Method and apparatus for illuminating an object with white light

• US 6,674,060 B2
• Filed: 11/06/2001
• Issued: 01/06/2004
• Est. Priority Date: 11/06/2000
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Antila, Mika
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/985,729
• Publication Number:
  US 20020113192A1
• Time in Patent Office: 791 Days
• Field of Search: 250/205, 250/214.AL, 250/214.R, 250/216, 250/226, 348/223, 348/227, 348/265, 345/7-10, 345/22, 345/24, 345/38, 345/39, 345/82, 345/83, 345/87, 345/88
• US Class Current: 250/205
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/064 by time modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: H04N 17/02 for colour television signals
• CPC Class Codes: H04N 17/04 for receivers
• CPC Class Codes: H04N 9/73 Colour balance circuits, e.g. white balance circuits or colour temperature control camera processing pipelines for colour balance H04N23/88
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/22 using optical feedback

Abstract

A method and apparatus for illuminating an object with white light, in which method the object is illuminated using lights of at least two different colors. The intensities of the lights are measured and then the intensity of illumination provided by means of a light of a single color is adjusted on the basis of the measured intensities of illumination provided by means of at least two different colors to improve the white balance of the object'"'"'s illumination.

Claims

1. A method for producing white light for illuminating an object, in which method light of a first colour having a first luminous power and light of a second colour having a second luminous power are produced to illuminate the object, wherein the method comprises the steps of:

measuring the first luminous power;

measuring the second luminous power; and

adjusting the white balance of the object'"'"'s illumination by adjusting the first or the second luminous power on the basis of the measured luminous powers of the lights of the first and second colours, wherein the adjustment of the first luminous power comprises the sub-steps of;

intermitting the producing of the light of the first colour so that it is on for only a proportion of the time the object is being illuminated; and

adjusting said proportion to adjust the first luminous power.

2. A method according to claim 1, wherein lights of at least three different colours are produced for illuminating the object.

3. A method according to claim 2, wherein the white balance of the object'"'"'s ambient light is also measured and the luminous power of light of at least one colour to be produced is adjusted in relation to at least one of the other luminous powers to make the luminous power correspond better to the measured white balance of ambient light.

14. A method according to claim 1, wherein the adjustment of the second luminous power comprises intermitting the producing of the light of the second colour.

15. A method according to claim 1, wherein the repeated interrupting of the illumination corresponds to a Pulse Width Modulated signal.

16. A method according to claim 1, wherein the object is a display.

17. A method according to claim 1, wherein the white balance of the object'"'"'s ambient light is measured intermittently on instants of time when the producing of the light of the first colour is interrupted and said proportion is adjusted in accordance with the measured white balance of ambient light.

18. A method according to claim 1, wherein the intermitting takes place so that the illumination appears non-flickering.

4. An apparatus for illuminating an object with white light, the apparatus comprising:

first illuminating means for producing light of a first colour having a first luminous power;

second illuminating means for producing a light of a second colour having a second luminous power;

means for measuring the first luminous power;

means for measuring the second luminous power; and

means for adjusting the white balance of the object'"'"'s illumination by adjusting the first or second luminous power on the basis of the measured first and second luminous powers, wherein the adjusting the first luminous power comprises intermitting the producing of the light of the first colour so that it is on for only a proportion of the time the object is being illuminated and adjusting the proportion to adjust the first luminous power.

5. An apparatus according to claim 4, the apparatus further comprising

means for measuring the white balance of the object'"'"'s ambient light; and

means for adjusting at least one luminous power in relation to the measured white balance of ambient light.

6. An apparatus according to claim 4, the apparatus also comprising at least partially common processing means for alternately measuring the different luminous powers.

7. An apparatus according to claim 4, the apparatus being arranged to iteratively adjust the white balance of the object'"'"'s illumination during illumination.

8. An apparatus according to claim 4, the apparatus being arranged to apply a first measurement unit to measure the luminous power of light of a first colour in a significantly normalised illumination with regard to the light in question to determine at least one individual measurement unit characteristic and to use it for correcting a later measurement.

9. An apparatus according to claim 4, wherein the object to be illuminated is a display for visual presentation of information.

10. An apparatus according to claim 9, wherein the means for measuring the first luminous power and the means for measuring the second luminous power are arranged in the vicinity of the display.

11. An apparatus according to claim 9, wherein a portion of the display is arranged to serve at least occasionally as the means for measuring the at least one luminous power.

12. An apparatus according to claim 4, wherein at least one set of illuminating means is arranged to intermit light according to a PWM-modulated (Pulse Width Modulation) signal.

13. An apparatus according to claim 4, the apparatus being selected from a group comprising the following alternatives:

mobile station, electronic camera, electronic video camera, electronic book, portable computer, display with back illumination, display with front illumination, and an illuminating device for a work of art.

19. An apparatus according to claim 4, wherein the frequency of the intermitting is high enough to make the illuminating appear flicker free.

20. An apparatus according to claim 4, comprising means for adapting the illuminating according to ambient light white balance configured to use the means for measuring the first luminous power on instants when the means for producing a light of the first colour have been interrupted.