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The Hydroponics Manual: Lighting

250W / 400W / 600W quality light with ballast featuring combined timer. The timer is shown as the dial on the top of the ballast. 600W water cooled high pressure sodium light and reflector.

With the correct lighting, you can grow almost any plant indoors. The most important thing to know is the level of light that a particular plant needs for successful growth. For example, houseplants and ferns do not need as much light as salad greens and culinary herbs. Tomatoes, orchids and flowering plants require the highest intensity light of all. The most common mistake made by indoors growers is to provide inadequate light, usually because they try to cover too large an area with the light available. It is important to remember that a smaller area with adequate light will give better results than a larger one without.

Fluorescent Lighting

Fluorescents are highly suitable for small scale salad and herb gardens indoors and are also ideal for the production of seedlings and cuttings. While it is certainly possible to grow larger plants under fluorescents, it is not really practical as they would need to be closely packed together and kept constantly close to the light.

High Intensity Discharge Lighting

To grow vegetables, flowers and other light loving plants, the home gardener need look no further than the modern HID light which is simple to use and which will cover a large area in which the grower can place almost any type of plant. HID lighting has come a long way in the last few years. New developments in lamp and reflector design have improved their efficiency beyond anything imaginable a few years ago. Instead of being a specialised piece of kit for the commercial grower, they are now just another appliance that you simply hang up and plug in. We have no hesitation in saying that this is the single most valuable purchase for the keen hobby gardener because it will extend gardening pleasure into 12 months and allow for the cultivation of many unusual and delicate plants that are otherwise unsuitable for this climate.

HID lights are available either with remote ballasts, or as fully integrated units. Some growers still prefer the remote fitting because the ballast can be placed on a shelf and only the lightweight reflector unit needs to be suspended from the ceiling.

There are basically two types of HID lighting available to the hobby grower. Metal Halide, with its blue white light, was long recognised as the best all round light for plant growth while the High Pressure Sodium with its red / orange light was understood to be the best for the flowering and fruiting cycle of plant growth when light of this colour is more readily used. Many growers still follow this pattern, either by using Halides for the first part of their growing cycle and switching to Sodiums during the flowering cycle, or by mixing the two together throughout the crop.

Modern research, however, has indicated that the latest Sodium lamps which have enhanced levels of blue white light, are more than adequate light sources for every stage of plant growth. These lamps are known as "Agro" or "PLANTA" and they are used by many growers for their entire growing season covering many different types of plant. Sodium lights are the first choice of professionals and most of the recent research are in this area. Sodiums are much more powerful and efficient than Halides and they are improving all the time.

HID lights come in various wattages from 250 up to 1000 and beyond. All these lights can be used with good results provided they are well located in the growing area. Most common wattages are 400 and 600 but some growers prefer the 1000 watt units for their sheer power. The most efficient wattage for indoor growing is the 600 watt sodium lamp which produces an astonishing 92000 lumens (light output).

There are many manufacturers of horticultural lighting and most of them have concentrated on cheap products to service the lower end of the market. This is a shame as lighting is one area where it does not pay to use the cheapest available. Some of the lights on the market are very crudely made and care should be taken to check that lights are manufactured to EEC standards.

The best products are based on years of research and computer assisted design and on access to the very latest in lamp technology. The result of all this investment is seen most easily in the best reflector designs which are fine tuned by years of experience to reflect the absolute maximum level of light onto the plant area. If you compare well designed reflectors such as SuperNova with the basic folded metal designs put out by other manufacturers, it will be easy to see why they will give you superior results. It must be remembered that any 400 watt light will take the same amount of energy (money) to run but a well designed reflector will increase the light available to the plant by up to 30%. This extra light will not add to your running costs, it is free!

Lamp Recommendations

400W high pressure sodium Son-T Plus light bulb, 400W high pressure sodium AGrow bulb and 400W metal halide bulb.

