How to know how much light is enough

[Bear777]

With dimmers and manufacturer's recommendations of things, how do you know how much is enough. For instance in veg I see recommendations of 50 to 100%. Is it just a matter of trial and error. Is there a usual time period, say after so many weeks that you should be using the lights near there max as long as your not seeing any heat damage, or is there no reason to use the lights near their max if say the plant is not in flower. Just trying to get a better understanding of what's going to be ideal, so I can learn from that. I figure the more I can find out about indoor, the easier the learning curve will be.

 

[Goonie Goat]

Depends on a load of different variables, like the type of light (I guess you are talking LED). Most pre-built lights will come with specs including PAR levels at different heights (even my $25 eBay led for my clones and seedlings had a guide on light intensity at different heights). Like you say most of these top end lights are way too bright even in flower so you either have to raise the light (and reduce the lifespan of your diodes, more voltage = more heat) or you dim the fixture and lower it which gives the same readings as the higher setting for less cost and less heat which should extend the life of the LED, but this is generally more suited to even canopies. Lux meters are not as accurate as par meters but it's a good tool to have to give an idea of brightness at certain distances, 5000-10000 or so for seedlings
15000-30000 for veg and upto 80000 for flower, although many things come into play such as strains and carbon dioxide etc etc. I got my lux meter cheap from eBay but they are only really good for white light but it takes some guesswork out

 

[Bullfrog]

unless you have a means of accurately measuring PAR then your fartin in the wind really.
Your going to have to trust the manufacturers numbers displayed on their PAR map/chart.
beyond that you learn to read your plants and make adjustments based on their behaviour.
a quantum sensor is pretty expensive but if yo have an iphone there is an app called photone that is surprisingly accurate. even still, following recommended PPFD levels is still a guide and varies depending on how ideal the other environmental factors are. so yes there is an element of trial and error but mostly your going to have to monitor and control as much as possible the main environmental factors like VPD , the NER and EC in your rootzone and air exchange ie CO2. They all work in harmony and you dial them in together.

 

[VinDeezle]

For an average led with an overall spectrum between 2700-3500k, you can multiply your lux by 0.0155 to get PAR within a few percent...depending on your spectrum it can be anywhere from 0.0148-0.017. CMH is the most efficient at turning luminous flux to active radiation at 0.017, whereas lights with heaps of stark blues a deep reds will need a different coefficient.

At the end of the day, as bullfrog mentioned,It all depends on the plants metabolism and several environmental factors as well. Personally I run everything at 35k lux (550umol/s) over 18 hours for veg and 950umol/s over 12 hours for flower which give a DLI of 30-40 for the whole grow as I have a pretty steady environment.

At the end of the day "percentage X at distance X" don't mean much. Lux meters are cheap and convert to PAR easily, but the plants body language will do most of the heavy lifting.

 

[One Drop]

Light metre is a variable tool to have to get that sorted mate

 

[VinDeezle]

When it comes to "how much is enough", that's definitely strain and environment dependant.

I'll usually find the girls will let me know if accumulation is getting out of hand as they will "go to sleep" well before lights out. Will start to noticeably posture down once it hits an adequate DLI.

Tbh, I found I was always running way too much accumulation of light before investing in a lux Meter and quantifying my DLI. the added bonus is a that I basically dimmed all my lights considerably, saving heat and power at the same time

 

[turbo]

All of this stuff seems far too technical for the average modern day lazy joe.

I've relied on a free to download app called "Photone" to get my light right and it has been a piece of piss being entirely new to growing anything in general with one run under the belt. I gauge plant light intake happiness by whether or not they pray diagonally upwards and whether or not the leaves show signs of "tacoing".

Though I am still pondering whether or not it's worthwhile to run my light at higher wattage raised up for penetration or keep it close at lower wattage and save money.

 

[frankreynolds]

How much light is too much.... How much c02 you giving those plants?

In all seriousness Lux is a very very generalized reading so I would be careful as it measures light that humans can see, not light that plants can use (that would be an ePar meter)

Different lights will give off different footprints. For eg. Bar style LED versus a more concentrated LED pattern like boards. To get similar canopy PAR levels will require different hanging heights even if both lights are run at the same power level.

