A load effect compensation system, display device having the same, and method of compensating load effect of display panel are disclosed. In one aspect, the load effect compensation system for a display device includes a light sensor operatively connected to a display panel and configured to detect an amount of light emitted from the display panel and a light converter configured to convert the detected amount of light into a load amount. The system also includes a data corrector configured to receive the load amount and an image signal and adjust grayscale values of the image signal based at least in part on the load amount.