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What do you need to know to be a good Grow Light Tester?

Growing plants indoors demands the use of artificial light sources that guarantee the necessary lighting for the growth of your crop. Acquiring the lights is just the first step, since as every Grow light tester knows, there are even more important factors, such as the quantity and quality of the lighting that your plants receive. Therefore, today we will give you some tips so that you can also become one.

Lighting intervenes in all the processes of your crop, from the plants being in the seedling phase to flowering and fruiting. Through lighting adapted to the true needs of your plants and the conditions of the space, you can significantly increase the yield of your crop.

Controlling the conditions and studying how each variable impacts your crop could give you a considerable competitive advantage over other growers.

In that sense, having a real knowledge about the performance of the lighting system you are using and knowing to what extent your plants are benefiting from the light you are providing them, will allow you to make the right decisions, at the right time.

As a Grow light tester you will have the ability to diagnose the deficiencies in the lighting of your crop, and find the most appropriate solutions.

Therefore, throughout this article you will find information that will help you become a good grow light tester and get the most out of your lighting system. To do this, below, you will find some key concepts and indications on how to perform field tests.

A good Grow light tester: you need to know about PPFD, PAR and PPF

First of all, every good Grow Light tester should handle some basic terms that allow you to thoroughly understand the operation of your lighting system. This will guarantee a successful measurement and will be what will provide you with useful information to evaluate the lighting quality of the crop and its yield success.

To introduce the terms that will be developed below, the first thing you should know is What is a photon?

Photons are particles (tiny and elementary) that make up light. In other words, they are particles carrying the light energy that is visible. Photons are credited with being the ones that generate magnetic and electric fields.

Now that this has been clarified, you will be able to understand the importance of photons in grow light tests. To do this, we will start by defining the terms PPFD, PAR and PPF, pay close attention to the following sections.

What does PPFD, PAR and PPF mean and imply?

As you may already know, there are wavelengths for each color of the visible spectrum of light, which are used by your plants in each of their processes. Although useful, this knowledge is not enough for a grow light tester, since you will also have to learn about other terms and measurements that will allow you to know the real and exact amount of light that reaches your plants. Below, we will explain the most important terms with which you should familiarize yourself as a new grow light tester.

  • PAR (Photosynthetically Active Radiation): PAR could be considered a parameter that relates to the number of wavelengths (radiation) that trigger photosynthetic activity, that is, the amount of light needed to stimulate or induce photosynthesis in your plants. This includes all photons that fall into this range and is expressed in units of energy (Watts/Joules). Par is in a visible wavelength range of the spectrum between 400 to 700 nanometers.  
  • PPF (Photosynthetic Photo Flux): THE PPF allows us to know that the amount of light in photosynthesis is composed of the number of photons within the PAR interval. That being the case, the PFF will help you know the total number of photons per second that come out in a PAR wavelength range. This measurement allows you to describe the amount of photons emitted by the light source you are using in your crop.
  • PPFD (Photosynthetic Photon Flux Density): this measure in addition to including everything mentioned in the PPF, also measures the flux density of photons on a particular surface. In the case of crops, it allows you to know the number of photons (per second) that under the PAR range collide or reach the surface of the leaves of your plants (canopy).   

Now we will move towards some metrics that will be important for the application of these new concepts.

Metrics that are important to know

Each of the terms mentioned above will allow the testing and measurement of lighting in your crop, and are the ones that will shed real light on the efficiency, the coverage area and the true harvest potential that your crop will have, from the capacity of the light source used and the conditions of the environment.

PAR light is measured using a photovoltaic detector, which has sensors that detect light and measure it in millimoles of light (per square meter). This value usually ranges from 0 to 3,000 mmol and is commonly measured through photon flux density (PPFD).


For its part, the PPF is measured in micromoles per second (μmol/s), which will allow you to know the amount of PAR from a specific light source. It will also be useful for comparing yields between one lamp and another.

Finally, the flux density (PPFD) allows to establish the number of photons within the PAR that reach a surface. It is measured in micromoles per square meter per second and is expressed as follows: μMol/m2/S. According to reliable sources, an adequate amount should be found between 600 – 900 PPFD, per square meter.

In the case of your indoor crops, a good fact that you should know about your lamp is the size and area it covers, in addition, you could also ask your grow light supplier about the PPF or PPFD of the lighting device you have acquired or want to acquire (although it will never be as reliable as making the measurement yourself). These measures will be more useful to optimize the yield of your crop, than just knowing the lumens or wattage of the lights you are using.

Perform field tests

For the measurement of PPF in this case, we will focus on field tests (although it is worth noting that there are also laboratory tests.)

Field tests are performed in environments similar to those of any indoor crop. However, you will need to use reflective walls to be able to take measurements in the growing area.

