The application of LED (Light Emitting Diode) has been expended from indicating to lighting along with its improvement of brightness. Desk-top lamp is a common lighting device which is used to supplement the darker area. This paper proposed an algorithm to adjust the output brightness in keeping it at the working area at the setting value. Furthermore, the proposed accumulated slope algorithm would reduce the required time in determining the adjustment of brightness as well as if the cause of brightness variation is only due to turning pages or writing.