Grow lighting basics…

What is photosynthetically active radiation? What is PAR?

Plants use the range of the light spectrum known as photosynthetically active radiation. Photosynthetically active radiation (PAR) is light in the wavelength range of 400 nm (blue) to 700 nm (red). Plants use all of the PAR spectrum at different stages of growth.

Grow lighting basics. Photosynthetically active radiation (PAR). PAR is the range of the light spectrum used by plants to photosynthesise and grow

What does photosynthetic photon flux mean? What does PPF mean?

All light consists of small packets of energy called photons.

The number of photons emitted by a light source in the PAR range is known as the photosynthetic photon flux or PPF. A unit of measure for a large number of photons of light is called a micromole (μmol).  PPF is measured in µmols/sec.

PAR photons are converted by plants into chemical energy in a process called photosynthesis.

Grow lighting basics. Photosynthesis is the process where plants convert light energy, carbon dioxide and water to produce glucose and oxygen

What is photosynthesis?

Photosynthesis is the process used by plants to convert photons of light and carbon dioxide into chemical energy (glucose) used for growth and development. All that is needed for this process is photons of light in the PAR range, carbon dioxide (CO₂), nutrients, and water.

What is PPFD?

The amount of PAR photons reaching your plant canopy is measured in micromoles per square metre per second.

This measurement is known as photosynthetic photon flux density or PPFD and the units are µmols/m²/sec.

More PAR photons to plants (PPFD) = more plant growth

Grow lighting basics. Photosynthetic photon flux density or PPFD is the amount of PAR photons reaching a one metre squared area per second. It is measured in µmols/m²/sec
Grow lighting basics. The graph charts the relationship between PAR intensity or PPFD and growth rate. The PAR intensity should be between 500 and 1000 µmols/m²/sec range for high growth and high yield.

How much PAR light do I need for my grow area?

To optimise your grow it is recommended that your plants receive 500-1000 µmols of PAR light for every m² (PPFD). Less than this and growth rates will be low. Higher PAR intensity for your plants than this and the increase in growth rates do not justify the extra energy cost.  The plants require additional CO₂ to utilise very high PAR intensity.

What is McCree’s action spectrum and relative quantum efficiency?

In the 1970s a scientist called McCree determined the wavelengths of light a plant can absorb. He assessed the relative quantum efficiency of different wavelengths of light on photosynthesis. In other words he recorded the rate of growth of plants exposed to each wavelength or colour of light.

McCree discovered that plants use all parts of the PAR spectrum but at different rates. The quantum efficiency for red is close to 100% efficient whereas blue and green were less efficient, ranging from 65% to 75%. McCrees action spectrum identifies what colors of the visible spectrum are best for photosynthesis. McCrees action spectrum is often used as a basis for assessing the suitability and effectiveness of a grow lights spectrum output.

Grow lighting basics. In the 1970s a scientist called McCree measured the relative quantum efficiency of different wavelengths of light on photosynthesis. In other words he recorded the rate of growth for each wavelength or colour of light. McCree discovered that plants use all parts of the PAR spectrum but at different rates. The quantum efficiency for red is close to 100% efficient whereas blue and green were less efficient, ranging from 65% to 75%. McCrees action spectrum is often used as a basis for assessing the suitability and effectiveness of a grow lights spectrum output.
Grow lighting basics. A full spectrum grow light contains all colours of light from the photosynthetically active radiation or PAR range. The light frequencies or colours range from blue to red. A full spectrum grow light is suitable for growing your plants from seedlings to flower. MIGRO is full spectrum grow light and is a ‘warm white’ colour to the human eye, comfortable to use and ideal for inspecting your plants health.

What is a full spectrum grow light?

A full spectrum grow light contains all colours of light from the photosynthetically active radiation or PAR range. The light frequencies or colours range from blue to red. A full spectrum grow light is suitable for growing your plants from seedlings to flower. MIGRO is full spectrum grow light and is a ‘warm white’ colour to the human eye, comfortable to use and ideal for inspecting your plants health.

What is a PAR map?

The grow area is divided into a grid and the grow light is hung at its optimum height. A measurement is taken with a quantum meter of the PPFD in each square on the grid. The average and total PPFD across the grow area can be calculated in this way. The information can then be represented as a PAR intensity map to show the PAR levels across the grow area.

Grow lighting basics. The PPFD or PAR measurements are taken across the grow area. The average and total PPFD reaching the grow area can be calculated.

Each PPFD measurement is then translated into a PAR intensity map so that you can visually see how well the light covers the target grow area.

The PAR intensity map shows the PPFD levels across the grow area
Grow lighting basics. The PAR intensity map for a single concentrated light source will provide high intensity of PPFD under the grow light but little at the edges. This will result in hot spots, poor light penetration and uneven growth

What is grow light coverage?

A single and concentrated light source will  provide intense PPFD levels directly under the light. This will encourage the plants to compete and all grow towards the light, blocking each other out.

Grow lighting basics. Multiple light sources spread the light across the plant canopy and result in even coverage, no hot spots and high light penetration to your grow

Grow light coverage from a spread out light source provides photon intensity from multiple directions (like the moving sun) so plants do not grow towards one point but evenly across the canopy. This results in even coverage, reduces hot spots and stress on the plants.

How close should a grow light be to plants?

Having to maintain a big distance between your grow light and plant canopy reduces the height your plants can grow and prevents you growing in low spaces. HPS, MH and boxed LED grow lights must be positioned from 300mm to 1m (1ft to 3ft) above the plants to avoid hot spots and to provide even coverage

When the light source is not as concentrated the plants can grow close to the light source. When the light source is spread out you can grow up to 150mm or 6in below the light sources without hot spots or plant damage.

What maintenance does my grow light need?

MIGRO grow lights are sealed and require no maintenance. The lights will continue to output 80% of their initial level after 50,000 hours (10 years at 15 hour per day) in compliance with the international test standards, LM-80 and TM21.

Traditional HPS OR MH bulbs and the reflectors must be changed at least every year to maintain 80% of their initial output.

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