Lux and height

Good morning folks.

Gonna start with this disclaimer. I'm new to tent growing. Asking questions to get a better understanding.

When it comes to height of my light vs FC or lux.

Say my light is supposed to be 30 inches away which would give a 150 fc or 15000 lux. Now say I have it 15 inches away but dimmed to 50% and the lux is 15000 does the distance actually matter anymore if the lux is correct?

I understand to close can ruin a footprint. That I get. But what if its not too close to ruin a footprint?

Again I'm new to grow lights. I have only grown outdoors.

Thanks,
Wiz

Wizzlebiz said:

Good morning folks.

Gonna start with this disclaimer. I'm new to tent growing. Asking questions to get a better understanding.

When it comes to height of my light vs FC or lux.

Say my light is supposed to be 30 inches away which would give a 150 fc or 15000 lux. Now say I have it 15 inches away but dimmed to 50% and the lux is 15000 does the distance actually matter anymore if the lux is correct?

I understand to close can ruin a footprint. That I get. But what if its not too close to ruin a footprint?

Again I'm new to grow lights. I have only grown outdoors.

Thanks,
Wiz

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Haven't tried to sit the light closer, but I have heard the weaker the intensity the closer it should be.
I kept my seedlings under 4x 6500k cfl til 3 sets of leaves grew out. Then I put the sf1000 at 24 inches 40% power.
With better led I wouldn't keep it too close to the babies. Not sure about the lux or anything like that. Only what I've done, and how it turned it out.

I find seedlings early veg enjoy 20-30k lux while flowers enjoy 50k+

my Samsung might not be super accurate but its a lux meter app and it is telling me that 3ft from my 600w hps is 24k lux so sounds somewhat accurate

this guy is great his videos are based on science and he is also the creator of a light sensor company

I've been looking at some charts on lux, fc, and par.

The general consensus of what I have read has been this.

A lux meter app is accurate btw. I tried 3 and my buddies actual lux meter and he was a bit perturbed at how accurate it was. Lol.

Wizzlebiz said:

I've been looking at some charts on lux, fc, and par.

The general consensus of what I have read has been this.
View attachment 4747364
A lux meter app is accurate btw. I tried 3 and my buddies actual lux meter and he was a bit perturbed at how accurate it was. Lol.

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good I'm glad they are somewhat accurate

kovidkough said:

this guy is great his videos are based on science and he is also the creator of a light sensor company

Click to expand...

Just watched this. And yea that makes tons of sense. Luckily we have technology in out phones that see all the spectrums including blue and red equally.

They do have external adapters for the phone for quantum readers if you wanna get truly precise though.

Due to an equipment failure back when I was growing indoors I had to use an underpowered LED panel for one of my plants. I just put it closer to the canopy and the plant did just fine.

My question because I’m new is what indicators show height is good? and what’s shows the height is too low or too high?

Crackiller said:

My question because I’m new is what indicators show height is good? and what’s shows the height is too low or too high?

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the space between nodes will stretch , meaning the plant is trying to almost reach acceptable light levels

too low can lead to light burn. similar to sun burn on our skin

Well, if you want my data...

I just stood under a normal ceiling light.

Galaxy 20 using Lux Light Meter = 210 lux
Hanna HI 97500 = 153lux

At 5000lux on the Hanna, LuxLightMeter was >= 500lux over.

Wizzlebiz said:

Say my light is supposed to be 30 inches away which would give a 150 fc or 15000 lux. Now say I have it 15 inches away but dimmed to 50% and the lux is 15000 does the distance actually matter anymore if the lux is correct?

I understand to close can ruin a footprint. That I get. But what if its not too close to ruin a footprint?

Click to expand...

In this specific comparison, your footprint will be half the size, but your basically getting the same amount of light in that footprint. Personally i would just keep it at 30'' and 100% unless your having heat issues but it sounds like you are running a pretty small light. Your electric costs are probably 1-2 cents per hour at 100%

JoeBlow5823 said:

In this specific comparison, your footprint will be half the size, but your basically getting the same amount of light in that footprint. Personally i would just keep it at 30'' and 100% unless your having heat issues but it sounds like you are running a pretty small light. Your electric costs are probably 1-2 cents per hour at 100%

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It was honestly not about energy consumption and more about using the dimmer to control intensity instead of moving the light which would just be easier.

Wizzlebiz said:

It was honestly not about energy consumption and more about using the dimmer to control intensity instead of moving the light which would just be easier.

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Youll find you dont have to move the light much. Set it at 30'' and let the plant "grow into it". Then by the time you are that big, your light needs to be at 100% anyway.

Hi everyone,

Don't want to open a new thread, this problem is very similar to mine. I have changed my HPS bulb recently, it is 250W and 32.000lumen. I have 60x60cm (2ftx2ft) grow tent. I have grown three in my balcony, then i took two of them in to the tent for flowering. Third one which stays at the balcony is growing without any problems.

But other two are suffering from light burn i guess. They are in the 4th week of flowering, I have recognised burning parts at the end of week 2. First I stopped giving nutrients for a week, but nothing has changed.

Distance between bulb and top of the plants is 25cm (10"). Temperature on the top is 28C max, generally 26-27C. I think problem is not the heat, it is the lux. I have calculated lux value, it is 179.000 something. I have used this site but i'm very suspicious about the result.


Anyway what can you suggest for bulb height or decreasing lux value. Or even calculate it right at the first place. I have attached a few photos.

In an ideal setting with most lighting, 24" away and up to 75k lux is imo ideal.

Many lighting systems are in a brochure where they say you can be 12" away. Or 18" for example. This may be true and I have had plants that close to strong lighting.

50k lux is a good flowering number. It's enough to grow well.

Thanks mate.

I observe claw leaves at the bottom or middle parts of one plant. I think it is ph or nitrogen toxicity. Well tops may be lightburnt or windburnt still, there is something wrong with soil ph or nutrients. I will recalibre ph meter again, go with %50 of supposed nutrients. Also i took out slightly better looking one and give other one more room and bend a little

Anyway will wait and see