Video lighthead with dimmer control and stabilized intensity

• US 5,994,844 A
• Filed: 12/12/1997
• Issued: 11/30/1999
• Est. Priority Date: 12/12/1997
• Status: Expired due to Fees

• Current Assignee: Frezzolini Electronics Incorporated
• Original Assignee: Frezzolini Electronics Incorporated
• Inventors: Crawford, Kevin J., Crawford, James J.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Lee, Wilson
• Application Number:
  US08/989,923
• Time in Patent Office: 718 Days
• Field of Search: 315/149, 315/151, 315/150, 315/152, 315/155, 315/158, 315/297, 315/153, 315/307, 315/362, 315/DIG. 4, 315/208, 315/224, 362/4, 362/5, 362/18, 362/276
• US Class Current: 315/151
• CPC Class Codes: G03B 15/02 Illuminating scene
• CPC Class Codes: H05B 39/042 by measuring the incident light
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps

Abstract

A video lighthead mountable to a video camera and having a dimmer control that varies the intensity of the light output from the lighthead using pulse width modulation techniques. A photo sensor measures the intensity of light reflected from a subject in front of the lighthead. The intensity of light output from the lighthead is adjusted by control circuitry in response to changes in measured reflected light intensity to maintain a constant level of illumination. The adjustment is carried out by modifying the duty cycle of a pulse width modulation circuit. The duty cycle adjustment of the pulse width modulation is also used to compensate for supply voltage variations in order to maintain constant light output.

Claims

1. A video lighthead comprising:

a lighthead having a housing;

a light source located in said housing;

a pulse width modulation circuit for controlling said light source, wherein the brightness of said light is determined by the duty cycle of said pulse width modulation circuit;

a photo-sensor for measuring the intensity of light reflected from an object in front of said light source;

means for automatically adjusting said duty cycle in response to the measured intensity of reflected light;

a memory device for storing a first reflected light intensity value;

a comparator for comparing said first stored intensity value with a second reflected light intensity value, said comparator outputting a comparison value to said means for automatically adjusting in order to adjust said duty cycle so that said second reflected light intensity value is made substantially equal to said first stored intensity value;

a means for deactivating said light when the suply voltage is less than a predefined minimum value;

and a means for manually adjusting said duty cycle.

4. The lighthead of claim 1, wherein said means for automatically adjusting said duty cycle adjusts said duty cycle in response to a change in the brightness of said light to thereby maintain a constant light brightness as a voltage supplied by a battery driving said light changes over time.

2. A video lighthead comprising:

a lighthead having a housing;

a light source located in said housing;

a pulse width modulation circuit for controlling said light source, wherein the brightness of said light is determined by the duty cycle of said pulse width modulation circuit;

a photo-sensor for measuring the intensity of light reflected from an object in front of said light source;

means for automatically adjusting said duty cycle in response to the measured intensity of reflected light;

means for manually adjusting said duty cycle;

a memory device for storing the reflected light intensity value;

a comparator for comparing said first stored intensity value with a second reflected light intensity value, said comparator outputting a comparison value to said means for automatically adjusting in order to adjust said duty cycle so that said second reflected light intensity value is made substantially equal to the first stored intensity value;

and a means for deactivating said light when the supply voltage is less than a predefined minimum value.

3. The lighthead of claim 2, further comprising a switch which toggles said lamphead between an automatic adjustment mode and a manual adjustment mode.

5. A video lighthead comprising:

a lighthead having a housing;

a light source located in said housing;

a pulse width modulation circuit for controlling said light source, wherein the brightness of said light is determined by the duty cycle of said pulse width modulation circuit;

a photo-sensor for measuring the intensity of light reflected from an object in front of said light source;

means for automatically adjusting said duty cycle in response to the measured intensity of reflected light;

means for comparing the magnitude of a supply voltage driving said light with a predefined minimum value;

means for deactivating said light when said supply voltage is less than said predefined minimum value;

a memory device for storing a first reflected light intensity value;

a comparator for comparing said first stored intensity value with a second reflected light intensity value, said comparator outputting a comparison value to the means for automatically adjusting in order to adjust said duty cycle so that said second reflected light intensity value is made substantially equal to the first stored intensity value;

and a means for manually adjusting said duty cycle.

6. A method for automatically adjusting the intensity of light emitted by a lighthead comprising the steps of:

(a) providing a pulse-width modulated light source with a controllable duty cycle;

(b) retrieving a preset duty cycles;

(c) setting the controllable duty cycle to said retrieved preset duty cycle;

(d) measuring a first reflected light intensity from an object in front of said light source;

(e) measuring a second reflected light intensity from said object in front of said light source;

(f) comparing said measured second reflected light intensity with said measured first reflected intensity to produce a comparison signal;

(g) adjusting said duty cycle in response to said comparison signal;

(h) repeating steps (f) and (g) until said measured second reflected light intensity substantially equals said measured first reflected intensity; and

the method further comprising the steps of;

measuring the voltage applied to said light source;

comparing said measured voltage to a predefined minimum value; and

deactivating said light source if said measured voltage is less than or equal to said predefined minimum value.

7. A method for automatically adjusting the intensity of light emitted by a lighthead comprising the steps of:

(a) providing a pulse-width modulated light source with a controllable duty cycle;

(b) measuring a first reflected light intensity from an object in front of said light source;

(c) measuring a second reflected light intensity from said object in front of said light source;

(d) comparing said measured second reflected light intensity with said measured first reflected light intensity to produce a comparison signal;

(e) adjusting said duty cycle in response to said comparison signal; and

(f) repeating steps (d) and (e) until said measured second reflected light intensity substantially equals said measured first reflected light intensity;

the method further comprising the steps of;

measuring the voltage applied to said light source;

comparing said measured voltage to a predefined minimum value; and

deactivating said light source if said measured voltage is less than or equal to said predefined minimum value.