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Don’t waste a Watt – a look at a range of reflector designs |
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| A look at some of the reflector types available for high pressure sodium and metal halide systems and some of the differences which make different reflectors appealing to different people and certain applications. |
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Introduction to Light - Propagation of light energy waves
Light, whether from the sun or from an indoor grow light is basically electro-magnetic radiation. Carrier waves bring light to us in a frequency range we can see, with changes in wavelength of the received light appearing as different colours.
There are other forms of electromagnetic radiation that we don’t see because the frequency and wavelength of the carrier wave is out of our visual sensitivity range. These include cosmic rays and gamma rays (nuclear radiation) which are too high a frequency and too short a wavelength too see. At the opposite end of the scale with lower frequencies and longer wavelengths are radio waves and electric waves, which are too low too see but are useful for transmitting information on.
Light, like all wave energy travelling through any atmosphere, gas, or liquid, it is subject to four main physical effects:
1. Attenuation - power extracted from the signal. This happens in two main ways:
a) As the light passes through the air (or other gases or liquids) the amount of light is depleted. You can see this with water as daylight in the sea only penetrates the first few metres due to the absorbtion and scattering of the light. In space there is no attenuation of the light and we can see stars millions of miles away. In gases like air the loss of light over a distance is quite high and this is why it is important to lose as little as possible on reflective surfaces. Light in your growroom is subject to the Inverse Square Law. This law applies to the movement of light energy through the atmosphere and it says, ‘the light energy available is in inversely proportion to the distance it has travelled’. Or, put another way if an object is twice the distance from a light source, it would receive a quarter of the light and if an object were four times the distance it would receive a sixteenth of the light.
b) As the light hits and passes over surfaces like walls, reflective sheeting, water, and most of importantly of all the reflector, some light is absorbed and scattered or attenuated as electrical charges are induced in the surface and power is extracted from the light signal. As well as a reflector needing good spread and uniformity of intensity this also needs to be balanced with avoiding heat build up and minimizing attenuation of light by using the right amount of the right materials.
2. Refraction - Refraction happens when the light energy is bent from it’s straight line path through the air due to changes in humidity and temperature through the air, this doesn’t effect us too much growing indoors with lights.
3. Diffraction - The ability of light energy and all kinds of wave energy to bend around objects in it’s path. This is purely dependent on the wavelength and frequency of the energy wave or in this case light. As wavelength is increased (frequency decreased), diffraction increases and scattering effect is also reduced.
4. Reflection - This is the ability of light to be reflected. During reflection how much of the light wave radiation will be reflected and how much will be attenuated will logically depend on the size of the surface, what the surface is made from or covered with, the distance of the reflective surface from the from the light source and the angle at which the light hits the surface. In regard to reflectors not only does the light need to be reflected down with as little loss(attenuation) as possible, but the light also needs to be reflected in a way to give good spread, and uniformity of intensity over that spread, this is about good design and size as well as choice of materials.
These things effecting the propagation of light energy have an effect not only on ‘lamp from plant distances’ but also in relation to reflector design and materials used and reflective surfaces in general in the grow room.
Reflectors
The main attributes that a reflector needs to have are the ability to provide good spread, good intensity and good uniformity of intensity over the required area without incurring heat problems.
The main types of reflectors:
Open Ended Reflectors
These are the most popular type of reflector. The Adjusta-Shade and the Silver Wing are classic examples. Open ended reflectors let a lot of the heat associated with the lamp escape and consequently can be placed closer to the plants than closed ended reflectors. When growing in high light growing environments, especially with more than one light, they do give the heat an escape root rather than being directed down toward the plants. In practice these type of reflectors are very effective in any situation.
Closed End Reflectors
Close ended reflectors often have a better uniformity of spread and a better block of light than open reflectors, but will need to be a bit higher than an open system to avoid heat problems. These types of reflector are often preferred on light rails where heat build up is less of a problem.
Vented Reflectors
Some of the newer close ended reflectors on the market now are well designed and well vented making them perform well whether stationary or moving. One such reflector is the Rising Sun SuperNova. Vented reflectors are very effective in any situation.
Jet-Stream Air Cooled Reflectors
These are the best air cooled shades on the market. Ideally suited to a 600 Watt lamp, the Jet Stream Air Cooled Reflector has 125mm (5”) spigot attachment on each end of the reflector which attaches to an extractor fan and ducting to blow through the shade. Some light is lost through the heat resistant glass cover which encloses the lamp, but most of the heat is removed and the lamp can be lowered down closer to the plants. The fan used to cool the Jet Stream should be separate to the extractor fan used on the grow room itself. These systems are excellent for making the most of small areas where it might normally get to hot with big lights, or when there is limited headroom or multiple lights.
Water Cooled Light Systems
At GroWell we are constantly reviewing and testing a range of potential new products before be decide to sell them, we only want to sell good equipment that is tried and tested and our customer won’t have a problem with. We have had samples of different water cooled light systems but we still haven’t found anything that we’d have confidence in selling. There are two main issues:
i) There is the inherent problem of light loss through water and glass (or similar).
ii) With water and electricity in close proximity, build quality, design and safety become much more important issues than normal. There really is no room for error.
Poot Light Reflectors
The Poot Light ‘Wide’ reflector is supplied as standard with the Dutch Poot System available at GroWell. It has been used for many years in high light indoor applications with outstanding results. It really does perform well as a reflector, with no heat problems and perfect spread of light.
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GroWell Hydroponics Ltd, Solihull, Birmingham, UK
Blooms Garden Centre, Kenilworth Road
Hampton-In-Arden, Solihull, B92 0LW
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