Ambient light detector, light source lighting controlling device, and reader

• US 5,932,861 A
• Filed: 10/31/1995
• Issued: 08/03/1999
• Est. Priority Date: 11/01/1994
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Sato, Shinichi, Iwaguchi, Isao, Shinoda, Ichiro
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): Rodriguez, Douglas X.
• Application Number:
  US08/550,839
• Time in Patent Office: 1,372 Days
• Field of Search: 235/455, 235/462, 235/472, 235/462.06, 235/462.39, 235/472.01
• US Class Current: 235/455
• CPC Class Codes: G06K 7/10584 Source control

Abstract

The present invention relates to an ambient light detector that detects a change in light amount of ambient light. The ambient light detector consists of ambient light detecting means for detecting light entering from circumferences and outputting an electrical signal corresponding to the light amount thereof; amplifying means for amplifying the output from the ambient light detecting means; signal producing means for producing a slice level signal based on the output from the amplifying means; comparing means for comparing the output of the amplifying means with the slice level signal; and judging means for judging the level of the output from the amplifying means and then outputting a control signal to control the amplifying factor of the amplifying means, according to the judging result. Ambient light can be stably detected without depending on installation mode or external environment.

Claims

1. An ambient light detector, for a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

ambient light detecting means for detecting a level of the ambient light entering from the circumferences and then outputting a detection signal corresponding to the level of the ambient light;

amplifying means for amplifying said detection signal output from said ambient light detecting means;

judging means for evaluating the level of the output from said amplifying means and then outputting a feedback control signal to control the amplifying factor of said amplifying means according to the evaluation result if the level of the output from said amplifying means is outside of an appropriate range acceptable for subsequent signal processing;

signal producing means for producing a slice level signal based on the resultant output from said amplifying means as controlled by said judging means; and

comparing means for comparing said resultant level of output of said amplifying means, which output is received from said amplifying means and is the result of the feedback of said judging means, with the slice level signal produced by said signal producing means and then outputting a control signal corresponding to the comparison result to control the system.

2. An ambient light detector according to claim 1, wherein said amplifying means is an amplifying-factor-variable amplifier, and wherein said judging means includes a first comparator for comparing the level of the output of said amplifying means with a first reference value and then outputting a first control signal according to the comparison result to control the operation of said amplifier, and a second comparator for comparing the level of the output of said amplifier with a second reference value different from said first reference value and then outputting a second control signal according to the comparison result to control the operation of said variable amplifier.

3. An ambient light detector, for a system in which a change of state of an ambient is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

ambient light detecting means for detecting a level of the ambient light entering from the circumferences and then outputting a detection signal corresponding to the level of the ambient light;

amplifying means for amplifying the detection signal output from said ambient light detecting means;

signal producing means for producing a slice level signal based on the level of the output of said amplifying means;

judging means for evaluating the level of the output from said amplifying means and then outputting a control signal to control the level of said slice level signal to be outputted from said signal producing means according to the evaluation result if the level of the output from said amplifying means is outside of an appropriate range acceptable for subsequent signal processing; and

comparing means for comparing said level of the output of said amplifying means, which output is received from said amplifying means, with said slice level signal output from said signal producing means and then outputting a control signal corresponding to the comparison result to control the system.

4. An ambient light detector according to claim 3, wherein said signal producing means is a voltage divider for dividing the output from said amplifying means according to a voltage division ratio to output a slice level signal, said voltage division ratio being of said voltage divider being variable according to the control signal output from said judging means, said voltage divider including first and second resistors, a third resistor connected in parallel to said second resistor, and an analog switch connected in series to said third resistor for control the on/off connection state of said third resistor with respect to said first and second resistor so that said voltage division ratio may be determined by said first and second resistors when said analog switch is turned off or by said first, second and third resistors when said analog switch is turned on, and

