Lighting In Hydroponics

Lighting for hydroponics

Herbivores then eat the plants to consume some of that delicious synthesised energy, and carnivores eat the herbivores. I’ve just written your biology essay, you’re welcome.

Hopefully, we’re all aware white light is made up all the colours of the rainbow, Issac Newton demonstrated this in 1665 with the use of a glass prism. Each colour occupies a specific wavelength on the electromagnetic spectrum, of which there is an important biochemically active range available to plants.

The light intensity for plants is coined the photosynthetically active radiation (PAR). Only within this range of 400 to 700 nanometers can plants produce the sugars necessary for survival. Photons of shorter wavelengths than 400nm carry too much energy which would damage the plant’s cells, they’re naturally absorbed by the ozone layer. Longer wavelengths than 700nm don’t have enough energy to stimulate photosynthetic reactions.

There are variables which affect the PAR such as seasonal changes in Earth’s distance from the Sun, altitude, and cloud covering. Anything potentially altering natural light intensity.

You can measure PAR from artificial light sources. The inverse-square law states if an object is double the distance, it’ll receive one-quarter the radiation and is a challenge indoor growers must navigate. Hence why reflectors are utilised to maximise efficiency.

PAR meters measure the intensity of light within the wavelength range necessary for photosynthesis. Simply place your meter near the leaves to figure out what they’re absorbing.

Not all PAR meters necessarily measure within exactly the same range. Some could record between 400nm and 700nm and others between 300nm and 800nm. So, if one lamp has an output between 350nm and 750nm, the meter measuring a bigger range will record a higher PAR, however, a portion of this wavelength is irrelevant to the plant’s growth.

At the blue end of the spectrum, photons carry more energy. Red light carries approximately half that, yet the PAR meter records each photon the same as long as it’s within the correct wavelengths.

So, you can have a red bulb and be amazed by the high PAR reading, but actually, the energy output is minimal. If the energy output isn’t that high, your plants won’t grow as much.

Right, PAR measures light intensity but not necessarily the quality of the light being received. The meter records in micromoles (µM) and will record 0µM if no light is reaching the instrument. The approximate maximum plants enjoy 1500µM

Plants which have a broad spectrum of light across all wavelengths are healthier, and more structurally sound. Makes sense, natural light contains all wavelengths which plants have evolved to utilise.

The intensity of your bulb needs to strike a balance between light reaching the plant, and heat generated to its surrounding areas.

If the light doesn’t carry enough energy, the plant will concentrate its growth to become taller to maximise photosynthesis. This is a needless waste in the potential growth of large leaves or fruit to start bearing.

Too much heat will disrupt essential biochemical processes and your plant will, unfortunately, die altogether.

Fluorescent Lights

Fluorescent lights work by sending an electrical discharge through mercury gas within a bulb. Excitation of the mercury vapor releases ultraviolet light which interacts with a phosphor coating lining the inside of the tube, causing it to glow.

Fluorescent lighting remains the most popular type of lighting for hydroponic growers. They’re as cheap as incandescent bulbs but are massively more efficient.

There are two types, compact and tubular.

Tubular fluorescent lights are straight and long, and the thinner the diameter the brighter the bulb. Their reduced surface area results in a more intense fluorescence.

Compact fluorescent lights are smaller and have tubes which are twisted over, they’re the ones replacing incandescent bulbs in our homes. Other than that, compact fluorescent lights basically the same as tubular.

The naming of tubular fluorescent lighting begins with a T, representing the tubular structure. Alongside the T is a number, for example T5, which corresponds to the size in diameter.

T5 bulbs are designed for use for artificial plant growing, however, people do regularly utilise T8s, too.

A fluorescent lighting advantage is low heat output so you can - and should - place the lights closer to your plants for more energy to reach them.

Less waste heat energy means you can save money avoiding buying ventilation systems, and your plants can be packed into a tighter area for greater yield.

CFLs are widely available at many kinds of shops including supermarkets, making them great for beginners as well as having no additional technical components to incorporate into the setup.

Fluorescent lights do have drawbacks, including a lower intensity of light than HIDs so your plants won’t grow as fast. Being closer to the plants means you’ll have less room for error, so regularly checking everything’s in working order is necessary, if tedious.

