This depends greatly on the specific situation. 940nm is considered “fully covert” as the illuminator’s output is nearly invisible to the human eye. 850nm is considered “semi-covert” and has an output that produces a soft red glow at the illuminator’s front cover. The light produced by our white light illuminators is fully visible and has a color temperature of 6500K (cool white). The benefit of using the 850 or 940nm wavelengths is that they do not produce “light pollution”, which is desirable in some circumstances and dictated by law in others. The benefit of white light is that well lit areas are a proven strong deterrent against crime. In order to use the 940nm or 850nm models, the security cameras being used must be “true day/night” cameras. These cameras are equipped with an IR cut filter that is mechanically removed in low light conditions. Cameras with a non-movable IR cut filter will block the light produced by the 940 and 850nm models. When choosing between a 940nm and 850nm wavelength, it is important to know that most cameras are less sensitive to the 940nm wavelength. This is why the illumination distance specifications are shorter for these models. For this reason, 940nm is typically used only when the illuminator must be “fully covert”.