Liquid crystal display having an improved lighting device

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having at least one light source and projecting light generated by said at least one light source on said liquid crystal display panel;
• and
• a circuit for alternately supplying a lamp current to said at least one light source during a first period t1 and ceasing to supply said lamp current to said at least one light source during a second period t2,
• wherein the following relationship is satisfied:
• first electric power E1 is lower than second power E2, where said first power E1 is defined as (t1×ip-p×Vp-p)/2,
• ip-p=a peak-to-peak value of said lamp current flowing through a respective one of said at least one light source during said first period t1,
• Vp-p=a peak-to-peak value of a voltage across said respective one of said at least one light source during said first period t1,
• said second power E2 is defined as (t1+t2)×(Ieff×Veff),
• Ieff is an effective value of said lamp current flowing through said respective one of said at least one light source during said first period t1 plus and said second period t2, and
• Veff is an effective value of a voltage across said respective one of said at least one light source during said first period t1 plus and said second period t2.

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having at least one light source and projecting light generated by said at least one light source on said liquid crystal display panel;
• and
• a circuit for supplying alternately a first voltage having a first effective value V1 during a first period t1 and a second voltage having a second effective value V2 during a second period t2 to said at least one light source,
• said first voltage producing a first current having a first effective value i1 flowing through said respective one of said at least one light source during said first period t1,
• said second voltage producing a second current having a second effective value i2 flowing through said respective one of said at least one light source during said second period t2,
• said second effective value i2 being smaller than said first effective value i1,
• wherein a first ratio of a first brightness to a first electric power is greater than a second ratio of a second brightness to a second electric power,
• where said first brightness is a brightness produced by said respective one of said at least one light source during said first period t1 plus said second period t2,
• said first electric power is defined as {(t1×V1×i1)+(t2×V2×i2)}/(t1+t2),
• said second electric power is defined as (Veff×ieff)
• Veff is an effective value produced by a combination of said first voltage supplied during said first period t1 and said second voltage supplied during said second period t2,
• ieff is an effective value produced by a combination of said first current flowing during said first period t1 and said second current flowing during said second period t2, and
• said second brightness is a brightness produced by said respective one of said at least one light source supplied with said second electric power.

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having a cold-cathode tube having an end-to-end length L (cm) and projecting light generated by said cold-cathode tube on said liquid crystal display panel;
• and
• a circuit for supplying alternately a first electric power W1 (W) during a first period t1 and a second electric power W2 (W) during a second period t2 to said cold-cathode tube,
• said second electric power W2 being lower than said first power W1,
• wherein a ratio of said first electric power W1 to said end-to-end length L is greater than 0.2 W/cm, and a ratio of said second electric power W2 to said end-to-end length L is equal to or less than 0.1 W/cm.

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having at least one light source and projecting light generated by said at least one light source on said liquid crystal display panel;
• and
• a circuit for supplying alternately a first current having a first effective value i1 during a first period t1 and a second current having a second effective value i2 during a second period t2 to a respective one of said at least one light source,
• said first effective value i1 being greater than a rated value of a lamp current flowing through said respective one of said at least one light source,
• said second effective value i2 being smaller than said rated value of said lamp current,
• wherein said first effective value i1, said second effective value i2, said first period t1 and said second period t2 are selected such that an integral of brightness produced by said respective one of said at least one light source over said first period t1 plus said second period t2 is greater than an integral of brightness produced by said respective one of said at least one light source supplied with said lamp current of said rated value over said first period t1 plus said second period t2.

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having at least one light source and projecting light generated by said at least one light source on said liquid crystal display panel;
• a control circuit configured so as to switch between a first operation and a second operation,
• said first operation supplying a first current having a first effective value i1 during a first period t1 to said at least one light source, and said second operation supplying a second current having a second effective value i2 during a second period t2 to said at least one light source, said second effective value i2 being smaller than said first effective value i1;
• and
• a temperature detector circuit for detecting a temperature of said at least one light source,
• wherein said temperature detector circuit transmits a signal to said control circuit when a temperature of an outside wall of said at least one light source exceeds 65° C., and said control circuit switches from said first operation to said second operation in response to said signal.

A liquid crystal display device comprising:

• a liquid crystal display panel having a plurality of pixels;
• a lighting device having at least one light source and projecting light generated by said at least one light source on said liquid crystal display panel;
• a control circuit configured so as to switch between a first operation and a second operation,
• said first operation supplying a first current having a first effective value i1 during a first period t1 to said at least one light source, and said second operation supplying a second current having a second effective value i2 during a second period t2 to said at least one light source, said second effective value i2 being smaller than said first effective value i1;
• and
• a brightness detector circuit for detecting brightness of said at least one light source,
• wherein said brightness detector circuit transmits a signal to said control circuit when the brightness begins to reduce in said first period t1, and said control circuit switches from said first operation to said second operation in response to said signal.