Review of Targeted Lighting Approaches for Controlled Environment Agriculture in Space Habitats

Providing light to plants is expected to dominate the operational costs of agriculture in space habitats. Not only is lighting power intensive, but power introduced into a crop chamber must also be removed to maintain thermal equilibrium. To decrease the power and subsequent cooling demands, advancements in lighting methods must be implemented. Lighting efficiency improvements are limited as LEDs are converging to their maximum theoretical efficacies, which also reduces the effect of optimizing the spectrum to boost efficiencies. Instead, one could consider the effectiveness of light delivery to the canopy by each diode. Plant chambers like the Veggie and the Advanced Plant Habitat on the International Space Station provide power uniformly across the light fixture, often lighting walls and empty spaces, especially when the plants are small. To help ensure that light introduced to the growth area is useful, light fixtures may employ a targeted approach, where emitters are controlled such that those pointed directly towards foliage are activated while others are not. This paper reviews previous targeted lighting approaches and identifies a candidate method that could be applied in future controlled environments, especially those aboard space habitats.