wherein said judging means including a maximum value updating circuit connected to the output of said amplifying means for updating and storing a maximum level value of the output of said amplifying means, a minimum value updating circuit connected to the output of said amplifying means parallel to said maximum value updating circuit for updating and storing a minimum level value of the output of said amplifying means, a differential amplifier connected respectively to the outputs of said maximum and minimum value updating circuits for operating the differential between the maximum level value of the output of said amplifying means, which output has been updated and stored in said maximum value updating circuit, and the minimum level value of the output of said amplifying means, which output has been updated and stored in said minimum value updating circuit, and a comparator connected to the output of said differential amplifier for comparing said differential between the maximum and minimum level values, which differential has been operated by said differential amplifier, with a predetermined threshold and outputting a control signal to selectively turn on or off said analog switch when said differential value is smaller or larger than said threshold, and vice versa.

5. An ambient light detector, for a system in which a change of an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

ambient light detecting means for detecting a level of the ambient light entering from the circumferences and then outputting a detection signal corresponding to the level of the ambient light;

amplifying means for amplifying the detection signal output from said ambient light detecting means;

signal producing means for producing a slice level signal based on the output of said amplifying means, said signal producing means being in the form of a voltage divider for dividing the output of said amplifying means according to a voltage division ratio to output a slice level signal;

comparing means for comparing the level of the output of said amplifying means, which output is received from said amplifying means, with said slice level signal output from said signal producing means and then outputting a signal corresponding to the result; and

time measuring means for starting a time-measuring operation when a power source is switched on and then outputting a control signal after a lapse of a predetermined period of time to said voltage divider to control the level of said slice level signal, said time measuring means being adapted to be reset according to the comparison result from said comparing means.

6. An ambient light detector, for a system in which a change of state of an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

ambient light detecting means for detecting a level of the ambient light entering from circumferences and outputting a detection signal corresponding to the light amount thereof;

control means for outputting a predetermined slice level signal;

comparing means for comparing the level of said detection signal output from said ambient light detector with said slice level signal produced by said control means and then outputting a signal corresponding to the result; and

switching means for switching the operational status of said control means;

said control means being adapted to store the level of said electrical signal output from said ambient light detecting means when the operational status is switched by an operation of said switching means and then producing a slice level signal based on the level of said electrical signal stored.

7. An ambient light detector comprising:

ambient light detecting means for detecting light entering from circumferences and outputting an electrical signal corresponding to the light amount thereof;

control means for outputting a predetermined slice level signal;

comparing means for comparing said electrical signal with said slice level signal and then outputting a signal corresponding to the result; and

switching means for switching the operational status of said control means;

said control means storing the level of said electrical signal sent from said ambient light detecting means when the operational status is switched by an operation of said switching means and then producing a slice level signal based on the level of said electrical signal stored, wherein said control means stores said electrical signal from said ambient light detecting means in the form of a digital signal and then outputs a slice level signal in the form of a digital signal and wherein said control means comprises analog to digital converting means for converting an output signal from said ambient light detecting means into a digital signal and then outputting the result to said control means, and digital to analog converting means for converting a digital slice level signal sent from said control means into an analog slice level signal and then outputting the result to said comparing means.

8. An ambient light detector, for a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

ambient light detecting means for detecting a level of the ambient light entering from circumferences and then outputting an analog detection signal corresponding to the level of the ambient light;

amplifying means for amplifying the detection signal output from said ambient light detecting means;

an analog to digital converter for converting said analog detection signal output, as amplified by said amplifying means, into selectively a digital signal in a normal level or in an expanded level larger than the normal level if said analog detection signal output is off an appropriate range acceptable for subsequent signal processing; and

control means for comparing the level of said digital signal from said analog to digital converter with a predetermined reference value and then outputting a range select switch signal according to the comparison result to switch the range of said analog to digital converter to a suitable range and to vary the level of said digital signal from analog to digital signal and to control the lighting of the system.

