Embodiments described herein involve determining an area of interest on a growth media. An overall brightness control value for a plurality of illumination sources configured to illuminate the growth media is calculated. The overall brightness control value generating at least one image that substantially matches a target intensity at the area of interest. An individual brightness value for each illumination source of the plurality of illumination sources is calculated by individually adjusting a brightness of each illumination source to generate at least one image that substantially matches the target intensity in each respective illumination source's area of influence. A calibrated brightness value for each illumination source is determined based on an image intensity with each illumination source turned on at the respective individual brightness value and an intensity that each illumination source generates within each respective area of influence when turned on alone.