Lighting

Lighting is the most important aspect of growing consuming the majority of power and being the most expensive single component in the grow system.

The energy produced by the sun reaches the earth as electromagnetic radiation. Light and other forms of electromagnetic radiation are considered to have both a wave nature and a particle nature. Particles or packets of light (its particle nature) are known as photons - the smallest divisible units of light. The brightness of light depends on the number of photons absorbed per unit time. Each photon carries a fixed amount of energy which determines the amount that the photon vibrates. The distance moved by a photon during one of it vibrations is referred to as its wavelength and is measured in nanometers. Sunlight contains 4% ultraviolet radiation, 52% infrared radiation and 44% visible light.

The portion of the light band most responsible for photosynthesis measures 400-700 nanometers. This band is often termed the Photosynthetically Active Radiation (PAR). Within this range, intensity is the most critical factor along with light period. Within the PAR region light is measured as the Photosynthetic Photon Flux (PPF) and is expressed in µmol/m2/s. Daily total of PPF, expressed in mol/m2 have been shown to relate to total photosynthesis for the day.

Photosynthesis is the key to good growth and high yields. If photosynthesis is decreased due to low light conditions environment conditions (which closes stomates and reduces gas exchange) or water stress then the production of sugars will decline and the quality, shelf life and size will all diminish.

Photosynthesis is the process by which plants capture energy from light to produce their food and build their tissues. Not all light is equal however. Certain wavelengths and colors are crucial for this process and certain others actually inhibit it. As a result choosing the right colors of light is vital for any horticultural use.

Photosynthesis is a multi-step process that requires light, carbon dioxide (which is low in energy), and water as substrates. After the process is complete, it releases oxygen and produces glyceraldehyde-3-phosphate (GA3P), simple carbohydrate molecules (which are high in energy) that can subsequently be converted into glucose, sucrose, or any of dozens of other sugar molecules. These sugar molecules contain energy: the energized carbon that all living things need to survive.

Photosynthetic organs of a plant contain an assortment of pigments they can be divided into three major classes. These pigments exist, each of which has evolved to absorb only certain wavelengths or colors of visible light. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color.

Chlorophylls

Carotenoids

Phycobilins

There are five major chlorophylls: a, b, c and d, along with a related molecule found in prokaryotes called bacteriochlorophyll all serve similar functions. For normal plants chlorophyll A and chlorophyll B are the main workhorses of photosynthesis. Chlorophyll A is situated in the light-harvesting complexes (LHC) the core antennae as well as the reaction centers and uses a range of light colors with peaks at approximately 430nm and 662-700nm blue-violet region. Chlorophyll B is only found in the light-harvesting complexes (LHCs). And uses a similar range with peaks at approximately 453nm and 642-680nm red-blue region. Neither a or b absorb green light; because green is reflected or transmitted, chlorophyll appears green

Chlorophyll D serves a similar function. There are also auxiliary pigments which use smaller sections of light. These include beta-carotene which uses small sections of the blue violet range.

Carotenoids are a much larger group of pigments. In photosynthesis, carotenoids function as photosynthetic pigments that are very efficient molecules for the disposal of excess energy. When a leaf is exposed to full light, the light-dependent reactions are required to process an enormous amount of energy; if that energy is not handled properly, it can do significant damage. Therefore, many carotenoids are stored in the thylakoid membrane to absorb excess energy and safely release that energy as heat. Carotenoids absorb light in the blue-green and violet region and reflect the longer yellow, red, and orange wavelengths.

Phytochromes are a type of pigment found in plants. The plant uses these pigments as photoreceptors to detect changes in light. There are two main forms of phytochrome Pr and Pfr. The first one responds primarily to red light and the second responds primarily to far-red light. Pr is transformed into Pfr following the absorption of red light. Likewise the absorption of far-red light transforms Pfr to Pr.

One of the functions of the phytochromes is to determine the amount of shade over the plant, especially the amount of shade produced by the leaves of other plants. Under normal circumstances natural light contains both the red and far-red parts of the spectrum. As the light filters down through leaves more and more of the red light is taken out because it is absorbed by those leaves for photosynthesis. This decreases the ratio of red to far-red light causing the plant to expend more of its energy to grow taller to get above the perceived canopy instead of producing more leaves. A plant in this situation will also put more of the leaves it does produce at the top of the stem in order to make use of the greatest amount of red light.

The wavelengths included in the far-red region are those that are in the range of 650 to 800nm although the cutoff point is closer to 740nm.

Robert Emerson discovered several surprising things about photosynthesis called the Emerson Enhancement Effect. Being the enhancement of the quantum yield of a photochemical process produced in plant cells by far red light and by simultaneous illumination with light of shorter

wavelengths (red light). The results of photosynthesis are greater if there is a combination of red and far - red light than if there was an equal amount of light that was only red or only far -red.

The "red : far red ratio" is a comparison of the amount of red light relative to the amount of far red light that is shining on a plant's leaves. For optimum photosynthesis both red and far red light must be available to the plant. However too much far red light will cause problems.

The red wavelengths are in the range of 600 to 650 nm and is the most effective kind for photosynthesis.

