Dark cavity lighting system

A dark cavity lighting system, comprising:

• at least one horticultural lighting fixture configured to emit a spectrum including
• a first spectral feature in the form of a spectral peak having its peak wavelength in the blue wavelength range of 425-475 nm,
• a second spectral feature in the form of a spectral valley having its base value in the cyan wavelength range of 475-500 nm,
• a third spectral feature in the form of a broad-band spectral feature extending throughout the green wavelength range of 500-600 nm,
• a fourth spectral feature in the form of a spectral peak having its peak wavelength in the red wavelength range of 625-675 nm, and
• a fifth spectral feature in the far-red wavelength range of 700-800 nm,
• wherein
• the fourth spectral feature has a maximum relative emission intensity that is the highest relative emission intensity within the spectrum,
• the first spectral feature has a highest relative emission intensity that is non-zero but less than the maximum relative emission intensity,
• the third spectral feature has a highest relative emission intensity that is non-zero but less than the maximum relative emission intensity,
• the base value of second spectral feature is below all relative intensities of the third spectral feature, and
• the fifth spectral feature has a non-zero relative intensity that is below the maximum relative intensity.