So in the end if you don't have fancy meters I would be following companies directions.

 

[VinDeezle]

How much light is too much.... How much c02 you giving those plants?

In all seriousness Lux is a very very generalized reading so I would be careful as it measures light that humans can see, not light that plants can use (that would be an ePar meter)

Different lights will give off different footprints. For eg. Bar style LED versus a more concentrated LED pattern like boards. To get similar canopy PAR levels will require different hanging heights even if both lights are run at the same power level.

So in the end if you don't have fancy meters I would be following companies directions.

At the end of the day, lux meters measure very similar spectrum of light as a PAR meters do, and only requires a basic conversion to convert between them with decent accuracy. Lux meters run light through three cones, one 400-500nm, one 450-630nm and one 600-700nm which is very similar to Active PAR range. You'll find the conversions are off by a few percent max depending on how much stark blue and far red your board has. Takes a few seconds to multiply or divide one number by another.

We have to do lux conversions to PAR when setting light for culture medium sampling and its accurate enough. I borrow a par meter from a mate when I get a new light and figure out the coefficient at which it converts luminous flux to active flux. Takes a few seconds, and from then on all i need is a cheap lux meter. Just divide the par reading by the lux reading and it will give you the coefficient for the rate of conversion. Eg 730umols/s divided by 48500 makes 0.1505.

My boards with a 3000k overall spectrum convert Luminous flux to PAR the most efficiently at a coefficient close to 0.016, whereas the same lights on seedling spectrum produce more visible light, less active radiation and convert at a rate of 0.0148.

 

[Bullfrog]

All of this stuff seems far too technical for the average modern day lazy joe.

I've relied on a free to download app called "Photone" to get my light right and it has been a piece of piss being entirely new to growing anything in general with one run under the belt. I gauge plant light intake happiness by whether or not they pray diagonally upwards and whether or not the leaves show signs of "tacoing".

Though I am still pondering whether or not it's worthwhile to run my light at higher wattage raised up for penetration or keep it close at lower wattage and save money.

saving money costs you money. the yield is directly proportionate to the amount of watts you pay for. assuming your not wasting anything. maximising photosynthesis i guess is the answer to that. If im growing a pound of flower I honestly couldnt give a screaming fuck about an extra $20 on the power bill

 

[turbo]

saving money costs you money. the yield is directly proportionate to the amount of watts you pay for. assuming your not wasting anything. maximising photosynthesis i guess is the answer to that. If im growing a pound of flower I honestly couldnt give a screaming fuck about an extra $20 on the power bill

So you're saying 1000ppfd up close with light running 30% will yield less than 1000ppfd from far away running at 90%?

 

[veritas629]

A PAR meter is very useful, but an expensive investment for a new grower. It's good to learn how to do things by eye, because sometimes sensor numbers aren't the whole story. Start with the manufacturer's recommendations and do some research. If you get a well known light and are using it in a standard size tent, somebody on TSE will likely have some experience to share.

My advice, start at a lower power and work your way up to the manufacturer's recommendations. Too little light rarely hurts anything but yield and adds some extra stretch. I find that too much light makes for crispy buds, less flavour & aroma, occasionally nutrient issues, excess heat to deal with, and bigger electricity bills. Also, don't nuke your sprouts or seedlings, the young plants can't handle the high power a flowering plant can.

 

[Bullfrog]

So you're saying 1000ppfd up close with light running 30% will yield less than 1000ppfd from far away running at 90%?

1000umol is 1000umol no matter how you arrive at it. what you will alter with different hanging heights is how evenly the photons are distributed over the canopy. their will be a variable attributed to reflection off the walls too. you would have to measure directly under the light fixture and at the borders to find the sweet spot. or trust the manufacturers recommendations but a lot of the time manufacturers dont provide very many test heights they just wanna flash their big numbers around.
Its hard to give a one rule fits all because their is so many different light fixtures but "generally" Ive found around 600mm is a nice balance point for efficiency. depending on the light you might have to stay a bit further away for seedlings and of course in flower the smaller wattage lights like the 200-300W fixtures can come half that distance closer again without problem.

