Understanding light.

[BigCube]

Just a short disclaimer here, I am not an expert. I've done my own research, I will show my sources and I am willing to be corrected.
I will try my hardest to keep my bias out of the equation as best I can.

Light a small portion of the electromagnetic radiation spectrum:

<img>https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_compare_level1_lg.jpg</img>

 

[BigCube]

Just a short disclaimer here, I am not an expert. I've done my own research, I will show my sources and I am willing to be corrected.
I will try my hardest to keep my bias out of the equation as best I can.

Light a small portion of the electromagnetic radiation spectrum:

https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_compare_level1_lg.jpg

Within this narrow band of the spectrum is the visable light spectrum.

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 380 to 740 nanometers.

Visible spectrum - Wikipedia

en.wikipedia.org

This is what we are primarily interested in when growing plants. And what we are measuring when we measure Lumens.
There is a tiny bit leading in to and out of the spectrum that plants can use we know as ultraviolet and far red.

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time.

Lumen (unit) - Wikipedia

en.wikipedia.org

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

Photosynthetically active radiation - Wikipedia

en.wikipedia.org

So, you might be asking: What's the deal? Both those spectrum's are almost exactly the same. What's actually being measured, and how can we use this information to help us grow plants?

Well in short, they are both measuring the same thing different ways. One is slightly more accurate when dealing with plants.

PAR Is a measure of the actual radiation hitting the sensor, the sensor being a known size, some math is done and you are given a number representing the actual amount of Photosynthetically active radiation. It is relative to a standard formula and thus you have a standard unit of measure.

Lumen is a measure of the visible light spectrum as compared to 1 Candela (Candle).
Lumens are Slightly weighted to the human eye, so it gives more weight to brighter colors.

So you can see, they are both valid unit of measuring light for both humans, and plants. Since they are both measuring the same part of the spectrum, the numbers can be interpreted to denote more or less light on a scale. Par will be a little more accurate as is it measuring the actual radiation hitting the surface and lumens is measuring the amount of visible light of an area.

Higher Lumen counts must equal higher PAR values and vice versa. since they are measuring the same thing, and more is more. Keep that in mind if you've been talking yourself in to buying a costly PAR meter. The only real reason to own a PAR meter, is so you will have accurate PAR measurements. But if more par = more lumens and more lumen = more par. you're just paying for a name. Conversely there are formulas that can give you accurate PAR number from Lumens. Even online calculators that do it for you.

Convert Lumens to PPF - Online Calculator | Waveform Lighting

Online calculator to convert luminous flux (lumens) to PPF (micromoles per second).

www.waveformlighting.com

 

[Mr.jiujitsu]

Just a short disclaimer here, I am not an expert. I've done my own research, I will show my sources and I am willing to be corrected.
I will try my hardest to keep my bias out of the equation as best I can.

Light a small portion of the electromagnetic radiation spectrum:

View attachment 924727
https://imagine.gsfc.nasa.gov/Images/science/EM_spectrum_compare_level1_lg.jpg

Within this narrow band of the spectrum is the visable light spectrum.

View attachment 924728

The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 380 to 740 nanometers.

Visible spectrum - Wikipedia

en.wikipedia.org

This is what we are primarily interested in when growing plants. And what we are measuring when we measure Lumens.
There is a tiny bit leading in to and out of the spectrum that plants can use we know as ultraviolet and far red.

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time.

Lumen (unit) - Wikipedia

en.wikipedia.org

Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

Photosynthetically active radiation - Wikipedia

en.wikipedia.org

So, you might be asking: What's the deal? Both those spectrum's are almost exactly the same. What's actually being measured, and how can we use this information to help us grow plants?

Well in short, they are both measuring the same thing different ways. One is slightly more accurate when dealing with plants.

PAR Is a measure of the actual radiation hitting the sensor, the sensor being a known size, some math is done and you are given a number representing the actual amount of Photosynthetically active radiation. It is relative to a standard formula and thus you have a standard unit of measure.

Lumen is a measure of the visible light spectrum as compared to 1 Candela (Candle).
Lumens are Slightly weighted to the human eye, so it gives more weight to brighter colors.

So you can see, they are both valid unit of measuring light for both humans, and plants. Since they are both measuring the same part of the spectrum, the numbers can be interpreted to denote more or less light on a scale. Par will be a little more accurate as is it measuring the actual radiation hitting the surface and lumens is measuring the amount of visible light of an area.

