Choosing Lights: Get to Know Most Important Parameters
What do the acronyms PAR and PPFD stand for? How to calculate the DLI value? When choosing lights for their grow-op, an uninformed buyer may be left wondering about the overwhelming number of technicalities that are supposed to convince them of the quality of various light sources. What do these abbreviations mean and how do they help us choose the right light for our plants?
Light can be described as electromagnetic radiation of different wavelengths. These wavelengths are divided into the visible and invisible parts of the light spectrum. Our human eye detects light with wavelengths ranging from 380 nanometres (violet) to 700 (red). Likewise, in plants we observe so-called photosynthetically active radiation (PAR), which corresponds approximately to the visible part of the spectrum (400 to 700 nanometres). Electromagnetic radiation (light) in the PAR part of the spectrum provides plants with the energy needed for photosynthesis.
Plants also respond to light in wavelengths that they are not able to employ in photosynthesis. An example: The 'far-red' part of the spectrum (700 to 800 nanometres) promotes stem elongation, although it does not support photosynthesis. With the help of LED grow lights such as SunPro MAMSUN – FAR RED, which boost the grow room lighting with specific wavelengths, we can literally shape the plants according to our wishes.
On the other side of the spectrum, there is ultraviolet radiation (280 to 400 nanometres), which is harmful to most living organisms. In nature, it is largely prevented to reach Earth by the protective layer of the atmosphere. With proper care, UV radiation can be used to disinfect growing space with germicidal lights.
Related: Benefits of UV light in indoor grow-ops
Quantifying the precise amount of light in a grow room can be a tricky task. It is impossible to weigh or simply measure it. Light energy can be defined by photons (imagine particles charged with different amounts of energy depending on which part of the light spectrum they represent). In terms of cultivation, we are most interested in how many photosynthetically active photons (in the PAR part of the spectrum) are falling on our plants.
Manufacturers of grow lights give a PPFD (photon flux density) value for their products that tells the grower exactly how much energy the light is radiating on the growing area. For instance: 1 µmol/s/m2 (micromoles per second per square metre) means a whopping 602.3 quintillion photons per second falling on one square metre.
Our tip: You can measure the PPFD in your grow room with a PAR meter.
Higher PPFD values also mean more energy that can be used by plants in photosynthesis. They would thrive, however metabolic processes have certain limits. Depending on plant’s age and species, the optimum PPFD value in a grow room varies from 200 to 1 000 µmol/s. Nonetheless, some extremely powerful LED grow lights can exert PPFD values several times higher. For example, the Spider Farmer SF2000 and other high-end modern LED lights reach values of up to 2700 µmol/s. With such intensive lighting, it is crucial to fill the air in the grow room with carbon dioxide. Thanks to these methods, professional growers can reach extreme yields.
DLI (Daily Light Inegral) is a shortcut for the amount of photosynthetically active radiation (PAR) absorbed by plants in one daily cycle. The equation for calculating DLI is simple. Just multiply the PPFD emitted by the light by the number of seconds in one light cycle.
Understanding the PPFD and DLI is crucial in order to successfully set up a well-functioning and fully operational grow room. There is no difference whether you are growing a single plant or if you have a whole shed full of plants, you need to bear in mind that too high a DLI will burn the plants and too low could hinder their potential.
Is the wattage of grow lights significant?
Over the years, indoor growers have become used to expressing the power of high pressure grow lights in terms of the number of consumed watts. While people pay for the electricity consumed by the number of watts, not all of it is converted into photosynthetically active radiation (PAR).
For older HPS and MH lamps, a considerable amount of energy is lost in the form of heat and unwanted light spectrum. Modern LED lights are better in this regard and are far more efficient. Would you like to learn more about the benefits of LED technology? Read the article Pros and Cons of LED grow lights.