 

[Bullfrog]

1000umol is 1000umol no matter how you arrive at it. what you will alter with different hanging heights is how evenly the photons are distributed over the canopy. their will be a variable attributed to reflection off the walls too. you would have to measure directly under the light fixture and at the borders to find the sweet spot. or trust the manufacturers recommendations but a lot of the time manufacturers dont provide very many test heights they just wanna flash their big numbers around.
Its hard to give a one rule fits all because their is so many different light fixtures but "generally" Ive found around 600mm is a nice balance point for efficiency. depending on the light you might have to stay a bit further away for seedlings and of course in flower the smaller wattage lights like the 200-300W fixtures can come half that distance closer again without problem.

I probably confused the issue a bit there. You are correct in saying that reducing the height will give you a target ppfd at a lower energy consumption. That is true probably only if your too far away and just wasting energy. There is mathematically an ideal height for achieving the best light coverage for your canopy and thats what is going to give you the best result and yield. Once you move away from that your trading cost for yield.

 

[afghan bob]

There u go 777
Yup ure question is answered
To bad u need diploma of science to understand what it means

 

[Goonie Goat]

There u go 777
Yup ure question is answered
To bad u need diploma of science to understand what it means

Hahaha I was gonna say the poor blokes head has probably exploded trying to put all of this together

 

[Bullfrog]

this should fuckin clear it up for ya

 

[frankreynolds]

At the end of the day, lux meters measure very similar spectrum of light as a PAR meters do, and only requires a basic conversion to convert between them with decent accuracy. Lux meters run light through three cones, one 400-500nm, one 450-630nm and one 600-700nm which is very similar to Active PAR range. You'll find the conversions are off by a few percent max depending on how much stark blue and far red your board has. Takes a few seconds to multiply or divide one number by another.

We have to do lux conversions to PAR when setting light for culture medium sampling and its accurate enough. I borrow a par meter from a mate when I get a new light and figure out the coefficient at which it converts luminous flux to active flux. Takes a few seconds, and from then on all i need is a cheap lux meter. Just divide the par reading by the lux reading and it will give you the coefficient for the rate of conversion. Eg 730umols/s divided by 48500 makes 0.1505.

My boards with a 3000k overall spectrum convert Luminous flux to PAR the most efficiently at a coefficient close to 0.016, whereas the same lights on seedling spectrum produce more visible light, less active radiation and convert at a rate of 0.0148.

Similar but not the same, the LED i have from growlightsaustralia will show 10% less on a par meter compared to the new ePar meter which takes on an even larger spectrum due to the added UV and far red. lux even less, might be good enough not for me personally.

So you're saying 1000ppfd up close with light running 30% will yield less than 1000ppfd from far away running at 90%?

That 1000ppfd close up at 30% will also be throwing much less light below that single plane of 1000ppfd due to square inverse law or whatever its called. There is a reason commercial growers hang lights high up at high watts. to evenly light up a room.

 

[Bear777]

Wow, that's a lot of info to take in, but that is truly what I wanted, the ins and outs of how much light to use beyond just a general manufacturer recommendation. This forum is great, I'm learning heaps. My wife has an iPhone so I'll download that app too. I only have sf4000 spider farmer at the moment, so if anyone has any recomendations when using that light, I will take that on board as well. I am saving up for a HLG though.

 

[Bear777]

unless you have a means of accurately measuring PAR then your fartin in the wind really.
Your going to have to trust the manufacturers numbers displayed on their PAR map/chart.
beyond that you learn to read your plants and make adjustments based on their behaviour.
a quantum sensor is pretty expensive but if yo have an iphone there is an app called photone that is surprisingly accurate. even still, following recommended PPFD levels is still a guide and varies depending on how ideal the other environmental factors are. so yes there is an element of trial and error but mostly your going to have to monitor and control as much as possible the main environmental factors like VPD , the NER and EC in your rootzone and air exchange ie CO2. They all work in harmony and you dial them in together.

Those abbreviations VPD, NER, EC, what do they stand for, if I would guess maybe ventilation pressure differential? as I see it mentioned when talking about humidity, NER no idea, and EC I thought maybe I read somewhere it had to do with electrical conductivity but I really don't know....but I better find out if they're some of the main environmental factors, so many abbreviations now a days used in different circles.