One of the most critical challenges—whether for greenhouse managers or for horticulture aficionados—is to provide plants with enough photoperiodic sunlight for effective photosynthesis, so that they can grow optimally regardless of the geographical location and climate. Winter months even in supposedly warm-weather California can have a Daily Light Integral (DLI) of 10 to 20, which is insufficient for optimal plant growth. As a result, supplemental electric lighting is required in most cases to accelerate flower development, create hardier stems, increase chlorophyll content, and also increase leaf count.
Light acts as a key environmental signal and a critical source of energy for plant growth, with plants using light for both photosynthesis and development. Lighting parameters influence germination, seasonal and diurnal time sensing, plant stature, growth habits, and transition to flowering and fruit ripening. It is therefore important to control the quality, quantity, intensity, direction, duration, and wavelength of the light reaching the plants, in order to ensure effective growth, sustained development, and maximized crop productivity.
Light uniformity refers to how evenly the light is distributed across a given growing area, and should be an important consideration—just as light intensity and quantity is—for all types of plant lighting installations. Light uniformity can regulate crop growth, plant development, flowering schedules, and water distribution. If the illumination system for a growing area is not designed to distribute the light in a uniform manner, the crops will dry out or develop at different rates depending on whether they are getting access to more or less light across the same area. If some plants receive more light than others and exhibit uneven growth patterns, that in turn can lead to uneven shading.
Light uniformity is affected by a number of factors, including (but not limited to) the light source used, the reflector design, the type of fixtures, the light distribution, beam angle, fixture quantity, fixture spacing (how close together they are), and the distance of the fixtures from the plants themselves.
A uniform blanket of light can be achieved by equipping the light fixtures with light bars, which can be easily arranged according to desired spacing to achieve effective intra-canopy light penetration. The luminaires with their source type (ideally LED) and light bars should be mounted at an optimum height and spacing—either via calculations or by following manufacturer recommendations—to deliver a uniform layer of light (without creating hazardous light intensity levels or hot spots) over the full plant canopy, even as the canopy grows and changes over time. These techniques will then translate into increased profits per harvest, and will maximize dry growth yields on a continuing basis.
Light uniformity also affects the efficiency of any prescribed nutrients, since plants receiving lower light annually (compared to the targeted average) will consume more nutrients or dry faster due to uneven water use, and that will reduce profits.