PAR , PPF , Lux and Lumen . These are terms that we often hear mentioned when talking about indoor lighting. But what exactly do they mean and how can they affect the growth of your plants?

There is still a lot of confusion among growers regarding the understanding of these units of measurement when purchasing lamps for growing indoor plants, which are instead essential for determining the actual luminous efficacy necessary for growth and flowering.

But how to orient yourself in choosing and understanding the technical parameters proposed by the manufacturers of these lighting systems?

A guide on the light spectrum for plants that defines itself as academic cannot fail to have the opinion and explanation of Dr. Alessandro Peretti

Probably among the most competent people on the subject that we have in Italy and beyond.

Report follows in the next paragraph

Which light spectrum do the plant need? Let’s clarify it

In the context of plant lighting, it is essential to understand the concepts of PAR , PPF , Lumen and Lux.

Let's start with lumens, it is a unit of measurement that indicates the total amount of luminous flux emitted by a light source in all directions.

They represent the visible brightness perceived by the human eye (not plants) and are used to evaluate energy efficiency, but do not provide information on the quality of light, such as color or light spectrum.

Lux is a unit of measurement of "illuminance" (Lumens per cm2), which indicates the quantity of light that reaches a specific surface.

They measure the luminous flux density per unit area and depend both on the luminous flux emitted by the source (measured in lumens) and on the distance between the source and the illuminated surface

These units of measurement are expressly used for studies and designs for lighting intended for humans, not for plants.

Plants absorb light differently than the human eye so finally put these 2 units in the attic

To evaluate the photobiological processes in plants, other units of measurement such as PPF (Photosynthetic Photon Flux) and PPFD Photosynthetic Photon Flux Density) come into play.

PPF measures the total flux of photons emitted by a light source that is usable for plant development processes. This unit of measurement takes into account all wavelengths of light emitted by the source and provides an estimate of the total amount of light energy available for photosynthesis.

The unit of measurement is μmol/s (micromoles of energy / per second)

PPFD, measures the amount of photosynthetically active photons reaching a specific surface at a given time. This unit of measurement takes into account the area on which the light falls and indicates the intensity of the light that the plants actually receive.

Units of measurement are μmol/s/m2 (micromoles of energy / per second on a surface of one square meter)

Let's try to understand how to choose the light source that's right for you.

we explain a fact that you will certainly have read about during your research and which is increasingly highlighted by the various manufacturers of LEDs for cultivation , namely THE EFFICIENCY expressed in μmol/J or μmo/W.

This measurement indicates the amount of photosynthetically active light that an LED emits for each watt of electrical energy consumed.

A more efficient LED will produce more light using less energy, resulting in a better yield for plant growth and photosynthesis.

But watch out for scams here too! These values ​​can be "altereted". .. a FULL SPECTRUM LED will have a very high efficiency, but this does not mean that it is really that efficient. These LEDs emit a lot of light in the green-yellow area, this light is measured by the photon flux meter in the PAR spectrum (400-750nm), but in reality it has no particular effect on plant growth.

This waste of energy in the yellow and green colors can reach up to 20-25% , leading to the advertised efficiencies being reduced by up to a quarter and energy costs rising by a quarter.

So in the last element it is also necessary to evaluate, in addition to the efficiency, also the type of spectrum emitted by the lamp, since if too unbalanced in the yellow-green area it will produce more waste and less effect on the plants

How does light affect indoor plant growth?

We have often told you about chlorophyll photosynthesis , one of the vital processes of plants, in which light plays a fundamental role.

Sunlight, water and carbon dioxide are synthesized by plants to create energy and release oxygen. This process occurs in the chloroplasts , where chlorophyll (the pigment that gives plant species their classic green color) is present .

But what types of light are necessary for healthy and prosperous plant growth?

And this is where La PAR comes in. acronym for active photosynthetic radiation, i.e. the portion of light useful for plant growth.

Since light is made of luminous particles called photons, their intensity, quantity and color strongly determine the development of plants.

Light, strictly speaking, is electromagnetic radiation composed of a visible part of the spectrum and a part invisible to the human eye.

The red and blue light of the visible spectrum are both essential for the correct development of plant growth because they serve to fix carbon dioxide and create sugars used by the plant to produce energy.

However, when we refer to the light spectrum, we are usually talking about wavelength rather than color.

The spectrum of solar radiation, in fact, extends over a wide range of electromagnetic wavelengths and can be divided into ultraviolet (UV), visible light and infrared (IR).

