Most plants require light exposure, to facilitate photosynthesis. Different organisms, or organisms at different points in the growth process, may require higher or lower levels of light intensity:
- Seed germination – very low light levels, typically under 80 micromoles
- Plant tissue culture – low light levels, 50 – 150 micromoles
- Arabidopsis and Algae – medium light levels, around 300 micromoles
- General crops and ornamentals – high light levels, 400 – 500 micromoles
- Cannabis and tobacco plants – very high light levels, in excess of 900 micromoles
- Plant pathology studies - medium to low light levels, 150-300 micromoles, with special coated refrigeration system if flying insects are involved.
Plant growth light sources are all designed to produce the maximum proportion of Photosynthetic Active Region (PAR) wavelengths to total luminous output. Plants can only utilize light in the 400 – 700 nanometer range for photosynthetic activity. Within that range, the chlorophyll that drives biomass production is most active within the 400-480nm and 620-680nm regions. Being able to control the ratio of “red” to “blue” light, as well as having small quantities of “yellow” and “far red” light, can also provide valuable research insights into plant flowering, height, and accessory pigment production.
Within an artificial growth environment, light must be controllable, creating light/dark states similar to natural diurnal cycles. In reach-in plant growth chambers, this is accomplished through a combination of light-tight doors, uniform chamber lighting, and controls that can be programmed to turn the lights on and adjust their intensity on a time-based schedule. Light control features, such as gradually turning them on and off to simulate sunrise and sunset, also help to build a realistic growth environment.
Light adjustability is not only featured to produce the exact illuminance required by the organism being grown, a but also to deliver a given illumination level at the level of the plant where most photosynthesis takes place. Measured illuminance drops off progressively as you move away from the light source. Using a combination of shelf-specific light banks, adjustable shelves, dimming light sources, and an integrated photo meter, chambers can be “tuned” to provide specific light intensities where plants need them most.
Plants require uniform temperature, to prevent leaf damage and general desiccation. This is especially challenging in a growth chamber, where heat from light sources can easily create localized hot-spots. Selection of an efficient light source, as well as plenum-directed airflow, can reduce heat near the plants, and distribute generated heat evenly within the chamber.
Finally, plants also require moisture, though in reach-in chambers, this is often provided by periodic manual watering or an external watering system. Controlled or elevated RH systems integral to the cabinet can also be used to increase or decrease humidity, to match specific growth conditions.