Fluorescent Bulb

LED Lights

Light-emitting diodes (LED) are two-lead semiconductor light sources. A lead is an electrical connection between a wire and a metal pad.

They work using a p-n junction, which acts to control the direction of electrical flow in a circuit. The ‘p’ side has an abundance of positive impurities and the ‘n’ side of the junction an abundance of negative impurities.

The disbalance of electrons towards negative half of the junction causes an electrical flow towards the positive end as the electrons fill the void in the electron-less positive impurities, termed electron holes.

Recombination of electrons and electron holes releases photons, the colour is determined by the energy gap the electrons travel.

LEDs are very efficient, using even less electricity than fluorescent lighting, and with it produce less heat waste so their bulbs last a lot longer at an estimate of 10,000 hours.

The cost of buying LED units can cost a lot, however, similarly to fluorescent lights, they make their money back in electricity bill savings.

LEDs can be tailored to produce the wavelength you desire. Studies have been conducted with different colours of LEDs on plant growth.

Red-only LEDs typically yielded unhealthy plants, but supplementation with blue light produced more optimal growing results. What’s really interesting is crop yield is even higher when red LEDs are supplemented with blue and green LEDs.

If anyone suggests green light doesn’t affect plant growth, they’re incorrect.

I hope we can all agree NASA is a reliable source. They determined LEDs were the best light source for indoor plant growth.

Red light, wavelengths of 630nm to 660nm, appeared to be essential for stem growth, and leaf expansion, as well as flowering regulation, dormancy, and germination of seeds.

Researchers concluded blue light, wavelengths of 400nm to 520nm, needed to supplement other colours for best results. Too much blue light may affect growth of some plant species, additionally, abnormal chlorophyll concentrations and leaf thicknesses.

Green light, wavelengths of 500nm to 600nm, is necessary for penetration of the canopy top to reach plants on the ground.

Red light at the very furthest of the spectrum, wavelengths of 720nm to 740nm, also penetrates through the canopy above and initiates larger leaf span. Furthermore, infrared light appeared to speed up flowering times.

A lot of LED light systems come with their own cooling mechanisms and can be plugged directly into the wall and hung up for immediate use.

LEDs should be kept further away from plants than fluorescent lights meaning a higher growing space may be necessary if you’re starting out in a confined area.

High-Intensity Discharge

As you can imagine, high-intensity discharge (HID) lights have high lumen-per-watt efficiency.

There are several different types of HID available, but each needs a ballast to function properly. Ballasts regulate the amount of current drawn into the bulb, without them the bulb would immediately blow if connected to a source with high voltage.

Nowadays ballasts allow for the changing between different types of bulbs, but it’s something you should double check before purchasing.

HID lights are normally reserved for serious growers, or those growing commercially. They’re expensive and your electricity bills may skyrocket, but the light intensity and quality of spectrum make them, technically, the best lights for growing plants.

HID lights have a higher luminosity because a larger percentage of their total radiation is within the visible light range of the electromagnetic spectrum compared to infrared. With that intensity comes a lot of waste heat. You’ll need a good ventilation system to combat this so your plants continue to live the sweet life they’ve come to know.

There are two main types of HID lights, metal halide (MH) and high-pressure sodium (HPS).

Metal halide lamps create an electrical arc through a mixture of mercury and metal halide gases. The metal halides are typically iodine and bromine compounds, with the most common of those used being sodium iodide.

When comparing the bulb shapes of MH and HPS you’ll notice MH bulbs are fatter at their thickest point whereas HPS are long and thin.

There are two types of pressurised sodium-vapour lamps, low and high pressure. The low pressure is efficient but produces a yellow light and its application is usually limited to street lighting. High pressure results in a broader spectrum of white light.

Either MH or HPS can be used for the plant’s lifetime. However, MH lights are typically used during the early vegetative growth phase and HPS for later in the plant’s life when it begins to bear fruit and flower.

MH lights produce a slightly blue light which imitates the spring through to the early summer sun, the HPS light is more orange for the late summer to autumn sun.

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