9. An ambient light detector, for a system in which a change in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of operation of the system irrespective of the irregularity of the ambient light change, said detector comprising:

a plurality of ambient light detectors each for detecting a level of the ambient light entering from circumferences and then outputting a detection signal corresponding to the level of the ambient light and different in level from that output from another ambient light detector;

switching means connected to each of said plurality of ambient light detectors, for validating the operation of one of said ambient light detectors at a time; and

control means for comparing said detection signal output from one in operation among said plural ambient light detectors, which output is received from said selected ambient light detector, with a predetermined reference value and then outputting a control signal according to the comparison result to control the on/off operation of said switching means, in such a way that one of said ambient light detectors may be selected for operation.

10. A light source lighting controlling device for controlling lighting of a light source in a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said device comprising:

an ambient light detector for detecting a level of the ambient light entering from circumferences and then outputting a detection signal corresponding to the level of the ambient light;

amplifying means for amplifying the output from said ambient light detector;

signal producing means for producing a slice level signal based on the output from said amplifying means;

judging means for evaluating the level of the output from said amplifying means and then outputting a control signal to control the amplifying factor of said amplifier in accordance with the evaluation result if the level of the output from said amplifying means is outside of an appropriate range acceptable for subsequent signal processing;

comparing means for comparing the output of said amplifying means, which output is received from said amplifying means, with said slice level signal and then outputting a signal according to the comparison result; and

light source drive circuit for controlling the lighting status of the light source according to said signal output from said comparing means.

11. A light source lighting controlling device according to claim 10, wherein said amplifying means is a multiplying-factor-variable amplifier, and wherein said judging means includes a first comparator for comparing the level of the output of said amplifying means with a first reference value and then outputting a first control signal to control the operation of said amplifier, and a second comparator for comparing the level of the output of said amplifier with a second reference value different from said first reference value and then outputting a second switching signal to control the operation of said amplifier.

12. A light source lighting controlling device for controlling lighting of a light source of a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said device comprising:

ambient light detecting means for detecting a level of the ambient light entering from circumferences and then outputting a detection signal corresponding to the level of the ambient light;

signal producing means for producing a slice level signal based on the output of said ambient light detecting means;

judging means for evaluating the output from said ambient light detecting means and then outputting a control signal to control the level of said slice signal output from said signal producing means according to the evaluation result if the level of the output from said ambient light detecting means is off and appropriate range acceptable for subsequent signal processing;

comparing means for comparing said resultant level of the output of said ambient detecting means, which output is the result of the feedback of said judging means, with said slice level signal produced by said signal producing means and then outputting a signal according to the comparison result; and

a light source drive circuit for controlling the lighting status of the light source in accordance with said signal output from said comparing means.

13. A light source lighting controlling device according to claim 12, wherein said signal producing means is a voltage divider for dividing the output from said ambient light detecting means in accordance with a varying voltage division ratio to output a slice level signal, said voltage division ratio being of said voltage divider being variable according to the control signal output from said judging means, said voltage divider including first and second resistors, a third resistor connected in parallel to said second resistor, and an analog switch connected in series to said third resistor for control the on/off connection state of said third resistor with respect to said first and second resistor so that said voltage division ratio may be determined by said first and second resistors when said analog switch is turned off or by said first, second and third resistors when said analog switch is turned on, and

wherein said judging means including a maximum value updating circuit connected to the output of said judging means for updating and storing a maximum level value of the output of said amplifying means, a minimum value updating circuit connected to the output of said amplifying means parallel to said maximum value updating circuit for updating and storing a minimum level value of the output of said amplifying means, a differential amplifier connected respectively to the outputs of said maximum and minimum value updating circuits for operating the differential between the maximum level value of the output of said amplifying means, which output has been updated and stored in said maximum value updating circuit, and the minimum level value of the output of said amplifying means, which output has been updated and stored in said minimum value updating circuit, and a comparator connected to the output of said differential amplifier for comparing said differential between the maximum and minimum level values, which differential has been operated by said differential amplifier, with a predetermined threshold and outputting a control signal to selectively turn on or off said analog switch when said differential value is smaller or larger than said threshold, and vice versa.