Use Lamp Recommended
Single lamp for general gardening Metal Halide
Two lamps for general gardening 1 Metal Halide, 1 Hight Pressure Sodium
More than two lamps for general gardening 1 Metal Halide to every 3 HP Sodium
Specific attention to vegetative growth Metal Halide
Specific attention to flowering / fruiting HP Sodium

More Light for Less Money

All 400 watt lights will use 400 watts of electricity; they will cost the same to run. This is why it is so important to maximise the light that your plants receive from your electricity input (money). The first step is to ensure that you have a well designed reflector. The cheap ones on the market are cheap for a reason and can be up to 30% less efficient than a top end model. SuperNova reflectors are based on computer designs and light meter testing over many years of modification and improvement. They are based on a double parabola that deflects light and heat away from the lamp itself. This design maximises light reflection onto the plants and also improves lamp life. The extra light that a SuperNova can deliver to your plants will cost you nothing. A few more pounds on the reflector maybe, but the extra light efficiency will be free thereafter. SuperNova reflectors are available from Esoteric Hydroponics.

1. Light Movers

A lamp moving overhead will increase the intense light that the majority of plants receive. This is a more efficient way to use an HID lamp and should be considered by every grower. Fortunately technology has come to the growers’ rescue yet again in the form of the amazing Light Rail 3. This simple but highly effective device is based on a six foot rail or track with a precision engineered carrier that quietly moves your light back and forth over the growing area. The sun moves so why shouldn’t your light?

Light Rail 3 allows you to cover a greater area with no significant electricity use and ensures that all plants receive the same level of light. This ensures that you will have uniform growth and the plants in the corner will grow as well as those in the centre. It saves you having to move your plants around under the light source. In addition, Light Rail 3 eliminates shading so there will be much more even growth from the top to bottom of the plant. Another advantage of light movers is that you can get your lights much closer to the plants without burning the foliage. It is a great way to get better results from your lights without spending more on electricity. Light Rail 3 uses 5 watts of electricity and costs abut £2 a year to run. It is a world wide product that has been extensively tested and developed under actual growing conditions. Using Light Rail 3 will ensure that you can adapt your growing area to changing circumstances or move easily into a new area. Basically, a linear mover such as Light Rail 3 will be best suited to square or rectangular growing areas while the rotating movers will work best in circular rooms. It is a superbly simple piece of kit and the unconditional guarantee reflects the manufacturer’s confidence in it.

There are also Light Movers on the market that move the lights in a circular pattern. These may prove very useful. The Sun Circle Light Rotator allow the grower to use combination lighting, ie Metal Halide on one arm, and a High Pressure Sodium on the other. This produces a perfect balance of spectrum of light for growing and flowering, thereby maximising efficiency and promoting all round growth and stronger plants.

Just contact Esoteric Hydroponics for further information.

SunCircle light mover with two arms.

2. Reflected Light

Proper attention to reflectivity can increase the amount of available light by up to 30%. It is important that the plants are surrounded as closely as possible by reflective surfaces. This can easily be achieved by placing the lamp in a corner of the room and constructing two lightweight, mobile walls of reflective material which can be moved out as the plants grow bigger. Walls can easily be painted with flat white paint which is an excellent reflector. If it is not possible to paint the walls, they can be hung with Black / White plastic film which can also be used for the floor. Polystyrene foam sheeting can also be used in many different ways. It is superbly reflective material and highly recommended. The ultimate reflective floor covering is brilliant white vinyl which is tough and hard wearing. The most reflective material of all is the space age material MYLAR which is like a flexible mirror and can reflect 92% of light back onto the plants. MYLAR is available from your local dealer.

