Flat lighting source, luminance correcting circuit, luminance correcting method and liquid crystal display

Abstract

A flat lighting source is provided which is capable of applying illuminating light to an entire display region of a display panel. A current or voltage is supplied from each LED (Light Emitting Diode) driving/correcting circuit to each LED. Part of light emitted from each of the LEDs is converted into electrical signals and a resistance value of each photodiode decreases in proportion to luminance. If luminance of light emitted from each of the LEDs increases, a resistance value of each of the photodiodes decreases while the luminance of light emitted from each of the LEDs decreases. The resistance value is fed back to each of the LED driving/correcting circuits which changes a driving current or a driving voltage so that luminance of light emitted from each of the LEDs corresponds to a luminance setting voltage. The photodiode is mounted in a one-to-one relationship for every LED.

1 . A flat lighting source having a plurality of light emitting devices so arranged as to form a planar surface and letting illuminating light come in a display region of a transmissive-type display panel from its rear, comprising: 
 a plurality of luminance correcting circuits each to set luminance of light to be emitted from each of said plurality of light emitting devices at a targeted value for every light emitting device and to detect an amount of deviation in luminance of light from said targeted value occurring when each of said plurality of light emitting devices is turned ON, and to make said luminance of light coincide with said targeted value, based on the detected amount of deviation.    
   
   
       2 . The flat lighting source according to  claim 1 , wherein said luminance correcting circuit comprises: 
 a plurality of photo-detecting devices so mounted as to correspond to each of said plurality of light emitting devices in a one-to-one relationship which receives light emitted from each of said plurality of light emitting device and generates a luminance detecting signal having a level corresponding to luminance of light emitted from each of said plurality of light emitting devices; and    a plurality of driving/correcting circuits each being mounted so as to correspond to each of said plurality of light emitting devices in a one-to-one relationship, each of which supplies driving power to each of said plurality of light emitting devices and detects deviation in luminance of light emitted from each of said plurality of light emitting devices from a targeted value, based on a level of said luminance detecting signal, and corrects said driving power so that said deviation is compensated for.    
   
   
       3 . The flat lighting source according to  claim 2 , wherein each of said plurality of said photo-detecting devices is arranged, in a one-to-one relationship, in a vicinity of each of said plurality of said light emitting devices.  
   
   
       4 . The flat lighting source according to  claim 3 , wherein said plurality of light emitting devices and said plurality of photo-detecting devices are mounted together in a same package.  
   
   
       5 . A luminance correcting circuit to be used in a flat lighting source having a plurality of light emitting devices so arranged as to form a planar surface and letting illuminating light come in a display region of a transmissive-type display panel from its rear, wherein each of said luminance correcting circuits sets luminance of light to be emitted from each of said plurality of light emitting devices at a targeted value for every light emitting device and detects an amount of deviation in luminance of light from said targeted value occurring when each of said plurality of light emitting devices is turned ON, and makes said luminance of light coincide with said targeted value based on the detected amount of deviation.  
   
   
       6 . The luminance correcting circuit according to  claim 5 , further comprising: 
 a plurality of photo-detecting devices each being mounted so as to correspond to each of said plurality of light emitting devices in a one-to-one relationship and to receive light emitted from each of said plurality of light emitting devices; and    a plurality of driving/correcting circuits each being mounted so as to correspond to each of said plurality of light emitting devices in a one-to-one relationship and to supply driving power to each of said plurality of light emitting devices and to detect deviation in luminance of light emitted from each of said plurality of light emitting devices from a targeted value, based on a level of said luminance detecting signal, and to correct said driving power so that said deviation is compensated for.    
   
   
       7 . A luminance correcting method to be applied to a flat lighting source having a plurality of light emitting devices so arranged as to form a planar surface and letting illuminating light come in a display region of a transmissive-type display panel from its rear, comprising; 
 setting luminance of light to be emitted from each of said plurality of light emitting devices at a targeted value for every light emitting device;    detecting an amount of deviation in luminance of light from said targeted value occurring when each of said plurality of light emitting devices is turned ON; and    making said luminance of light coincide with said targeted value based on the detected amount of deviation.    
   
   
       8 . A flat lighting source comprising: 
 a plurality of light emitting devices;    a plurality of luminance detecting devices, each of which is provided, in a one-to-one relationship with each of said plurality of said light emitting devices, to receive light emitted from the corresponding light emitting device; and    a plurality of luminance correcting circuits, each of which is provided, in a one-to-one relationship with each of said plurality of said light emitting devices, to correct luminance of light emitted from the corresponding light emitting devices, based on a difference between a predetermined desirable luminance value and a detected luminance value obtained from the corresponding luminance detecting device, so as to maintain uniformity of the luminance of each of said light emitting devices.    
   
   
       9 . The flat lighting source according to  claim 8 , wherein said light emitting devices each comprise a light emitting diode.  
   
   
       10 . A liquid crystal display provided with a flat lighting source for backlighting, 
 the flat lighting source comprising:    a plurality of light emitting devices;    a plurality of luminance detecting devices, each of which is provided, in a one-to-one relationship with each of said plurality of said light emitting devices, to receive light emitted from the corresponding light emitting device; and    a plurality of luminance correcting circuits, each of which is provided, in a one-to-one relationship with each of said plurality of said light emitting devices, to correct luminance of light emitted from the corresponding light emitting devices, based on a difference between a predetermined desirable luminance value and a detected luminance value obtained from the corresponding luminance detecting device, so as to maintain uniformity of the luminance of each of said light emitting devices.    
   
   
       11 . The liquid crystal display according to  claim 10 , wherein said light emitting devices each comprise a light emitting diode.