14. A light source lighting controlling device for controlling light of a light source of a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said device comprising:

ambient light detecting means for detecting a level of the ambient light entering from the circumferences and then outputting a detection signal corresponding to the level of the ambient light;

signal producing means for producing a slice level signal based on the output of said amplifying means, said signal producing means being in the form of a voltage divider for dividing the output of said amplifying means according to a voltage division ratio to output a slice level signal;

time measuring means for starting a time-measuring operation when a power source is switched on and then outputting a control signal after a lapse of a predetermined period of time to said voltage divider to control the level of said slice level signal;

comparing means for comparing the level of the output of said amplifying means, which output is received from said amplifying means, with said slice level signal output from said signal producing means and then outputting a signal corresponding to the comparison result; and

light source drive means for performing lighting control of the light source in accordance with said signal output from said comparing means;

said time measuring means being adapted to be reset according to the comparison result from said comparing means.

15. A light source lighting controlling device for controlling light of a light source of a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said device comprising:

ambient light detecting means for detecting a level of the ambient light entering from circumferences and outputting detection signal corresponding to the level of the ambient light;

control means for outputting a predetermined slice level signal;

comparing means for comparing the level of the output of said ambient light detecting means with said slice level signal produced by said control means and then outputting a control signal corresponding to the comparison result;

light source drive means for performing lighting control of said light source in accordance with said control signal; and

switching means for switching the operational status of said control means;

said control means adapted to store the level of said electrical signal sent from said ambient light detecting means based on the operational status switched due to an operation of said switching means and outputs a slice level signal based on the level of said electrical signal stored.

16. A light source lighting controlling device which includes a light source and turns controllably on and off said light source, comprising:

ambient light detecting means for detecting light entering from circumferences and outputting an electrical signal corresponding to the light amount thereof;

control means for outputting a predetermined slice level signal;

comparing means for comparing said electrical signal with said slice level signal and then outputting a control signal corresponding to the result;

light source drive means for performing lighting control of said light source in accordance with said control signal; and

switching means for switching the operational status of said control means;

said control means storing the level of said electrical signal sent from said ambient light detecting means based on the operational status switched due to an operation of said switching means and outputs a slice level signal based on the level of said electrical signal stored, said light controlling device further comprising

analog to digital converting means for converting an output signal from said ambient light detecting device into a digital signal and then outputting the result to said control means, and digital to analog converting means for converting a digital slice level signal sent from said control means into an analog slice level signal and then outputting the result to said comparing means; and

wherein said control means stores an electrical signal from said ambient light detecting means in the form of a digital signal and outputs a slice level signal in the form of a digital signal.

17. A light source lighting controlling device, for controlling lighting of a light source of a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said device comprising:

an ambient light detector for detecting a level of the ambient light entering from the circumferences and then outputting an analog detection signal corresponding to the level of the ambient light;

an analog to digital converter for converting said analog detection signal output from said ambient light detector into a digital signal;

control means for comparing said digital signal output from said analog to digital converter with a reference value and then outputting a control signal according to the comparison result, said control means being adapted for evaluating the level of said digital signal from said analog to digital converter and then outputting a switch signal to switch the range of said analog to digital converter when said digital signal is larger than a predetermined upper limit value or smaller than a predetermined lower limit value; and

light source drive means for controlling the lighting status of the light source in accordance with said control signal output from said control means.

18. A light source lighting controlling device, for controlling lighting of a light source of a system in which a change of state in an ambient environment is detected in terms of a change of ambient light entering from circumferences, the ambient light change tending to vary irregularly, and in which such detection result is utilized as a base on which a discrimination is to be made for stable control of lighting of the light source irrespective of the irregularity of the ambient light change, said detector comprising:

a plurality of ambient light detectors each for detecting a level of the ambient light entering from circumferences and then outputting a detection signal corresponding to the level of the ambient light and different in level from that output from another ambient light detector;

switching means connected to each of said plural ambient light detectors, for validating the operation of one of said plural ambient light detectors at a time;

control means for comparing said detection signal output from one in operation among said plural ambient light detectors, which output is received from said selected ambient light detector, with a predetermined reference value and then outputting a control signal according to the comparison result to control the on/off operation of said switching means, in such a way that one of said ambient light detectors may be selected for operation, if the level of said detection signal output is off an appropriate range acceptable for subsequent signal processing; and

light source drive means for controlling the lighting of the light source according to said control signal output from said control means.