Higher Lumen counts must equal higher PAR values and vice versa. since they are measuring the same thing, and more is more. Keep that in mind if you've been talking yourself in to buying a costly PAR meter. The only real reason to own a PAR meter, is so you will have accurate PAR measurements. But if more par = more lumens and more lumen = more par. you're just paying for a name. Conversely there are formulas that can give you accurate PAR number from Lumens. Even online calculators that do it for you.

Convert Lumens to PPF - Online Calculator | Waveform Lighting

Online calculator to convert luminous flux (lumens) to PPF (micromoles per second).

www.waveformlighting.com

Excellent information

 

[BigCube]

Now that you understand the numbers, what they mean and how to use them. Lets look a bit closer at the light itself.

Most people don't need to be told that white light is made of all the colors in the visual spectrum. what may not be obvious to some people is that "white" light has quite the range usually expressed in a temperature (kelvin ) Normally ranging from around 2500k to 6500k. What this relates to visually is a warmer or brighter light Caused by more red or blue in the spectrum.

It's not as simple as this, but in general. Plants like to have more blue in Veg, this causes them to stretch up and out and gain height and width. Generally promotes farther node spacing and less foliage growth. In Flower they prefer a more red spectrum. This causes them to bush up, get tight node spacing and grow more foliage.
For these reasons some growers use a Bluer spectrum (5000k to 6500k) in veg and a red-er spectrum in flower (2700k to 3500k). But equivalent results can be had by both flowering and vegging under the same light. In some cases, people go right in the middle with 4000k and have great results.

Personally I prefer 2700k to 3000k cause veg isn't as long as flower and I like bushier plants with shorter node spacing.

Green yellow and orange also play their part. It differs from plant to plant, but things like leaf thickness, flavor and leaf color are some of the factors the other spectrum's can affect. I am far from a scientist, and am just begining to grasp this aspect of lighting, as are most scientists. A good introduction to it can be found here:

 

[BigCube]

Ok, now we know what we want out of a light. How much of it do you need?

Well there is no real hard and fast rule, we can look at some of the requirements of our environment.
Mainly the size. Larger areas obviously require more light. But how much?
Well the general consensus is:

LED:
30w - 45w per square foot. ( I like a minimum of 35w/sq)

HID:
60w - 80w per square foot.

From there you can raise and lower your lights as needed.

Now lets talk about Lux, as this usually ends up being the easiest cheapest way to measure light.
The lux (symbol: lx) is the SI derived unit of illuminance, measuring luminous flux per unit area.[1][2] It is equal to one lumen per square metre.

Lux - Wikipedia

en.wikipedia.org

Lux is just another way of measuring Lumens, so we are still talking about the same light here. you can download free apps for your phone that allow you to measure lux, you can then convert them to lumens and par if you wish. But it's just another standard of measuring the same thing.
So here are some of the more common lux values you are looking for:

Seedling/cuttings: 2000-3000 lux
Mother plant/mild veg: 10000 - 15000 lux
Aggressive Veg and flower: 45000 - 80000 lux (strain and environment dependent) A safe number to aim for is 55000 lux and play with it from there, via raising and lowering your light.

These are round about numbers, but have worked well for me.

Next thing to consider is the light distribution. It is much more beneficial to have your light distributed evenly across your footprint. This prevents hot and cold spots in regard to both temperature and light. Using COBS or HID lights, that emit light from a single source often create "hotspots" that cause your canopy to grow unevenly. Parts of the plant directly under the light grow faster and taller than the rest of the plant, this only compounds the problem cause it then shades the parts of the plant below it even more. While it is a viable option for lighting, it is not optimal. Fixtures like the quantum board have a much better distribution of light, enabling you to keep a much more even canopy and ensuring your plant is getting the same amount of light over its entire surface.

 

[SkunkyDunk]

Could you elaborate on the 30w to 45w led to 60w to 80w HID.
Is it because the HID has a hot spot (less efficient)and the led is spread out (more efficent)?

 

[Aqua Man]

Could you elaborate on the 30w to 45w led to 60w to 80w HID.
Is it because the HID has a hot spot (less efficient)and the led is spread out (more efficent)?

It's not the spread it's just the efficiency difference. In other words LED puts out more ppfd per watt than HID lighting.

 

[Aqua Man]

Great work @BigCube

 

[BigCube]

Could you elaborate on the 30w to 45w led to 60w to 80w HID.
Is it because the HID has a hot spot (less efficient)and the led is spread out (more efficent)?

