Light
Plant growth involves the conversion of light energy into plant-building materials (photosynthesis, see chapter 2). Two factors are important for optimal growth. In the first place, the light intensity. Light intensity is expressed in ‘lumens’. At least 50,000 lumens are needed for growing indoors. It’s not sufficient to add up the number of lumens listed by the manufacturer for each lamp. The total number of lumens given off is depends strongly upon good reflection, and proper connecting fixtures and starter ballasts for the lamps. The quality of the reflector used, and the connecting fixtures and ballasts determine the light yield for the greatest extent. For those reasons, self-built sets and home-designed illumination often deliver a lot less light yield than lamps being used in professional horticulture. We can improve the light yield in our grow room by applying reflective material. We haven’t painted the walls of the room matt white, and used reflector caps for the lamps for nothing! The second important factor is the wavelength of the light. For the production of chlorophyll, and an optimum photosynthetic reaction, light from the blue spectrum (445 nanometers), and light from the red spectrum (650 nanometers) is necessary. Blue light ensures optimal phototropism. Phototropism is the phenomenon which causes plants to grow towards the light, and to spread their leaves in such a way to receive the most light.