PAR Light Quality LEDs & HID: Plant Grow Light Basics -101 (pt 1)

Hi, I’m Al Gracian from albopepper.


Today's grow light market is advancing fasterthan ever before, especially in the field of LEDs.

New models hit the market every month.

Lights become more efficient AND more affordable.

But the selection process is becoming morecomplex as well.

We must filter out over-inflated product claims.

Meanwhile, we're trying to understand thevarious product specs and what these mean for us.

What is PAR light? Do plants benefit from full spectrum lightor is red & blue all that they use? We'll answer this in this 1st video of a multi-partseries.

And then later, we'll get into PPF, PPFD andlight efficiency.

And finally we'll compare the pros and consof various light technologies and their form factors.

When looking at the characteristics of a lightsource, we can focus on two crucial aspects: First, there is Light Intensity which refersto how bright a light is.

This relates to the photon density.

(More on this in the next video.

) Secondly, there's Light Quality which is also important.

This refers to the composition of light.

How much red is emitted in relation to blues, greens or any other color? And that’s what we’re discussing today.

So lets start with the basics! Grow lights emit radiation within the visiblelight spectrum.

This chart, which you'll see time and again, portrays a narrow portion of the electromagnetic spectrum.

Each color has its own unique wavelength, from violet to red.

A specific color can be described by its wavelengthin nanometers (nm).

So a blue light may be 450 nm while greenis 550 and red is 680.

Travelling left on this graph, towards blue, each photon (or particle of light) has more and more energy.

Moving right, towards red, each light wavepossesses less energy.

As you get right outside of the visible spectrum(below 400 nm) you have Ultra-violet light.

Some grow lights may produce UV in additionto visible light.

And interestingly, plants have shown physiologicalresponses to UV with improved disease and pest resistance.

Between 710 and 850nm we have Far-red light, which plants are sensitive to as well.

Far-red does less to drive photosynthesis, but can greatly effect plant development or morphology.

For example, certain ratios of red to far-redcan tell plants that they’re under a canopy of taller plants, triggering them to growtaller in response.

Of course, the most crucial range for plantgrowth is within the 400 to 700nm color range.

Photons within this range are most effectiveat driving photosynthesis.

This is referred to as PAR light (PhotosyntheticallyActive Radiation).

Note that this range includes even green light.

Wait a second! Don't many growers emphasize blue and redfrequencies, saying plants don't use green light? They may refer to green as being completelywasted light.

Well, for decades researchers have demonstratedthat green light serves a useful function and is capable of driving photosynthesis.

In fact recent research is revealing someunexpected benefits of green light, even helping with organic pest control! The point is, don't prescribe to the oversimplifiedmentality that plants only need one or two colors to thrive.

They may live and grow, but that doesn't meanthat all other light frequencies are useless and unneeded.

But where did this misconception come from? Well one thing that doesn’t help is themisapplication of the photosynthesis absorption spectra.

People love bringing up this little graphwhich certainly makes green light APPEAR useless.

Even laying on that popular carotenoid graphstill leaves a big gap.

But how was this data gathered? This is based on testing of thin algal solutions.

Higher plants (you know the stuff that we’retrying to grow) do not respond to and process light in the same fashion.

They have much more complex structures.

In reality, “green leaves of land plantsabsorb a substantial fraction of green light.

” And this light then drives photosynthesisas well.

So yes, plant leaves reflect SOME green light.

And that’s why they’re green.

That’s good because this results in improvedcanopy penetration.

But ultimately, much of that light is ableto be harnessed.

Should that really surprise us though? Afterall, the PAR measurements used by horticulturistsgive green photons the same weight as blues and reds.

So really a broad, full spectrum light sourceis a good thing.

– not a bad thing.

A spectrometer can analyze a light sourcerevealing the ratios of one color compared to another.

Many light manufacturers will share spectralgraphs of their light.

It may be portrayed as a curve like this orperhaps this.

Plants respond differently to different combinationsor ratios of light.

At different phases of growth, certain spectrumprofiles may enhance results.

Professional growers may switch bulbs as theirplants mature and enter their fruiting or reproductive phase.

High Pressure Sodium lights are heavier inthe yellow through red end of the spectrum.

Meanwhile, Metal Halide lamps emit a largeramount of blue and UV.

You may be familiar with the Kelvin ratingsystem which is commonly used to describe the color characteristic of Fluorescent lights.

Lower numbers like 2100 K have a warm amberhue while "cooler bulbs" like 6500 K are higher in blue light.

With the widespread adoption of LEDs, we dosee LEDs that use a Kelvin rating – but many plant grow lights do not.

Instead, they may contain multiple diodes, each of which emits a unique narrow band of color.

A 3 band LED, for example, may contain 1 typeof blue and 2 types of red.

Thus, custom tuning of that "perfect" ratiois often sought ought as one LED seller tries to stand out from the rest.

LED Grow lights are showing more and morecolor bands.

Some even claim to be "full spectrum".

This can be achieved by including a few diodesthat have a phosphor coating.

The coating changes the energy state of photonsfrom a blue diode.

The result is a mixture of wavelengths thatproduce white light.

The reliance on phosphor coatings slightlyreduces an LED's efficiency rating.

But it creates a more rounded spectrum thatis likely to support a broad range of plant types.

Light Quality can have a drastic impact onplant development, effecting the shape and length of plant leaves.

But just as important is the overall LightIntensity.

What's the best way to measure light intensitywhen it comes to plants? Our next video will answer that question! Thanks for watching.

Please subscribe if you haven’t already.

And as always, Happy Gardening!.

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