19. A mark reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a light beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly, for the purpose of automatically controlling lighting of the light source irrespective of the irregularity of the ambient light change, said reader comprising:

an ambient light detector for detecting a level of the ambient light entering into the housing through the reading window and then outputting a detection signal corresponding to the level of the ambient light;

an amplifier for amplifying the detection signal output from said ambient light detector;

judging means for evaluating the level of the output from said amplifying means and then outputting a control signal to control the amplifying factor of said amplifying means in accordance with the evaluation result if the level of the output from said amplifying means is outside of an appropriate range acceptable for subsequent signal processing;

a voltage divider for dividing the output from said amplifier according to a voltage division ratio to output a slice level signal, said voltage division ratio being variable according to the control signal output from said judging means;

comparing means for comparing the level of the resultant output of said amplifier, which output is received from said amplifier and the result of the feedback of said judging means, with the output of said slice level signal output from said voltage divider and then outputting a signal according to the comparison result; and

light source drive means for controlling the lighting status of the light source in accordance with said signal output from said comparing means.

20. A mark reader according to claim 19, wherein said amplifying means includes an amplifying-factor-variable amplifier, and said judging means includes a first comparator for comparing the level of the output of said amplifying means with a first reference value and then outputting a first control signal to control the operation of said variable amplifier in one way, and a second comparator for comparing the level of the output of said amplifier with a second reference value different from said first reference value and then outputting a second control signal to control the operation of said variable amplifier in another way.

21. A mark reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a light beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly, for the purpose of automatically controlling the light source in lighting irrespective of the irregularity of the ambient light change, said reader comprising:

an ambient light detector for detecting a level of the ambient light entering into the housing through the reading window and then outputting a detection signal corresponding to the level of the ambient light;

a voltage divider for dividing the output from said ambient light detector according to a voltage division ratio to output a slice level signal;

a judging circuit for evaluating the level of the output from said ambient light detector and then outputting a control signal to control the voltage division ratio of said voltage divider according to the evaluation result if the level of the output from said ambient light detector is outside of an appropriate range acceptable for subsequent signal processing;

a comparator for comparing the output of said ambient light detector with the output of said voltage divider and outputting a signal according to the comparison result; and

a light source drive circuit for controlling the lighting status of the light source in accordance with the signal output from said comparator; and

judging means for judging the level of the output from said ambient light detecting means and then outputting a control signal to control the voltage division ratio of said voltage dividing means, according to the judging result.

22. A mark reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a light beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly for the purpose of automatically controlling the light source in lighting, said reader comprising;

an ambient light detector for detecting a level of the ambient light entering into the housing through the reading window and then outputting a detection signal corresponding to the level of the ambient light;

signal producing means for producing a slice level signal;

comparing means for comparing the level of said detection signal output from said ambient light detector with the level of said slice level signal produced by said signal producing means and then outputting a signal according to the comparison result;

time measuring means for starting a time-measuring operation, when a power source is switched on, and then outputting a control signal, after a lapse of a predetermined period of time, to said signal producing means to control the level of said slice level signal if the level of the detection signal output from said ambient light detector is outside of an appropriate range acceptable for subsequent signal processing, said time measuring means being adapted to be reset upon receipt of said signal output from said comparing means in accordance with the comparison result; and

light source drive means for performing the lighting control of the light source in accordance with the signal output from said comparing means.

