The screen will be dimmer when running on batteries alone, but bright when you hit the button on top, unless you have the USB cable connected in which case the screen will be really bright. Features & Specifications: – 12 or 24 hour format – LCD screen – Alarm and snooze function – Temperature display 0-37C – Night screen brightness setting – USB power cable included – Material: Acrylic case, Black LCD screen – Colour: Black – Movement: Digital – Power: Connect to DC or 3 x AAA (not included) – Dimensions: LWH 10.5 x 11.5 x 11cm – Weight: 0.20kg