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Light Intensity

Light Intensity

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Plant Science Topics:

 

-Plant growth curve in response to increasing light intensity

-Light saturation point

-Rooting cuttings

-PAR light

-Difference between intensity (PPFD) and total light delivered (DLI)

-Gear for measuring light intensity

 

Recommendations to Apply the Science:

 

-Proximity to crop

-Situations that call for high intensity

-Situations that call for low intensity

-Lights with ability to adjust intensity

-How to maximize light with reflective surfaces

 

Product References:

 

-Black White Poly

-Quantum PAR Meter

-VGS Grow Rack Big

-oxyCLONE 80 Site Cloning System

-oxyCLONE 40 Site Cloning System

-Phantom DE

-Autopilot PX1

-Jump Start T5 48W 4’ LED Strip/Reflector Fixture

-Jump Start 24W 2’ LED Strip/Reflector Fixture

-Solar System 1100

-Solar System Controller

 

 

Welcome to Episode 9, we’ve reached the third and final fundamental of horticultural lighting. We covered light duration, light quality, and now light intensity.

 

Light quantity, or light intensity can be measured in several ways, but generally in horticulture we are measuring light that falls within a specific range or 400-700 nm. This is the PAR range, or photosynthetically active radiation. In episodes 3 to 8 we covered light that falls outside that range including UV, far-red, and infrared, but for light intensity measurements we’ll only be using the PAR range of 400-700 nm.

 

Light in the PAR range can be measured instantaneous in PPFD, photosynthetic photon flux density. The units are umol per m2 per second. Imagine this as a single blast from a hose, how much water comes out in one second. Light in the PAR range can also be measured cumulatively in mols per m2 per day, this is referred to as the DLI or Daily Light Integral. Imagine this as the total amount of water coming from that hose in a day.

 

(long slow blast of water and quick mega blast of water) The total amount of light in a day, or DLI, can be delivered in many ways. A low PPFD could be delivered on a 24 hour photoperiod or a light that puts out 24 times the amount of light could be run for just 1 hour a day, and both would create the same DLI. Obviously there is a balance that can be found by using a reasonable PPFD, instantaneous intensity, for a reasonable photoperiod or duration.

 

Plants max out on how much light they can absorb, giving a lot at once will not be effective, they will have already reached their ‘saturation point’ and the excess light will be wasted. But delivering low light for a long photoperiod isn’t always an option either as many plants are sensitive to photoperiod, like we saw with the short day plants in episode 2.

(Plant growth curve in response to increasing light intensity. Light saturation point)

 

It is common for new growers to give too little or too much light. Too little will result in leggy growth. Too much can be wasteful or damage crops. A light meter is a great investment if possible, many crops have recommended DLIs that have been recommended by universities. Here are some very rough general recommendations, but each situation is different depending on environment, crop, crop maturity, and a slew of other factors, so just take these as rough recommendations.

 

Alright, let’s take a look around the farm to see how I practically use various light intensities…

 

clones/cuttings. Seen benefits from some time off, I like 18 or 20 hours, but is benefit of stable temperature when 24 hours on.

 

Greenhouse (shot at night)

Difficulty of calculating (location, season, greenhouse structure)

Some lights can be controlled by meters that measure natural light intensity and adjust the intensity of the grow lights to reach target levels set by the grower

Calculating light in greenhouse video

New method of using led in summer

Led during summer with shade cloth

Uses all three of the fundamentals

Let’s start with intensity, too strong at once. So we are adding shade

But to reach a daily target level, we extend photoperiod

Quality. Blues in spectrum can help create compact growth, in warm conditions like a greenhouse in the summer, some plants tend to stretch in response to the heat, blue can help keep them more compact. And LEDs create virtually no infrared so there is less heat build up in the leaves, and LEDs are efficient so they create less heat in general in the greenhouse.

 

Indoors

Light intensity is very dependent on positioning

This is important in a greenhouse too, but indoors there are generally more restrictions on positioning. If growing in a rack like this, the light should be selected for that purpose… too powerful bad idea. In a tent, it is nice to have ability to adjust intensity, or select a light sized appropriated for tent.

 

Couple extra factors on light intensity. Many lightbulbs have use recommendations, as they eventually have reduced output and should be replaced. Some hoods have protective covers, these can reduce light intensity sometimes, especially if they get dusty. And light intensity can be improved by adding reflective surfaces in the grow room.

 

This has been Episode 9 of Plants and Light. For more information visit FarmerTyler.com. In the next episode we look at the interaction of the three fundamentals of horticultural lighting and how they should all be considered when choosing a grow light. I’m Farmer Tyler, and the more you know the better you grow.

 

Product References:

 

-Black White Poly

-Quantum PAR Meter

-VGS Grow Rack Big

-oxyCLONE 80 Site Cloning System

-oxyCLONE 40 Site Cloning System

-Phantom DE

-Autopilot PX1

-Jump Start T5 48W 4’ LED Strip/Reflector Fixture

-Jump Start 24W 2’ LED Strip/Reflector Fixture

-Solar System 1100

-Solar System Controller



 

before we  looked at two ways. Instantaneous intensity and cumulative. Instantaneous would be how many photons of light are being emitted per second, cumulative would be how many total photons of light are delivered over a day. A simple anology is the flow rate of a hose.

 

The amount of water coming out of this hose each second, or the gallons per second, would be similar to the instantenous light output measurement of a grow light. (look at bucket) the total amount of water that comes out in a day, or gallons per day, is similar to the cumulative light output measurement of a grow light.

 

Let’s go through some of the terms, first PAR or photosynthetically active radiation. This is the range of light that can be used for photosynthesis, it ranges from 400 to 700 nm.