Infrared and ultraviolet rays, invisible to the human eye, are essential for the maturation and growth of flowers. LED grow lights , for example, have greatly increased the quantity of these useful spectrums for plants

The spectrum visible to humans (the quantity of which is expressed in Lumens ) represents a minimal part - less than 1% of the electromagnetic spectrum - and extends from wavelengths from approximately 380 nm to approximately 750 nm . including various colors of the chromatic spectrum:

  • Purple : 380-435 nm;
  • Blue : 435-500nm;
  • Green : 500-555nm;
  • Yellow : 555-600 nm;
  • Red : up to approximately 750 nm.

Plants perceive light differently than the human eye and need a very small fraction of visible light for their development process.

Thanks to specific photoreceptors (called phytochromes ) sensitive to different wavelengths, they receive information from the light spectrum they absorb. And they react almost instantly, stimulating and activating processes necessary for their development.

Knowing the relationship between different wavelengths and the metabolic responses of plants allows the grower to influence the characteristics of the plants he grows, such as shape, nutritional values, taste and flowering time.

WHAT ARE THE UNITS OF MEASUREMENT OF LIGHT AND WHY ARE THEY IMPORTANT IN LIGHTING INDOOR PLANTS?

As a grower, you have a lot to think about. Plant life cycles, grow light location, light spectrum, growing space:

These are all incredibly important factors to consider when building a greenhouse for indoor plant lighting.

In this regard, you will have realized that mysterious acronyms - PAR, PPF, PPFD - alongside terms such as Watt, Lumen, Lux determine the efficiency and power of the lamps

All these metrics and units of measurement of light are fundamental in indoor cultivation, because they allow you to evaluate the quantity , quality and power of the optimal light to provide to the plants.

So let's see in detail what exactly these terms mean and which ones you should most take into consideration.

PAR light (photosynthetic active radiation)

Let's immediately explain “what is PAR?” . This is an acronym that stands for “Photosynthetically Active Radiation” .

Since, as we have seen, plants only use specific colors or wavelengths of visible light, we can more simply define PAR as that part of light radiation that is truly useful for plant growth, included in the range of 400-70 0nm .

PAR is not a unit of light measurement , rather it is a term that can help the grower determine the type and volume of light needed to optimize plant performance and health.

When trying to choose plant lights , always make sure you understand

  1. how much PAR the lamps produce;
  2. how much energy they consume to produce PAR;
  3. how much PAR is actually available to plants.

These three parameters will help you opt for the best grow light. And remember that to measure PAR, you must have a specific meter or a spectroradiometer with a sensor calibrated to detect the amount of photosynthetically usable light.

lux and lumen

The appearance and spread of LED lamps and bulbs has meant that terms such as lumen and lux have become frequent in common language, however generating quite a bit of confusion about their meaning.

Essentially, Lumen and Lux ​​are units of measurement of light , used to describe quality and quantity respectively. Let's try to understand them better.

To check the efficiency of your lamps and their degradation over time, you can use a tool like the Milwaukee MW700 Luxmeter

  • Lumen (lm) : measures the light power emitted by a light source. That is, it describes the total quantity of visible light emitted by a light source. It is a linear unit of measurement, which does not take into account either the path the light takes or its distance from what it must illuminate;
  • Lux (lx) : measures the illuminance, i.e. the quantity of visible light that reaches a surface and is measured in lumens per square meter (lm/m²). It expresses exactly how much light there is in an area and how it is distributed at a certain distance from the light source.

PPF (photosynthetic photon flux)

PPF is an acronym for Photosynthetic Photon Flux , which can be literally translated as "photosynthetic photon flux" .

This is an important parameter for evaluating a lamp for growing plants, as it defines the measurement of the PAR .

This value, in fact, determines the quantity of photosynthetic photons released (i.e. how much PAR) per second by a light source and is measured in micromoles per second ( μmol/s ).

High amount of light emitted by a lamp corresponds to a high PPF value. However, although this number is an important metric for comparing different light sources, it alone is not enough to evaluate the real effectiveness.

The reason is simple: the PPF tells you how much light a lamp can generate in the PAR space between 400 and 700 nm, but not how many of these photosynthetically active photons are then actually absorbed and used for photosynthesis.

PPFD (photosynthetic photon flux density)

Photosynthetic photon flux density ( PPFD) measures how many photons from the PAR region impact a specific area in one second.

It is measured in micromoles per square meter per second ( μmol/m²/s ). In short, if you want to know how much light is actually emitted and how many of the PAR photons are used by the plant, you have to measure the PPFD.

You can measure this using a spectrum meter , and to really be sure your grow lights are working at their best, it's important to continuously measure the parameter at different heights and areas of a plant's canopy.

The problem with using the PPFD as a reference value is that its reading can be influenced by various factors, such as the distance of the plants from the light source and the density of the light.

Reflections from the ground and walls of an area and the ambient temperature also play a huge role in influencing the measured values.

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