Illuminant discrimination apparatus and method

• US 4,220,412 A
• Filed: 10/25/1978
• Issued: 09/02/1980
• Est. Priority Date: 10/25/1978
• Status: Expired due to Term

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Martin, William A., Shroyer, Richard A.
• Primary Examiner(s): Hille, Rolf G.
• Application Number:
  US05/954,690
• Time in Patent Office: 678 Days
• Field of Search: 356/218, 356/226, 356/404, 354/31, 354/60 L, 250/226
• US Class Current: 356/218
• CPC Class Codes: G01J 1/42 using electric radiation detectors optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10

Abstract

A method and apparatus for discriminating among various types of illuminants, such as fluorescent light, incandescent light and natural daylight. Such apparatus includes a photoelectric circuit for producing a signal having an amplitude which varies with intensity variations of the illuminant, a bandpass filter circuit having a bandpass centered at the fundamental frequency of the intensity variations of an illuminant energized by an alternating current source, a high-pass filter circuit that passes frequencies higher than such fundamental frequency, a pair of peak detectors for detecting the peak value of signals passed by the first and second filter circuits, and logic circuitry responsive to the outputs of the peak detectors for providing logic outputs indicative of the type of illuminant.

Claims

1. Illuminant discrimination apparatus for discriminating incandescent light from a mixture of daylight and fluorescent light, such incandescent and fluorescent light varying in intensity at a fundamental frequency, said apparatus comprising:

(a) light-sensitive means responsive to incident light for producing a first signal proportional to the instantaneous intensity of said incident light;

(b) circuit means for producing a second signal proportional to the amount of harmonic distortion in said first signal; and

(c) means responsive to said second signal for producing a signal indicative of the type of light incident on said light-sensitive means.

2. The apparatus as defined in claim 1 wherein said circuit means comprises a filter circuit for filtering said fundamental frequency out of said first signal, and a peak detector circuit for detecting the peak value of the filter circuit output.

3. Illuminant discrimination apparatus for detecting which of three types of light, incandescent light, fluorescent light and daylight, is predominant in an illuminated space, such incandescent and fluorescent light being emitted by sources which are periodically energized at a fundamental frequency, said apparatus comprising:

(a) light-sensitive means responsive to incident light for producing a first signal representative of intensity variations in said incident light;

(b) first circuit means, coupled with said light-sensitive means and responsive to said first signal, for producing a second signal representative of the amplitude of said intensity variations occurring at sid fundamental frequency;

(c) second circuit means, coupled with said light-sensitive means and responsive to said first signal, for producing a third signal representative of the amplitude of said intensity variations occurring at frequencies above said fundamental frequency;

(d) logic means, coupled with said first and second circuit means and responsive to said second and third signals, for providing logic outputs indicative of the type of light incident upon said light-sensitive means; and

(e) means, coupled with said logic means and responsive to said logic outputs, for producing a signal indicative of the type of light incident upon said light-sensitive means.

4. The apparatus as defined in claim 3 wherein said light-sensitive means comprises a photovoltaic cell.

5. The apparatus as defined in claim 3 wherein said first circuit means comprises a bandpass filter having a bandpass centered at approximately said fundamental frequency, and a peak detection circuit for providing a signal representative of the peak value of electrical signals passed by said bandpass filter.

6. The apparatus as defined in claim 3 wherein said second circuit means comprises a high-pass filter for filtering out of said first electrical signal frequency components substantially equal to and less than said fundamental frequency, and a peak detection circuit for producing a signal representative of the peak value of signals passed by said high-pass filter.

7. The apparatus as defined in claim 3 wherein said logic means comprises the first threshold sensing means for producing a fourth signal in the event said second signal exceeds a predetermined threshold value, second threshold sensing means for producing a fifth signal in the event said second signal is less than a predetermined threshold value, and a third threshold sensing means for producing a sixth signal in the event the amplitude of said second signal exceeds a predetermined threshold value.

8. The apparatus as defined in claim 7 wherein said logic means further comprises a first NOR gate coupled to said first, second and third threshold sensing means and responsive to the simultaneous absence of said fourth, fifth and sixth signals to produce a seventh signal, and a second NOR gate coupled to said first NOR gate and said second threshold sensing means and responsive to the simultaneous presence of said fifth and seventh signals to produce an eighth signal.

9. A method for discriminating between incandescent-type light and a mixture of daylight and fluorescent-type light, such incandescent-type and fluorescent-type light varying in intensity at a fundamental frequency, said method comprising the steps of:

(a) producing a first signal having an amplitude which varies as a function of light intensity;

(b) detecting the amount of harmonic distortion in said first signal with respect to said fundamental frequency; and

(c) producing a second signal indicative of the type of light based on the amount of harmonic distortion detected.

10. A method for discriminating between incandescent-type light and a mixture of daylight and fluorescent-type light, such incandescent-type and fluorescent-type being emitted by sources which are periodically energized at a fundamental frequency, said method comprising the steps of:

(a) producing a first electrical signal having an amplitude proportional to intensity variations of an unknown illuminant comprising either an incandescent light source of a mixture of fluorescent light and daylight;

(b) filtering said first signal to pass only those eliminate frequency components which are greater than said fundamental frequency;

(c) detecting the peak value of said first signal upon being filtered; and

(d) producing a signal in the event the detected peak value exceeds a predetermined threshold value.