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The Science Behind Indoor Lighting – By Stoney Tark

Growing Cannabis successfully has always been a skill and a science.

The lighting industry is now more advanced than ever before when it comes to science and knowing which of the latest tech does what can be quite confusing and misleading. Weed World Magazine sat down with Martin Anker from SANlight LED to break down the technical aspects of lighting, what plants actually need and his advice and tips when it coming to investing in a new horticultural lighting system.

Hello Martin, as an engineer at SANlight can you tell us more about your role there?

As engineer and C.E.O of SANlight I’m the one with the big overview. That means I’m connecting the botanical research, which is done in house, and the technical engineering together.

How exactly do plants respond to light and what is it they use for photosynthesis?

Plants are using light for photosynthesis as well as for detecting their environment. All photons with a wavelength from 300 nm and 750 nm are detected by the plant. Some colors (wavelength) are used only for photosynthesis and other colors are only used for detection. However, depending on the detected environment the plant adapts itself to that.

What is P.A.R and the difference between P.A.R and lumens?

Lumens are the measurement for brightness observed by humans. As the human eye sees green light most prevalent, the measure lumen is weighed by the sensitivity of the human eye. We see green light best, meaning as more green light is in the spectrum, then higher is the lumen output from the light source.

To evaluate light sources for horticultural applications one can have two different ways of looking at light. One perspective is to look at light as a wave, then we are talking about P.A.R Watts. The other point of view is to have a look at light as particle (photon), then the measure is μmol/s, which means we are counting the photons.

If we are talking about P.A.R Watts, you have to know that the energy of a light wave depends on the wavelength. As shorter the wavelength as higher the energy from the light wave.P.P.F or P.A.R is not weighted with a sensitivity curve. That means a green photon has the same count as the red one.

Our internal research has shown that measuring photosynthetic active radiation is the most exact by measuring it in photons [μmol/s for PPF and μmol/m2/s for PPFD).

Can you break down what is meant by PPFD and why is that value important?

While P.P.F describes the total light output from a light source, the P.P.F.D describes the amount of light which arrives at a certain point on a certain target area. In easy words, P.P.F.D describes how many photos are raining on your plants.

How does LED lighting work compared to metal halide and H.P.S?

Metal halide and H.P.S lights are working with the physical principle of gas discharging. In the gas discharge, the luminous fluxes and mercury are excited by the current flow and release the excitation energy in the form of characteristic radiation. T

he mixture of radiation components of different elements, e.g. sodium vapor, gives the desired color spectrum.LED’s are working with the principle of a p.n. junction. Therefore, the combination of two different semiconductor materials determine the color and efficacy. This only stands for colored led. White LEDs are working with a blue led chip covered with a color conversation material, which generates white light (mixture of all colors) out of the blue excitation light.

As many different semiconductor materials can be combined almost every color can be achieved with led technology. Some “colored” LEDs are much more efficient than others. By soldering different color LEDs on a PCB almost every light spectrum can be realized.

Is there a bandwidth of light which plants use more than others?

Yes, blue and red light are absorbed best, while green light is partly reflected.

That means photosynthesis can be driven most efficient with red and blue light.After absorption the collected photon energy has to be transferred to the right energy level, which plants are using for photosynthesis. While blue photons have a high energy level which has to be transferred, the plant can use red photons without transferring. Thus, red light is most efficient.

What causes plants to stretch when they enter 12/12 and what can be done to keep them shorter at this time?

Stretching of plant is influenced by genetic, embedded sugar content and the plants environment. Light spectrum and intensity influences sugar production and is a main part of a plant’s environment. Thus, with light the stretch can be influenced dramatically.The easiest way to keep plants shorter is to increase the light intensity (P.P.F.D), in the stretching phase, in the opposite way less intensity will promote an increase in stretch once lights are changed to 12/12.

Could you explain more about red and far red spectrums?

With red and far red-light plants are detecting the presence of light. The ratio between this wavelength strongly influence morphology of plants. Far Red light (730nm) also helps to drive photosynthesis more efficient (Emerson effect). With use of only far red light at the end of the day growers can bring plants to flowering even if the light period is more than 12 hours.

Can you tell us more about your lab testing facilities?

Of course,…we are running three different plant labs. Two at our main facility (200m2) in Austria and one in Switzerland (100m2). In general, we are examining how different light spectrums and intensities influence plant development, drug content, yields etc. Each lab has few different chambers with same environmental conditions, but other lights. As the led technology is moving rapidly this research is done continuously and is a full time job.

What are the benefits of having passive cooled lights and what made you choose this design?

Active cooled grow lights are noisy, fragile and the fans are consuming energy. Especially in a large greenhouse environment fans are critical to work with. In comparison the passively cooled design is not wasting energy for powering up the fans. Although, the efficacy is better, as passive cooling doesn’t need moving parts it’s much more reliable. For that reason, all SANlight products are passively cooled. The design of Q-Series with many single light modules, helps to increase cooling efficacy. We can have a high cooling capacity with a very low amount of needed surface, in comparison to other lamps

Written and Published By Stoney Tark In Weed World Magazine Issue 141

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