The blue region of light has a range of 400 - 520nm. Experimental evidence is clear that blue light is required for photosynthesis. If there is sufficient blue light the size of the leaves will be good. It is a factor in the development of the chloroplasts. Chloroplasts are the parts of the leaf's cells which contain the chlorophyll and conduct photosynthesis so they are important.

The middle of the spectrum between 520 and 650nm. The green and yellow colors in this region are not used much by the majority of plants. They are reflected away which is what gives chlorophyll ( leaves ) its green appearance. Many kinds of plants have secondary light absorbing pigments which make use of the light in this range such as beta – carotene. Red and blue light doesn't not penetrate far into the inside leaves as far as green light can as they are absorbed. The leaves of many species of plant contain more than one layer of photosynthetic cells (chloroplasts), and strong green light would add more energy to photosynthesis in these cells than the usual red and blue lights.

If there is a reason to encourage the stomata of the plants to open, extra blue and red light is useful. Extra green light will encourage the stomata to close. Adding green light to an already complex mix of reds and blues can help to expand the leaf area.

Ultra - violet light is divided into three ranges: UV - A, UV - B, and UV - C.

UV - A is the closest to visible light, with a range of 315 - 400nm.

UV - C is the farthest from visible light, at 200 - 290nm.Very little UV - C radiation makes it past the outer atmosphere, so it is not generally seen as important for horticulture.

UV – B holds the middle ground between them, at 290 - 315nm.

UV light causes problems for plants much as it does for humans. The beta carotene in some plants provides some protection from UV light but generally speaking all UV light will affect photosynthesis. Chloroplasts are particularly damaged by over exposure to UV.

UV – B can be used to stress a plant to increase Phytochemicals.

The basic chemical formula that

describes the photosynthetic reaction:

6CO2 + 6H2O ------> C6H12O6 + 6O2

Where: CO2 = carbon dioxide

H2O = water

Light energy is required

C6H12O6 = glucose

O2 = oxygen

oxygen

Therefore, according to the chemical equation for photosynthesis carbon dioxide and water produce sugar and oxygen when exposed to light. Although this equation looks simple, the many steps that take place during photosynthesis are actually quite complex.

Photosynthesis takes place in two sequential stages: the light-dependent reactions and the light-independent reactions.

In the light-dependent reactions, energy from sunlight is absorbed by chlorophyll; that energy is converted into stored chemical energy in the form of NADPH (nicotinamide adenine dinucleotide phosphate) and ATP (adenosine triphosphate). Protein complexes and pigment molecules work together to produce both NADPH and ATP.

LED Lighting

In the light-independent reactions, the chemical energy harvested during the light-dependent reactions drives the assembly of sugar molecules from carbon dioxide. Therefore, although the light-independent reactions do not use light as a reactant, they require the products of the light-dependent reactions to function. In addition, several enzymes of the light-independent reactions are activated by light. The light-dependent reactions utilize certain molecules to temporarily store the energy: These are referred to as energy carriers. The energy carriers that move energy from light-dependent reactions to light-independent reactions can be thought of as “full” because they are rich in energy. After the energy is released, the “empty” energy carriers return to the light-dependent reaction to obtain more energy.

There are many manufactures producing LED'S but not many that produce LED'S for horticulture use. Normal blue and red LED'S are not in the right colour spectrum as they are at a wave length of 420 nm and 620nm where the best for optimum growth is at 450 nm and 650 nm. As the demand for these LED'S is not great there are a few manufactures, making the cost of these LED'S very high.

The Main Requirements Are:

•Good coverage with good intensity

•Good color ratio.

•Even lighting throughout the grow area.

•Low energy consumption.

•Easy to install and maintain.

•Cheap.

•Small profile.

•High quality

Color measured in wave length, plants only use a certain wave length of light these are predomtidly 450 nm and 650nm this is then know as the PAR spectrum other colors have very little effect and are used sparely.

Color ratio is critical in producing a quality product. A general color ratio of 8 to 1 works best for general growing promoting a great quality product that is dense and has weight Sometimes White light is also added making visible sight for the operators to see.

Power is important as electricity is costly and this does not lend itself to compare lights such as a 40 watt grow lamp to a 10 watt led light as the intensity of the light source is critical in been able to supply the amount needed to the correct location i.e. the plant

Beam angle each led light has a different beam angle and this determines the area that can be covered not forgetting intensity drops with wider beam angles and care has to be taken that the correct color ratio is still obtained

Heat dissipation there are a number of methods of connecting LED’s to a power source some generate more heat than others as there is always heat generated when converting one energy form to another such as electricity to light been able to generate the minimal heat and disperse this heat uniformly and evenly is critical. If not consider the life span of the light will be shortened.

Intensity is also very important if not enough intensity is achieved poor growth results in a poor quality product. Light emitted from a led does not travel very far, in fact, the intensity drops dramatically in a very short distance. It has been found that good growth is achieved with 200 µmol or more. When it comes to growing with led’s it is very difficult to achieve this.

Intensity And Beam Angle two examples are shown above at the top of slide of the two types of led’s the intensity is measured in mcd (milli-candela). The narrower the beam of light the greater the intensity. The further the distance the less intense is the light.