Light burn is the bleaching of leaves and flowers caused by excessive illumination. In other words, your lights are too close to the plants!
Too much light is stressful to a plant, even if the canopy temperatures can be kept cool. Light intensity can be measured with a PAR meter or a less expensive LUX meter. A good canopy PAR reading in veg is 600-800 micromoles. A good canopy PAR reading during flower is 800-1100 micromoles. If you’re using a LUX meter, use the chart below to dial in proper distance based on the light source you are using.