@Aqua Man is correct. It's just the efficiency difference.

Good reflectors on HID lights can spread the light pretty even, but they do always have that hotspot in the middle still.

 

[Sungoddes1]

I've got all that, I'm trying to figure out what my ppfd should be for my space? I have pages of calculations for watts to lumens, for lumens per sq ft, for my PAR. I know I have 630.34 umol/s in a 10×12×10 space. I'm brain locked from the math, maybe im not looking in thet right place to find my answer. Can someone help, am I running enough light?

 

[Buzzer777]

Lumens are not an accurate way to measure LEDs. Like you have 120 sq ft of space. Using 50 watts per sq ft, you will need 600watts of white lights (TRUE watts)
I run a bit over 70 watts per sq ft myself, and use dimmers when appropriate.

 

[Sungoddes1]

Lumens are not an accurate way to measure LEDs. Like you have 120 sq ft of space. Using 50 watts per sq ft, you will need 600watts of white lights (TRUE watts)
I run a bit over 70 watts per sq ft myself, and use dimmers when appropriate.

Yes after much research I found that out. So my LEDs are 35w, my blue and red spectrum are a little above required. I don't have any extra white light running. I have 2 plants under each light, 2 lights. Everything is ok, and that's the problem it's just ok. I just need a number then I can market the rest happen.

 

[Buzzer777]

Yes after much research I found that out. So my LEDs are 35w, my blue and red spectrum are a little above required. I don't have any extra white light running. I have 2 plants under each light, 2 lights. Everything is ok, and that's the problem it's just ok. I just need a number then I can market the rest happen.

I would say that you will need at least 600 watts of white, and maybe 800watts in flower with Burples. Your present 35 watt lights (what are they?) will not get you anything in flower. It will be easier to help if you can provide more details?

 

[weedtech]

Indeed - the ways we measure light have changed. Please take a look at this - Know your light sources

 

[BigCube]

Yes after much research I found that out. So my LEDs are 35w, my blue and red spectrum are a little above required. I don't have any extra white light running. I have 2 plants under each light, 2 lights. Everything is ok, and that's the problem it's just ok. I just need a number then I can market the rest happen.

You need 35w per square foot of grow space. Not per plant. If you're in a 2x4..
2 x 4 = 8 x 35 = 280. You need a minimum of 280w of led light.

3x3=9x35=315w
4x4=16x35=560w

Minimum. You will find the numbers quite respectable.

 

[BigCube]

I've got all that, I'm trying to figure out what my ppfd should be for my space? I have pages of calculations for watts to lumens, for lumens per sq ft, for my PAR. I know I have 630.34 umol/s in a 10×12×10 space. I'm brain locked from the math, maybe im not looking in thet right place to find my answer. Can someone help, am I running enough light?

10x12=120x35=4200w minimum for a 10x12 footprint.

If you're set on using ppfd or par as a measurement, you will need to buy their fancy expensive meters to get any real accuracy.

Use the par calculator I posted a link to above to give you numbers that will be fairly close.

The real question is, why are you using unimol or par as a standard when you have no way to measure them yourself?
Just because someone else uses them doesnt mean you have to. Specially when the other units of measure work just fine.

Look at it like you're trying to convert the gas milage of your car to grams per hour.
Sure it will be a more accurate measurement of how many grams of fule per hour it's going to burn. But Miles per gallon end up being good enough to estimate your fule consumption. They both work, one is slightly more accurate but not worth the trouble to measure and calculate. Other units of measure can be used to determine the same information within a very small deviation not even worth paying attention to.

Unless you're a scientist, paying with formulas and testing environmental factors and how they relate to light, in a setting where you need absolute accurate ppfd numbers you then would document and use in mathematical formulas, you dont need to measure in ppfd or par.
You can, but it's a lot of money and trouble for zero gain. When you can simply use another unit of measure.

 

[BigCube]

The entire point of this post was:

People put too much importance in PAR and ppfd numbers. I guess cause that's what science uses to measure it in horticulture lighting.

The reality is, light it light. Measure it however you will, it doesnt change the light at all. Pick a unit of measure that you can easily and cheaply measure and use that.

They are all measuring the same thing different ways. Why care how many grams per minute your car consumes in gas when miles per gallon will do?

If you want to play scientist, and have the fancy numbers for what.... just to know I guess.. then sure blow your money on expensive testing equipment or long periods of time trying to convert what you can measure to the flashy fancy look at me numbers.

