Lighting the Hydroponic Garden

Most plants that are grown in a hydroponic setting require light, lots of it. This is because they photosynthesize to produce their own nutrients. They require warmth, not only to keep biochemical reactions going but to keep it going at the right rate. A hydroponic setting regulates many processes by the amount of light present, speeding some up and shutting down others.

During photosynthesis plants take in carbon dioxide and water to produce glucose and oxygen. The glucose is used as an internal energy source and much of the oxygen is expelled; but the color and intensity of the light they receive plays a large role in how plants do that.

The fact that leaves are generally green and/or yellow shows that those colors are being reflected. The other components of white light (which is a mixture of many wavelengths) are mostly absorbed by plants – but some are taken in more efficiently than others at different growth stages. The wavelengths that we perceive as red in the spectrum range are used more during growth phases. Blue on the other hand is absorbed more to produce flowering or fruiting.

Since few hydroponic gardens are simply left out in the sun to take their chances, a lighting scheme is required to assist them in all those activities. Plants that sit near an open window or which are grown outdoors largely self-regulate the wavelengths they absorb, where the whole spectrum is abundant. On the other hand plants that live indoors can only take up what is available – this makes it important to ensure that they have all they need, both in terms of intensity and wavelength.

Indoor lights are typically less intense than natural light as they provide less overall energy and therefore plants may need to be supplemented with natural light. In some cases it may be necessary to use special lights to provide the total amount of light energy needed for warmth, photosynthesis and other useful tasks. However, the mixture will vary from one climate to another.

Indoor lights come in a variety of types, prices and wavelengths, some are better than others for plants. Incandescent lights for example provide a lot of heat – and this is the reason that they are relatively inefficient in electricity usage. However, incandescents at the red end of the spectrum produce strongly while they produce a lot less in the blue range.

In contrast to incandescent lights many fluorescents tend to produce greenish light. This is because they are filled with mercury and the interior coatings that produce light in the visible range may be better or worse at producing a white-approximating spectrum. However, in the long run these are much cheaper to use.

A relatively inexpensive setup can be achieved with a mixture of incandescent and fluorescent lights. A 30-watt incandescent with a 100-watt equivalent fluorescent provides a good balance of wavelengths – fluorescents use much less electricity so the wattages can’t be directly compared.

Metal halide and sodium lamps make for very good lights for hydroponic gardens even though they are more expensive. Metal halide lamps produce well in the blue range and sodium lamps provide more reddish light. The bulbs can’t be switched between fixtures so it is necessary to buy a housing fixture that is appropriate to each type.

Some newer LED lamps will produce a very broad spectrum and some can be adjusted to favor one wavelength range. However, they are expensive and many will not produce the same output as other types. In addition to this plants vary in the intensity of light they require; you should try to ensure that medium light plants receive at least 1,000 foot-candles while others will need 2,000 foot-candles (about 20 watts per square foot) or more. A good light meter will tell you how much is being given off, or you can sometimes find the rating listed on packaging or advertisements.

Plants that receive sunshine will need from 8-10 hours per day. If only artificial lighting is used, the number rises to between 12-14 hours per day. For some plants and lighting schemes 16-18 hours per day may be needed as the specific number depends heavily on the type of plant.