23. A reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a light beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly for the purpose of automatically controlling the light source in lighting irrespective of the irregularity of the ambient light change, said reader comprising:

an ambient light detector for detecting a level of the ambient light entering into the housing through the reading window and then outputting a detection signal corresponding to the level of the ambient light;

control means for outputting a predetermined slice level signal;

comparing means for comparing the level of said detection signal output from said ambient light detector with the level of said slice level signal produced by said control means and then outputting a signal according to the comparison result;

light source drive means for performing the lighting control of said light source in accordance with the control signal; and

switching means for switching the operational status of said control means;

said control means being adapted to store the level of a detection signal from said ambient light detecting means when said switching means witches an operational status and also to produce a slice level signal according to the stored level of the detection signal.

24. A reader which includes a light source and light detecting means, wherein a mark formed on an article is read by operationally irradiating light from said light source onto said article and detecting light reflected on said article using light detecting means, comprising:

ambient light detecting means for detecting light entering from circumferences and outputting an electrical signal corresponding to the light amount thereof;

control means for outputting a predetermined slice level signal;

comparing means for comparing said electrical signal with said slice level signal and outputting a signal according to the result;

light source drive means for performing the lighting control of said light source in accordance with the control signal; and

switching means for switching the operational status of said control means;

said control means storing the level of an electrical signal from said ambient light detecting means when said switching means switches an operational status;

said control means producing a slice level signal according to the electrical signal level stored, said reader further comprising

analog to digital converging means for converting an output signal from said ambient light detecting device into a digital signal and then outputting the result to said control means, and digital to analog converting means for converting a digital slice level signal sent from said control means into an analog slice level signal and then outputting the result to said comparing means; and

wherein said control means stores an electrical signal from said ambient light detecting means in the form of a digital signal and producing a slice level signal in the form of a digital signal.

25. A mark reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a light beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly, for the purpose of automatically controlling the light source in lighting irrespective of the irregularity of the ambient light change, said reader comprising:

ambient light detecting means for detecting a level of the ambient light entering into the housing through the reading window and then outputting a detection signal corresponding to the level of the ambient light;

an analog to digital converter for converting said analog detection signal output from said ambient light detector into a digital signal;

control means for comparing said digital signal output from said analog to digital converter with a reference value and then outputting a control signal according to the comparison result, said control means being adapted for evaluating the level of said digital signal from said analog to digital converter and then outputting, if the level of the detection signal of said ambient light detector is off an appropriate range acceptable for subsequent signal processing, a switch signal to switch the range of said analog to digital converter when said digital signal is larger than a predetermined upper limit value or smaller than a predetermined lower limit value; and

light source drive means for controlling the lighting status of the light source according to said control signal output from said control means.

26. A mark reader for reading a mark labeled on an article, when the article is placed over a reading window outside a housing of said reader, by irradiating a beam onto the mark through the reading window from a light source disposed inside the housing and in which such placing of the article over the reading window is detected in terms of a change in ambient light coming into the housing through the reading window from circumferences, the ambient light change tending to vary irregularly, for the purpose of automatically controlling the light source in lighting irrespective of the irregularity of the ambient light change, said reader comprising:

a plurality of ambient light detectors each for detecting a level of the ambient light entering into the housing through the reading window and then outputting an analog detection signal corresponding to the level of the ambient light and different in level from that output from another ambient light detector;

switching means connected to each of said plural ambient light detectors, for validating the operation of one of said plural ambient light detectors at a time;

an analog to digital converter for converting said analog detection signal output from one in operation among said plural ambient light detectors into a digital signal;

control means for comparing said digital signal output from said analog to digital converter with a reference value and then outputting a control signal according to the comparison result, said control means being adapted for evaluating the level of said digital signal from said detection analog to digital converter and then outputting a control signal, when said digital signal is larger than a predetermined upper limit value or smaller than a predetermined lower limit value, to control the on/off operation of said switching means according to said evaluation result, thus selecting one of said ambient light detectors to be operated; and

light source drive means for controlling the lighting status of the light source according to said control signal output from said control means.