But it's not needed. You don't need to measure your fule consumption with un burnt hydrocarbon molecules per second to know how how far the car will go on a specific amount of fuel. You can measure it, and find the number. But why even care when mpg works?

Conversely, you dont need to measure how many moles you have in a specific space, when lux or lumens will do.

I'm tired of laboring the same point over and over. People arent measuring their nutrients or water in moles... litres, gallons and ml are fine.

You sure can measure your nutrients in moles. And sure it will be more accurate. But it's silly to think you must use moles to measure them to have any real results.

Specially when you dont have any way to measure it or even understand what it means. Higher numbers = more in every one of these scales. That's all you need.

 

[Rootbound]

You need 35w per square foot of grow space. Not per plant. If you're in a 2x4..
2 x 4 = 8 x 35 = 280. You need a minimum of 280w of led light.

3x3=9x35=315w
4x4=16x35=560w

Minimum. You will find the numbers quite respectable.

For me, 35watts per square ft would be the high end with my HLG quantum boards. I normally run 25-30 watts per square ft in flower and a little less in veg with very good results. I could prob turn them up some if I was maybe using co2.

 

[Farmer P]

Now that you understand the numbers, what they mean and how to use them. Lets look a bit closer at the light itself.

View attachment 924729

Most people don't need to be told that white light is made of all the colors in the visual spectrum. what may not be obvious to some people is that "white" light has quite the range usually expressed in a temperature (kelvin ) Normally ranging from around 2500k to 6500k. What this relates to visually is a warmer or brighter light Caused by more red or blue in the spectrum.

It's not as simple as this, but in general. Plants like to have more blue in Veg, this causes them to stretch up and out and gain height and width. Generally promotes farther node spacing and less foliage growth. In Flower they prefer a more red spectrum. This causes them to bush up, get tight node spacing and grow more foliage.
For these reasons some growers use a Bluer spectrum (5000k to 6500k) in veg and a red-er spectrum in flower (2700k to 3500k). But equivalent results can be had by both flowering and vegging under the same light. In some cases, people go right in the middle with 4000k and have great results.

Personally I prefer 2700k to 3000k cause veg isn't as long as flower and I like bushier plants with shorter node spacing.

Green yellow and orange also play their part. It differs from plant to plant, but things like leaf thickness, flavor and leaf color are some of the factors the other spectrum's can affect. I am far from a scientist, and am just begining to grasp this aspect of lighting, as are most scientists. A good introduction to it can be found here:

In the first minute of the vid he is speculating about why people thought that plants don't use green light (his attitude seems to be that it is because they are dumb) and totally missing the obvious. THE PLANT APEARS TO BE GREEN BECAUSE IT IS REFLECTING ALMOST ALL OF THE GREEN LIGHT!!!! When you look at something, actually anything, it appears to be a certain color because it is absorbing all of the colors except the one which you see. This is a very basic concept and does not need to be made confusing with long arguements. I use a green headlight all the time in my garden because the light is off when I am awake and vice versa. I have not gotten re-veg or even nanners because of it. In fact my only experience with nanners has been on feminized plants, though I know it can happen with regular seeds. With regular seeds it is usually because of bad breeding or someone flowers it too long and the survival of the species gene kicks in.
Sorry for the rant, now back to your regularly scheduled programming lol.

 

[MIMedGrower]

In the first minute of the vid he is speculating about why people thought that plants don't use green light (his attitude seems to be that it is because they are dumb) and totally missing the obvious. THE PLANT APEARS TO BE GREEN BECAUSE IT IS REFLECTING ALMOST ALL OF THE GREEN LIGHT!!!! When you look at something, actually anything, it appears to be a certain color because it is absorbing all of the colors except the one which you see. This is a very basic concept and does not need to be made confusing with long arguements. I use a green headlight all the time in my garden because the light is off when I am awake and vice versa. I have not gotten re-veg or even nanners because of it. In fact my only experience with nanners has been on feminized plants, though I know it can happen with regular seeds. With regular seeds it is usually because of bad breeding or someone flowers it too long and the survival of the species gene kicks in.
Sorry for the rant, now back to your regularly scheduled programming lol.

They have proven that plants use plenty of green spectrum. It penetrates deeper into the canopy. And it sparks photosynthesis like all the other usable light. I think the reflecting off of the leaves is how it penetrates dense foliage. Only some is reflected.

Plus leaves are not solid. They are more of a screen or membrane to light. Some is absorbed and some reflected from all color spectrum.