Image display system with light pen

A display system to display images, comprising:

• a display panel including:
• a first substrate on which first electrodes are formed;
• a second substrate on which a second electrode is formed;
• and
• a liquid crystal layer disposed between the first and second substrates, optical properties of the liquid crystal layer varying in association with changes of electric field formed between the first and second electrodes;
• and
• a data input device interfacing with the display panel using light, the data input device including
• a light converting part receiving image light provided from the display panel, and converting the image light into first sensing light detected by the display panel;
• and
• a detector detecting an amount of the image light arriving at the light converting part, and generating a detect signal in response to the detected amount of the light;
• wherein the light converting part provides a second sensing light to the image display device when the detect signal is less than a reference data.