The quality of a grow light can be understood by looking at the spectrum of that light source. Natural sunlight is intense and has a broad, balanced spectrum. Indoor plants require the same high intensity and broad yet balanced spectrum.
So what is a spectrum? A light spectrum is the many different wavelengths of energy particles, called photons, produced by a light source. Those photons are measured at specific nanometers (nm) representing a wavelength of light or band of light energy. Visible light is the part of the spectrum from 380nm to 780nm. Plants utilize spectral energy from 300nm to 800nm.