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What is photosynthesis?

Photosynthesis is a process where plants transform photon (light) energy into chemical energy needed for growth. In contrast to most other living creatures, plants use carbon oxide (CO2), along with water, light, and minerals to fuel their growth and energy needs. They convert this into oxygen and organic compounds. You could say that photosynthesis is the most important factor for most life on Earth since without photosynthesis there wouldn’t be oxygen. The light energy is absorbed by a photosynthetic reaction center, a combination of several proteins, pigments, and other compounds that can be found throughout the plant, but mostly in the leaves. Photosynthesis can be described as the following chemical equation:

6CO2+12H2O+light -> C6H12O6+6O2+6H2O

Where 6 carbon dioxide molecules combine with 12 water molecules and light energy and are then converted into 1 carbohydrate (glucose) molecule and 6 oxygen molecules and 6 water molecules.

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Ultraviolet (UV) light

Ultraviolet (UV) light

Ultraviolet (UV) light falls outside the visible light range, or PAR, between 100 and 400 nanometers. This type of light can be divided into UV-A, UV-B, and UV-C.

UVA lies between 320 – 400 nm and is also called Near UV
UVB lies between 290 – 320 nm and is also called Middle UV
UVC lies between 100 – 290 nm and is also called Far UV

The correct implementation of Ultraviolet light can have many benefits. Fighting diseases (such as Mildew) and better smelling and tasting produce are among the benefits of UV light. UV light will help initiate and strengthen a plant’s physical and chemical defense mechanisms and antioxidants including terpenoids, alkaloids, lycopene, anthocyanins, trichomes, phenols, quinones, carotenoids, beta-carotene, and glycosides. These compounds protect your plants, since most of them are toxic to insects and disruptive to the DNA of microorganisms found in molds, pathogens, bacteria, and viruses. These antioxidants also influence the physical and nutritional value of plants, making plants more colorful, and taste and smell better! Treating plants with UV light correctly can prevent fungal diseases such as Botrytis (Gray Mold) and Powdery Mildew from further spreading and surviving by up to 99%1, 2.

1 Suthaparan, A. & Stensvand, A. Suppression of Powdery Mildew (Podosphaera pannosa) in Greenhouse Roses by Brief Exposure to Supplemental UV-B radiation. Plant Dis. 1653–1660 (2012).
2 Suthaparan, A. et al. Suppression of Powdery Mildews by UV-B: Application Frequency and Timing, Dose, Reflectance, and Automation. Plant Dis. 100, 1643–1650 (2016).

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Different types of grow light

Different types of grow lights

Home and professional growers have used a different variety of light sources that distribute their light differently. And while some are a big fan of HPS lamps, others swear by LEDs. Horticraft Holland thinks LED has many benefits over other types of light sources, which we will discuss in another article. In this article we want you to meet the different types of lamps growers use.

High Intensity Discharge (HID) lamps

High Pressure Sodium (HPS) lights are the most common type of supplemental grow light for professional greenhouse growers. HPS lights emit a mix of yellow, orange, and red light, making HPS lamps great for the flowering phase, but not so great for the vegetative phase of your plants. Metal Halide (MH) lights are used with HPS since these emit more blue light and are thus useful for the vegetative phase of the plant. HPS lamps produce a lot of light, but also a lot of heat. The bulbs can reach very high temperatures (as high as 450ºC or 842ºF) and lights should not be placed too close to the crops or anything flammable. HPS bulbs have a lifespan of about 10.000 hours and should be replaced every 12 months.

Metal Halide (MH) lights are mostly used during the vegetative phase because MH lamps put out the light in the blue and green range of the spectrum. That’s why you’ll see MH and HPS used in combination, MH will be used during the vegetative stage and when it’s time to flower, the MH bulbs will be replaced by HPS bulbs. Since MH lights are best for the vegetative stage, they are good for growing lettuce and spinach. MH bulbs are filled with a gas mixture of mercury and metal halides (compounds between metals and halogens). To grow with MH bulbs, you will also need a ballast and a reflector. Finding the right ballast is important since it can underpower or overpower the MH bulb. Overpowering the bulb can lead to the bulb exploding. MH lights tend to become very hot and can lead to serious burns of your canopy, but also anything flammable. MH bulbs have a lifespan of around 6.000-15.000 hours and should be replaced every 6-10 months.

Ceramic Metal Halide (CMH) lights have a balanced output, since they have a mix of blue, orange and red light. This makes CMH lights more PAR efficient than MH or HPS lights. Though, HPS still have a better red light output than CMH and are better for the flowering stage. The Color Rendering Index (CRI) of CMH bulbs is higher than MH and HPS bulbs, making your plants appear more realistic with CMH lights. This makes it easier to inspect your plants for diseases and pests, but also for their general well-being and growth. CMH lights have a higher initial cost than both MH and HPS lights, although they will prove to be cheaper in the long run. CMH lights put out a lot of heat and should be handled with caution. CMH bulbs have a lifespan of around 20.000-24.000 hours and should be replaced every 2-3 years.