The field test will allow you to know the number of photons that specifically reach the canopy of the grow space and not all the photons produced by a lamp. It is for that reason that this measure is called "usable PPF" of a device.

As a good grow light tester, you will learn that the field test is the most suitable for your indoor cultivation since the amount of photons that reach the canopy of your crop, will be the ones truly used by your plants for the photosynthesis process.

This usable PPF does not represent a constant value. On the contrary, the number of photons that can reach the canopy of your crop will depend on some factors such as: size of area, distance between your lighting device and the crop, and the presence or absence of walls that are reflective.

Once the reflection, coverage area and height of the lighting device have been optimized, you are ready for the next step: measure the usable PPF and find the most optimal one for your crop.

The measurement of optimal photon density (PPFD) should be at an average of 65 μmol of usable PPF per square foot, which is equal to 700 μmol per square meter. For its calculation in square feet you will only have to divide the result of the PPF obtained by 65.

Tips for better results with lighting

Every grower wants to obtain better results in his cultivation and although all the growth lights try to direct most photons towards the canopy of the crop, reality shows that there is always a dispersion of them. Therefore, the importance of reflective cultivation walls arises.

In growing areas of a small size the PPF will also be reduced, while in very large areas the PPF will increase, but the light density (PPFD) will be much lower than expected. The key is to find the balance. But how to achieve it?

It is best that the plants of your crop extend towards the edge of all the walls, since the closer the canopy is to the walls (reflective) the lower the loss of photons. This means reducing reflection or overflow losses.

Another important aspect that you should take into consideration is the height or distance (from the top) between your lighting device and the canopy of your crop. Logically, the closer the lights are to your plants, the more photons they can capture and the farther away, the greater the number of photons lost. This results in the PPF throwing a smaller number when your lamp is farther away.


However, this does not mean that the best option is always to locate the lamps very close to the canopy of your crop, since placing the plant very close to your lamp could cause them serious damage. In addition to burns or stains, thanks to the PPFD study today we know that it could also trigger a photoinhibition that will damage your plant, having been exposed to more than 1000 μmol.

In this way, the usable PPF will allow you to know the ideal height at which you should place your lighting device, knowing that the growth lights must be hung at a height that places the maximum value of the PPFD in an interval between 950 -1000 μmol.

Grow light tester in practice

As explained in the previous sections, you will have noticed that a good Grow light tester must take into account many variables linked to lighting, within its indoor cultivation space. And that any change in conditions (dimensions of space, number of plants, size of lights, type of wall material, distance between the canopy and the lamp) will directly affect your test.

For that reason, you must generate the best possible conditions. In the following lines we will provide you with some recommendations, including the equipment and materials you will need, as well as other resources or recommendations for carrying out your test.

 First, you will need the following materials:

  • Reflective walls of BoPet (Mylar): The reflective walls are made of a material called BoPET (biaxially-oriented polyethylene terephthalate) and you can find it under the trade name Mylar, which is a kind of polyester film that is very resistant and chemically stable, in addition to a high reflective capacity, it is also an excellent electrical insulator.

You should cover the walls surrounding your crop with this material. BoPET can reflect more than 85% of the photons that approach it, maximizing the PPF usable for your crop.

  • Black non-reflective awning: you can use some type of carpet or black material that you can place at the bottom of your test area. This will be done with the intention of simulating the canopy of your crop, because the black color allows the absorption of the photons that impact it.
  • Quantum PAR sensor: this device is the one that will allow you to measure the Photosynthetic Photon Flux Density (PPFD). Once the device is placed in the right place, the photons will impact the sensor and consequently generate an electrical output in mV (millivolts) that will show the number of photons that reach the canopy of your crop. 

Once you have the materials, pay attention to this step-by-step to perform your test:

  1. Organize the area where the test will be done: delimit the area and cover the walls with the reflective material. Your lighting device should be located in the center.
  2. Set the height of your lamp or bulb: To make sure your lights are located at the correct height, measure the PPFD with your sensor, which should reach a maximum PPFD reading (anywhere in the test space) between 950 and 1000 μmol. This will be the optimal height. 
  3. Measure the PPFD: cover the bottom with a black vinyl or carpet and draw grids with cells of equal size. Next, you will have to place the sensor in the middle of each of the boxes. Remember to record the reading obtained for each cell. Then, proceed to add all the results obtained and divide it by the number of cells you drew to get the average PPFD. 
  4. Conversion to usable PPF: Finally, you can convert the average PPFD obtained to usable PPF, by multiplying the density obtained by the area, that is, by the number of square meters of your test area. That will be the optimal usable PPF for your crop. 

Are you ready to be a good grow light tester? Follow these steps and then tell us how it was. If you need any extra queries, you can visit our website and supplement your information.

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