A brightness compensation device includes a panel, a heat detector, a memory, and a processor. he processor is configured to perform the following steps: at a specific grayscale of the red grayscale data, the green grayscale data, or the blue grayscale data, adjusting a turn-on time data of a luminous signal according to the first temperature data; adjusting the red grayscale data, the green grayscale data, or the blue grayscale data according to a brightness relation or the sheet to obtain a red updating grayscale data, a green updating grayscale data, or a blue updating grayscale data; and when it is determined that the second temperature data is the same as the first temperature data, outputting or storing the red updating grayscale data, the green updating grayscale data, or the blue updating grayscale data.