Light

Light is the energy that creates life. Life cannot exist without it, and cannot thrive without enough of it. Plants process up to 5,000 foot-candles of light intensity to get the energy to grow. The sun is around 1,000,000 foot-candles.  Shade can be lower than 1,000 foot-candles.

Plants will enjoy much light, but some do not like all the heat put out by sunlight. Shade cloth is ideal for hot conditions, also to keep plants from, insects, wind, rain and other damage, but rarely is the requirement for low light levels.

Sunlight is an ideal source of light for plants. It is bright and contains the Reds and Blues necessary to produce good healthy growth. However it also has infrared, Green and Ultra-Violet light.

The infrared light or heat is absolutely necessary or we would all freeze to death, but it can be too little or too much heat. Too little heat is best combated by using a recirculating hydroponic system. By heating the nutrient in the tank, and pumping the 20 to 25C nutrient around we can keep the plants warm.  Excess heat in summer, can be alleviated by cooling the tank, usually by aerating the tank heavily. By using a venturi, a water jet, or having the nutrient rising and falling into the tank like a waterfall will cool the nutrient as it passes through the air.
It is not necessary to worry about green light as it is usually reflected off the leaves, making them look green. There is some evidence that shows that a reduction in Ultra Violet (or UV) light can improve growth. If you are growing under glass or plastic this may interest you.

We generally grow outdoors, so just use common sense. If you’d feel hot or cold in the sunlight, then the plants would feel that too. Plants tend to grow well in the same climate as humans feel comfortable.  A great way to grow is under artificial horticultural lights that will allow more control, and less damage from the elements, but that is a decision you can make. What I can tell you is that, a 400-Watt plant light, costs very little to run, but the benefits are, faster growth (from up to 18 hours of light per day), more control of the seasons through day length, less pest problems, no wind, rain and less cold problems. But you may need an exhaust fan to ensure good air circulation and no heat build up in warm climates.

RULE: A PLANT GETS ALL ITS ENERGY FROM THE LIGHT IT ABSORBS THROUGH ITS LEAVES. LOWER THE LIGHT LEVELS AND YOU REDUCE THE GROWTH RATE.

The grow light reflector or hood is used to direct the light towards your growing area. There are literally hundreds of different designs and makes on the market; however, they all do more or less the same thing. The hood usually has a reflective insert to provide greater light intensity and/or to reduce the amount of light that is double reflected in one area, normally directly under the bulb. (This intense light area, known as the sweet spot, can cause a reduction in plant production and growth, giving rise to uneven cropping). You can either purchase a complete system that includes everything you need to get started, or select your ballast, reflector and bulb, separately.

High Pressure Sodium’s are available in 400 Watt and 1000 Watt sizes, as well as other sizes. They emit a spectrum of red/orange/yellow and have been compared to the autumn or harvest sun. There has been in the past, considerable debate over whether Halides or Sodium’s are more suitable for plant growth. The High Pressure Sodium lights are best known for their longer life, higher light output and flowering capabilities, but with less blue light than Halides, some plants may not produce the healthy vegetative growth when used alone. High Pressure Sodium are ideally used in conjunction with Metal Halides to produce a brilliant plant growth environment, and an excellent spectrum full of high energy reds, and blues that keep the plant compact and healthy. Sometimes Halides are used up to the flowering stage and High Pressure Sodium is used from this point for increasing the flower/fruit size and weight. Son T Agro Lamps (see below) are an example of a lamp designed to incorporate these two spectrums. High Pressure Sodium’s require High Pressure Sodium Control Gear.
Because of the requirement for different Halide and high-pressure Sodium control gear (also known as ballast) the retrofit bulb was created.

MH - Metal Hailide

Metal Halides are available in 400 Watt (60,000 foot-candles) and 1000 Watt (100,000 foot-candles), and sometimes in other sizes. They emit a blue/white light and are used for increasing plant growth rates, controlling the seasons (Photoperiodic control) and for indoor growth, away from pests, disease, wind, rain, heat or cold extremes, as well as the healthy growth characterised by these plants. Hobbyists use these lights for these reasons and for limited growing areas where indoor gardens may be either more viable or decorative. Metal Halides are very suitable for healthy vegetative growth, flower growth and produce excellent large, bushy plants. These lamps require Metal Halide control equipment, which is sort of like a transformer and starter put together.

Flouresent - T5's, T8's

The common fluorescent tube relies on fluorescence. Inside the glass tube is a partial vacuum and a small amount of mercury. An electric discharge in the tube causes the mercury atoms to emit light. T-5's are best used for vegative growth. Low heat allows you to get the light close to the canopy of the plant. Low power consumption is also a added bonus. Fluorescent tubes have been used for seedlings, tissue culture and cuttings for a great number of years. The most commonly used is GROLUX and Activa 172 tubes, but also Powertwists and other speciality Fluroscents, as well as Cool White tubes (as used in plant terrariums e.g. Phototron). By using Fluorescent tubes, to achieve mature growth, plants must be grown as close to the tube as possible, without touching the tube, as this may cause burning of plant tissues.
The closeness of the tubes is required as each tube only outputs the minimum light required for plant growth (about 1000 foot-candles) and if further away from the tube, the output of the light diminishes. Always use a horticultural reflector. Because a fluorescent tube is round, light is travelling in all directions from the tube, and any light travelling upward, or sideways will miss the plants below. Reflectors redirect this light in a favourable manner and generally increase the light to the plants by 50% to 95% with any standard lamp.
The benefits of Fluorescents are smaller internodal lengths, smaller leaves and smaller flowers but more numerous. Plant growth may be slower than expected.

Photoperiods for Vegative Growth and for Flowering

For flowering plants 12 hours on and 12 hours off. For vegative growth 18 hours on and 6 hours off.