Fluorescent lamps

Compact Fluorescent Lighting (CFL) is cheap and suitable for small grow areas or a single plant. They can be found in most hardware stores. These types of light are especially great for beginners. The “soft white” and “daylight” color temperature bulbs are best for gardening. The daylight bulbs are good for the vegetative stage, while the soft white is better for the flowering phase. CFL bulbs put out less heat than HPS bulbs and can be placed closer to the plant, making them well suited for seedlings and young plants or any other kind of low-key indoor gardening. However, the light does not penetrate deep into the canopy, making them less suitable for bigger plants and packed grow areas, and as a consequence giving you lower yields. Since the light from CFL bulbs is mostly pointed away from the plant, using a reflector can be useful to direct all light to your crops. CFL bulbs have a lifespan of around 8.000-15.000 hours and should be replaced every 6-10 months.

Light Emitting Diodes (LED)

Light emitting diodes (LED) use a low amount of energy and put out little heat. LED lights are made up of many small diodes and each of these can be customized to put out a specific color wavelength. This means that LEDs can be customized to a full spectrum, making them ideal for every stage of the plant life cycle. LEDs have better penetration than CFL bulbs and their light can be directed better. LEDs produce a lot less heat (usually less than 80ºC or 176ºF) and direct a lot less infra-red radiation towards your plants. Although LED grow lights are the most expensive option, they are far cheaper in the long run, since you will need less climate control, pay less for energy consumption, get higher yields and their lifespan is significantly longer. LEDs have a lifespan of around 50.000 hours and should be replaced every 5 years. 

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What is light

What is light?

Light can be described as electromagnetic energy or waves moving from one point to another. Each wave for a certain wavelength looks the same; it has the same beginning and ending, and the same height and width. Some wavelengths are shorter, meaning faster wave formation, while other wavelengths are longer (slower wave formation).

The whole range of light wavelengths is called the light spectrum. Wavelengths are measured in nanometers (nm), which is equal to one thousand millionths of a meter (10^9). For example, ultraviolet light lies between 100 and 400 nanometers, while red light can be measured around 680 nanometers.

That particular band of light that growers are especially interested in is PAR or Photosynthetically Active Radiation. PAR light lies between the range of 400 and 700 nanometers and is also called “visible light”. Plants use PAR light for photosynthesis or growth.

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Photosynthetically Active Radiation

PAR stands for Photosynthetically Active Radiation. PAR includes the light ranging from 400 to 700 nanometers that plants use for photosynthesis. The amount of PAR is expressed as the number of micromoles (µmoles) of photons being emitted by the light source.

PAR can be used in determining the strength and overall quality of a grow light. However, it is important to note that the amount of PAR alone is not enough. With a single PAR amount, we still don’t know how much light actually reaches the plant. It is therefore important to also know the position and distance of the light relative to the plant when determining the strength of the light fixture. 

While most plants absorb and use a lot of Blue and Red light, Green gets reflected and this is the reason why most plants look green. This does not mean that plants only need Blue and Red light. Plants use all light wavelengths for different purposes, even light outside of PAR (such as Ultraviolet and Infra-Red light) are useful for plants.

Photosynthetic Photon Flux

PPF is short for Photosynthetic Photon Flux. PPF is measured in micromoles per second, or µmol/s. It expresses the number of photons or total amount of PAR emitted by a light source every second. Photons are small particles that carry the electromagnetic energy of light. The PPF value says something about the total light output that can contribute to photosynthesis.

PPF can be measured with a specialized instrument called an integrating sphere. This instrument looks like a big ball. A ray of light gets shined into the sphere, and the spherical form of the instrument will scatter the light throughout the sphere. A detector inside the sphere measures the total amount of photons emitted by the light. 

PPF does not tell you how much of the light actually lands on the plants, but it says something about how efficient a light is at creating PAR.

Photosynthetic Photon Flux Density

PPFD stands for Photosynthetic Photon Flux Density and measures the amount of PAR light actually arrives at the plant. PPFD is the number of photosynthetically active photons that fall on a given surface each second, expressed in µ/m2/s. PPFD is important when it comes to grow lights, since it measures the amount of usable light that falls on a specific location of your canopy and says something about the true light intensity of the lamp. Light is generally brightest in the center of the canopy and less bright towards the edges of the coverage area, the brightness also decreases the further the light needs to travel. The closer your LED grow lights are to your plants, the more PAR light will actually reach your plants. 

PPFD is a difficult metric to measure consistently, since it depends on many variables. Factors that contribute to PPFD are the distance between the LEDs and the plant and the loss of PPF from the vegetation canopy.

A PPFD chart will show the PPFD values of the grow light for certain points and certain heights in a grow area