Illumination system

An illumination system arranged to illuminate a space for rearing a flock of birds, the space being an indoor space of an agricultural facility, wherein the illumination system comprises:

• a visible light source configured to emit visible light;
• an ultraviolet light source configured to emit ultraviolet light;
• a controller configured to:
• (i) set a circadian cycle to entrain a circadian rhythm of the flock of birds by controlling the visible light source to emit the visible light for a predetermined period of light, and not to emit the visible light for a predetermined period of dark;
• and
• (ii) control the ultraviolet light source to emit the ultraviolet light at an ultraviolet light intensity for at least one subperiod within the predetermined period of dark, wherein the ultraviolet light comprises a peak wavelength within the UV-A wavelength range;
• wherein the illumination system comprises a sensor unit configured to detect, during the predetermined period of dark, a property indicative of at least one bird of the flock of birds being awake;
• wherein the controller is configured to control the ultraviolet light source to emit the ultraviolet light at the ultraviolet light intensity for a subperiod within the predetermined period of dark when said property is detected.