Automatic keypad backlight adjustment on a mobile handheld electronic device

A mobile device, comprising:

• a light sensor;
• a keypad;
• a backlight for the keypad;
• a processor for obtaining light level samples from the light sensor and comparing the light level samples with a first threshold value and a second threshold value;
• and
• a backlight controller for turning the backlight:
• from off to on when a current light level sample is less than the first threshold value below which backlight illumination is used, the first threshold based on a first contrast ratio between light and dark regions of key indicia, and
• from on to off when the current light level sample is greater than the first threshold value but less than the second threshold value based on a second contrast ratio between the light and dark regions of key indicia, the second contrast ratio being less than the first contrast ratio and based on a minimum contrast at which the key indicia is legible.

A non-transitory computer-readable medium having instructions imbedded thereon for providing media with a data network, wherein the instructions, when executed by one or more computers, cause the one or more computers to:

• obtain a light level sample from the light sensor;
• and
• turn the backlight:
• from off to on when a light level sample is less than a first threshold value below which backlight illumination is used, the first threshold value based on a first contrast ratio between light and dark regions of key indicia, and
• from on to off when the light level sample is greater than the first threshold value but less than a second threshold based on a second contrast ratio between the light and dark regions of key indicia, the second contrast ratio being less than the first contrast ratio, the second contrast ratio based on a minimum contrast at which the key indicia is legible.