The following table will illustrate the reflective value of the various materials available to the home gardener:

Reflective Chart
Material Reflectivity
Black Less than 10%
Aluminium Foil 55-70%
Semi-gloss White Paint 60-70%
White / Black / White Film 70-85%
Flat White Paint 75-80%
Polystyrene Foam Sheeting 75-85%
Mylar Sheeting 90-92%

Contrary to popular belief, aluminium foil does not provide a good reflective surface even when it is flat. As soon as it becomes creased and crinkled, which it inevitably does, it will become even less effective.

A far better reflective surface can be achieved with a couple of coats of flat white paint, windows and fireplaces can be covered with Black / White or White / Black / White plastic film which also makes an excellent reflective floor covering.

Be careful when you choose your paint. The one to use is the water based flat white that contains no varnish substances which are known to absorb certain colours in the spectral waveband. Glossy paint should not be used as it lends itself to bright spots and glare. In a temporary situation where you may not wish to use paint, we would strongly recommend polystyrene foam sheeting. These sheets can be attached to the wall with blue tack and removed at the end of the crop.

Polystyrene is a brilliantly reflective material. It is always good to have a few spare sheets on hand as it can be used in many different ways to maximise the light around your plants.

White / Black / White plastic film is another excellent material that has helped to make indoor gardening possible. As its name implies, this tough film is white on each side with a black layer sandwiched in between, so it can perform an important dual function of excluding unwanted light on the one hand and reflecting desirable light on the other. Provided that it is carefully placed, this film can be used to make a room completely light-tight. In the first place, it can be used to cover windows when constructing your grow room. This is extremely important if you are using grow lights as an uncovered window will tend to light up large areas of the neighbourhood which can attract attention and possibly invite burglary or vandalism. In the second place, the exclusion of all natural light will allow you to have total control over your plants’ light source. Control of the light source means that with certain species, for instance, flowering can be induced by reducing the light hours. This is a commercial technique favoured by flower producers such as chrysanthemum growers. White / Black / White plastic film can also be used as a floor covering which will help protect carpets from water or nutrient solution which can easily be spilt or splashed. White / Black / White is available by the linear metre from any grow shop.

A combination of white paint, polystyrene sheeting and White/Black/White film will allow you to build a growroom in which all the visible surfaces are white. This will ensure the maximum use of light that you are providing. Any dark walls or furniture will effectively act as "holes" through which your light will escape.


The use of an efficient timer is absolutely essential for the indoor or greenhouse grower. Timers are used to automatically turn your lighting system on and off. Indoor plants require between 12 to 18 hours of light a day and it is essential that timers are reliable. A failed timer could mean that lights remain on for 24 hours which will have a big impact on your power bill and could also completely disrupt the flowering cycle of certain plants such as chrysanthemums which require specific light hours to flower successfully.

Ordinary plug-in timers can be bought cheaply enough at your local DIY store but they are not suitable for more than one or two lights and they can be prone to failure. For complete peace of mind, a mechanical timer of industrial quality is recommended. Alternatively, you can use relays or contactors which will divert the power load away from the timer itself. Timers are available from Esoteric Hydroponics.

Power Consumption

The amount of electricity needed to grow plants indoors can be surprisingly small and it should never be seen as a reason not to go ahead. The beginner is strongly advised to work out power consumption before starting, to ensure that the operation will be cost effective. A few figures have been included here as guidance but you will need to check your local rates to see if they apply to you.

Based on the approximate rate of 8p per unit, it will cost 38p per 12 hour day to run a 400 watt light. This would translate to £34 on the average 90 day bill. If off-peak power is available and is used for seven hours out of the twelve, it would reduce that bill to around £25.


Mains Voltage can Kill!

The conditions in a greenhouse or growroom are generally damp and humid. Please take extreme care with all electrical installations. All timers, plugs, sockets and other electrical fittings must be placed well clear of any potential splashes. If you are in any doubt about wiring or any electrical matter, please call a licensed electrician.
Or let Esoteric do it all.

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Manual: Intro | Propagation | Nutrients | Growth Enhancers | Lighting | Hydro Systems | Growing Environment | Further Info | Product Docs

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