Visible light represents a promising innovation for developing an activated sludge (AS) system. About 95% of AS microorganisms are bacteria, and their responses vary based on bacteria type, wavelength, intensity, and exposure time. An experimental apparatus was designed and constructed to identify the most effective wavelengths of visible light on Pseudomonas stutzeri and Leuconostoc mesenteroides ssp. cremoris. Three wavelengths (white, red, and blue light) were provided at fixed intensity. Optical density was used as an indicator to evaluate bacteria performance. The experimental results show stimulation for P. stutzeri reached (67.45, 62.47, and 38.1%), respectively under white, red, and blue relative to control at (1440 minutes). On the other hand, L. cremoris stimulated under a red light only reached (22.11%), while it’s inhibition under white and blue light reached (34.32 and 27.19%) relative to control. Maximum growth rate (μ) for both species of bacteria achieved under red light reached (0.004122 and 0.004214 min-1), respectively compared to control (0.001579 and 0.002282 min-1) at (960, and 720 minutes), while, maximum inhibition achieved under blue light was (0.002231 and 0.001362 min-1) relative to control (0.001579 and 0.002282 min-1) at (≤480 minutes), respectively.