Hydroponic Lighting

Artificial Light

Usually, natural sunlight is used for this important job. However, during the shorter and darker days of winter, many growers use artificial lights to increase the intensity of light (for photosynthesis) or to expand the daylight length. While the sun radiates the full spectrum (wavelength or color of light) suitable for plant life, different types of artificial lighting are selected for specific plant varieties and optimum plant growth characteristics. Different groups of plants respond in physically different ways to various wavelengths of radiation. Light plays an extremely important role in the production of plant material.

The lack of light is the main inhibiting factor in plant growth. If you reduce the light by 10 percent, you also reduce crop performance by 10 percent.

Light transmission should be your major consideration when purchasing a growing structure for a protected crop. Glass is still the preferred material for covering greenhouses because, unlike plastic films and sheeting, its light transmission ability is indefinitely maintained.

No gardener can achieve good results without adequate light. If you intend to grow indoors, avail yourself of some of the reading material that has been published on this subject. If you are having trouble growing good plants, then light is the first factor to question.

Natural Light

A large part of the success in growing hydroponically is planning where to place the plants. Grow plants that have similar growing requirements in the same system. Placing your system 1-2 feet away from a sunny window will give the best results for most herbs and vegetables. Even your regular house lights help the plants to grow. Make sure that all of the lights are out in your growing area during the night. Plants need to rest a minimum of 4 hours every night. If your plants start to get leggy (too tall and not very full), move the system to a spot that has more sun. Once you find a good growing area, stick to it. Plants get used to their home location. It may take some time to get used to a new place.

Lighting Terms and Definitions

Ballast
The electrical components (usually a transformer and capacitor) that energize a high intensity bulb.

Color Temperature
(also known as Kelvin temperature or correlated color temperature)  A measure of color of light emitted by a bulb in comparison to black.  This is used as a general meaure of a bulb's coolness (whiter light) or warmness (redder light).

Footcandle
A unit of illumination equal to the intensity of one candle at a distance of one foot.  Footcandles are usually used as a measure of light received.

Lumen
A unit of illumination; a measurement of light output.  One lumen is equal to the light emitted by one candle that falls on one square foot of surface located one foot away from the candle.

Photoperiod
The relative hours of light and darkness in a 24-hour period.  Some plants respond to a change in day length (photoperiod) in order to grow or flower.

Photosynthesis
The process by which plants use light energy to collect carbon dioxide from the atmosphere and convert it to chemical (growth) energy in the form of carbohydrates.

Metal Halide lamps and High Pressure Sodium lamps belong to the
H.I.D. (High Intensity Discharge) family of lights.
Metal Halide and High Pressure Sodium lamps are used for garden lighting because of their high light output per watt, and the spectral distribution of their light.

Metal Halide / Daylight / MS Lamps - These lamps emphasize the blue / green spectrum to promote vegetative growth. If you have little or no sunlight available these are the systems to use. MS lamps contain a 30% boost over standard Metal Halide lamps in the red/orange spectrum and more lumens per watt than standard Metal Halide lamps.

High-Pressure Sodium - These lamps are primarily red/yellow in spectrum. These are the best lamps available for use in conjunction with natural sunlight. High-Pressure Sodium lamps promote budding and flowering in plants.

Conversion Bulbs - There are two types:

1) Sodium bulbs which run on Halide ballasts.

2) Halide bulbs which run on Sodium ballasts.

A conversion bulb lets you tailor the light source to the growth stage of the plant merely by changing lamps.

Flourescent Lamps - These lights are perfect for starts and seedlings. They are generally a poor light source for production growth and flowering because of their low lumen output, although they may be used in some instances for small scale systems with low growing plants, ie: lettuce, basils, etc. Plant growth will not be as rapid as under HID lighting due to lower light levels.