Re: Growing Food in Space
It's possible that for the initial stages of the experiment, they want to limit the variables. A controlled source of light at specific wavelengths would help this.
It should also be noted that a long-range spaceship of the sort that requires an onboard ecosystem would probably be nuclear powered, in which case the energy and heat-dump requirements of artificial lighting would be lost in the noise compared to the energy available and the radiator requirements of a nuclear system.