Discharge gas, surface light source device and backlight unit having the same

A surface light source device comprising:

• a first substrate;
• a second substrate attached to the first substrate to define a discharge space into which a discharge gas is injected, the discharge gas including a mercury gas and an inert gas;
• and
• an electrode for applying a voltage to the discharge gas,
• wherein the inert gas has a pressure of about 10 torr to about 120 torr with respect to a temperature for lighting the discharge gas, and a mixing ratio by weight between the neon gas and the argon gas is about 100:0 to about 40:60.

A backlight unit comprising:

• a surface light source device including a first substrate, a second substrate attached to the first substrate to define a discharge space having an aspect ratio of about 0.07 to about 0.85, and an electrode for applying a voltage to a discharge gas including a mercury gas and an inert gas that is injected into the discharge space, wherein the inert gas has a pressure of about 10 torr to about 120 torr with respect to a temperature for lighting the discharge gas, and a mixing ratio by weight between the neon gas and the argon gas is about 100:0 to about 40:60;
• a case for receiving the surface light source device;
• an optical sheet interposed between the surface light source device and the case;
• and
• an inverter for applying a discharge voltage to the electrode of the surface light source device.