How high do I keep my light

[abadtrip]

I was just wondering how high off my plants I should keep my 315 cmh I just switched to 12 12

[D.A.A.S.69]

Man that's a good one ,that's what I'm getting next month ,I think their supposed to run lots cooler, but I don't know how high to hang it , several people on GWE has got them though and they will tell you.There about 500 bucks ain't they.

[Sammy]

I keep mine at 22 in watch for leaves curling up.

[DrPhoton]

Light height is not a huge factor, the biggest thing with height is controlling the distribution of light. When it comes to a certain light source, the number of photons leaving the source is the same that reaches the destination. Many people do not fully understand light relationship with inverse square law, i had to actually read a few photography and filming forums to realize how bad.
Commercial growers have their lights situated several feet from the plants, in tandam with many others. With several lights, the light overlaps and diverges evenly. Allowing for a greater uniformity that you would not typically see with lights that are close, regardless if there are one or many lights. You also get a greater vertical uniformity because of the greater distance from the light source, allowing for better penetration into plant canaopy. The added distance of the lights does not loose any energy or effeciency, photons do not reduce in number over distance. They diverge, continually filling space, reducing density the further they travel. Its not until they hit matter that the energy is converted into other energy such as heat. This is where reflective losses come in.

The biggest thing with light distance is controlling the uniformity over the grow area, both virtically and horizontally. But ultimately the total light output capacity is going to dictate your yeild, the control of the light is going to dictate how the light distributes the photon energy over your plant.

Danny.

[Little]

Thank u for the info

[abadtrip]

That's awsome thanks for the info I have mine at the top of my tent I never brought it down during veg so I'll leave it alone

[DrPhoton]

I do have to add that, this does not mean you can have a light source at any height. Like i said the distribution of the light has to be taken into consideration. If you have a light source too close, photoinhibition can cause slowed growth or cell death. If the light source is too high and or reflector angle too wide, efficiency can go down because of reflective losses. This is of course assuming a walled off enviroment is used.
A good place to start is high, then introduce lower until you reach a good light projection over the canopy or negative response from plants.

[oldjarhead100]

Wow Danny thats good info Boy do you do your homework. I would like to add that after reading Nebulas tutorial on light I purchased a lux meter since pot plants can't use anything above 85,000 lux I found that I could get all of my kolas under the best amount of light for them without burning, I try to keep the canopy even but after buds start growing they do get a little different height so with the lux meter I can keep my light far or close to give the girls the best light I can.Lux meters do not work for leds though

[DrPhoton]

Yes a lux meter is a good reference tool, i too purchased one after reading nebulas article. I then made a quantum PAR meter with a certified apogee sensor.

https://www.apogeeinstruments.co.uk/...uantum-sensor/

Being a electrician i have plenty of multimeters on hand, hardwired the sensor to one and wop de do. I have a Quantum PAR meter for less than $170 US.
The sensor holds all the technology for measuring PPFD, all you need is a electrical meter to read the values. It so happens the voltage received just has to be multiplied, just like on your typical lux meter.

Just for some more information, a plant can limit its photosynthesis rate or quantum yeild with photoprotection. This is a stage before photoinhibition that trys to limit its ability to receive photons to protect itself from further damage. This can be in the form of leaf positioning, increased cuticle layer protection, chloroplast repositioning etc. But the plant will not present any symptoms under this process, other than the obvious leaf movement. So having plants as close to the light, just far enough that does not show signs of stress or damage might not mean that it is operating under optimum or efficient conditions. I have read about a couple of people who have had their lights as close as possible without distress. They were told to raise the lights and found that their yeild actually increased. Likely because they were putting their plants into stress without them knowing.

I personally like to run my lights around 700umols or 60,000 lux.

[abadtrip]

Well I am going to get a light meter now arr I have no idea what I am doing. Thanks for all the info guys I hope I don't fuck shit up but it's allways an option