Day length; the relationship between the length of light and dark in a 24 hour period.Synonyms: ScotoperiodRelated Articles: How to Measure Horticultural Lighting Performance - Part OneHow Light Impacts Plant Development: Photomorphogenesis - Part 1Determining the Ideal LED Grow Light SetupLighting and Lighting Controls in a Greenhouse - Part 1Lighting and Lighting Controls in a Greenhouse - Part 2