light from the sample; and

means for filtering the detected light to discriminate between modulated light and unmodulated light.

19. The instrument of claim 18 wherein said illuminating means includes meacns for modulateing each of the light colors at a unique frequency.

20. The instrument of claim 18 wherein said filtering means includes a narrow-band filter.

21. The instrument of claim 18 wherein said filtering means includes using a single wide-band sensor.

22. The instrument of claim 18 wherein said illumination means includes a square-wave generator.

23. The instrument of claim 18 wherein said filtering means includes means for performing a synchronous demodulation.

24. The instrument of claim 18 wherein said filtering means includes means for performing a Fourier transformation.