Why 30" From Light?

[ProdigalSun]

I regularly see people posting that they are keeping their 1,000 watt lights ad distances of 20 or 30 inches from the plant tops. Why do people do that? I have a 1kw HPS and the plants (including a sprout from day 1) are about 12-14" from the center of the filament within the bulb. My temps are in the mid 70's in the room, and the area right at the plant tops is never allowed to go above 85*F.

So Why so far away?

 

[jswett1100]

I cant say ive really seen any post about that. but i guess 12-14 would be fine probley 12-8 too

 

[amgprb]

I have learned, since recently moving from a 400 to a 600, that there really is a possibility of light toxicity! I used to keep my 400 6-8" from my canopy, so w the 600 i went to 10-12" and eneded up bleaching my plants. Have to keep the 600 more like 14-16" off of my canopy.

 

[ProdigalSun]

I have never experienced any bleaching, even under a 24 hour schedule, what does that look like?

 

[Jimdamick]

You have a really cool 1000 watt that will produce 85 F at 14". Mine is more like 100. If you want more light spread, and cooler temps, that is why you want 30". I never go below that. Merry xmas

 

[Jimdamick]

I have never experienced any bleaching, even under a 24 hour schedule, what does that look like?

the leaves will turn white

 

[Doer]

I regularly see people posting that they are keeping their 1,000 watt lights ad distances of 20 or 30 inches from the plant tops. Why do people do that? I have a 1kw HPS and the plants (including a sprout from day 1) are about 12-14" from the center of the filament within the bulb. My temps are in the mid 70's in the room, and the area right at the plant tops is never allowed to go above 85*F.

So Why so far away?

Light burn is real. Not heat. The photons at that energy, are harmful. I have let plants get up to a water cooled light. Not much heat at all.

Here is what happened. It ruined it. I couldn't get it to cure properly and it tasted...un-smokeable. And I have smoked pocket lint.

I BHOed it and recovered a lot of good oil. So, not really a total loss. But, you don't want to burn it. Here is bleaching. Notice how the tricomes are fried.

 

[Dogenzengi]

I light burned/ bleached my tops on my first plant.
it all goes back to the hand test, if you can hold the back of your hand under a light
at a given distance for 30 seconds then it's OK for your plant.

my hood causes a hot spot so I have to do my hand test directly below the base of my bulb.

In my situation the "hot spot" caused by my horizontal bulb in my hood is a big culprit to light burn.

Now I have it so I can turn my plant in my tent so I can change the hot spot to a different location on the plant.
being unaware of the hotspot caused me to hand test the wrong place under my hood!

I am on Strong meds so if I typed weird it's the drugs, but hopefully you get my point.

 

[amgprb]

I light burned/ bleached my tops on my first plant.
it all goes back to the hand test, if you can hold the back of your hand under a light
at a given distance for 30 seconds then it's OK for your plant.

my hood causes a hot spot so I have to do my hand test directly below the base of my bulb.

In my situation the "hot spot" caused by my horizontal bulb in my hood is a big culprit to light burn.

Now I have it so I can turn my plant in my tent so I can change the hot spot to a different location on the plant.
being unaware of the hotspot caused me to hand test the wrong place under my hood!

I am on Strong meds so if I typed weird it's the drugs, but hopefully you get my point.

Even the hand test is only an indicator. My 600 cooltube, i can keep my hand 6" away without any issues. I think that is more for heat stress issues. I dont know if there really is any sort of "test" for light toxicity

 

[amgprb]

I have never experienced any bleaching, even under a 24 hour schedule, what does that look like?

It turns your leaves white/grey/beige, frys the trichs and will even turn the calyxes white. After the damage is done, even if u move the lights up, all of the infected area - the leaves and plant material will get crispy and almost appear dead a few weeks later.

 

[Doer]

Only the cube root of the distance is your tool for calculating photon energy spread density. At what point is it something that approximates sunlight?

Let us say, 30" for 1000w.

That is why "they say" it, actually. Science. Botany. Biology.

 

[qwizoking]

""test" for light toxicity"
....light meter.....sun throws an avg of 7k lumens per sqft 10 consistently can bleach(the sun at its strongest)...or 120,000 lux if your weird
I keep my 600 watt 8-12 inches and actually want slight bleaching on some of my plants.
Light bleaching is very different than wind/heat/nute burn
It is real and does correlate to your nute ratios and even air/co2 but occurs when your plant can't keep chlorophyll production at rates necessary for that level of photosynthesis. Try and optimize that first ..you can't just up the light and expect the plant to miraculously follow suit...but they can and do adapt..to an extent

 

[ProdigalSun]

Only the cube root of the distance is your tool for calculating photon energy spread density. At what point is it something that approximates sunlight?

Let us say, 30" for 1000w.

That is why "they say" it, actually. Science. Botany. Biology.

Wow that went right over my head. Math was my D'Angelo Bailey in school.

 

[ProdigalSun]

Is bleaching the first symptom of having the light too close?

I don't mind moving the light away, if it's going to help my plants but it seems to be counter intuitive to do that when I just spent money to get more light by upgrading from the 600w to the 1kw light.

 

[Jack Harer]

You have a really cool 1000 watt that will produce 85 F at 14". Mine is more like 100. If you want more light spread, and cooler temps, that is why you want 30". I never go below that. Merry xmas

^^^^^I keep mine at about 18 or so in. I can put them closer, but like Jim said, I feel I reach a point of diminished returns in that the closer you get to the tops, the smaller the footprint of the light. Less coverage aint good either. I've never had the girls burn, or bleach out. 30 in is fine though to ensure good coverage.

 

[ProdigalSun]

Ok I'll move it up, but it still seems like a wierd thing to do. I thought that the heat was the limiting factor.

This is my bulb. I'm running a Lumitek ballast at 1,000 watts. I don't like the Super Lumens thing, seems like a gimmick.

http://4hydroponics.com/1000w-ultra-sun-hps-lamp

 

[ProdigalSun]

I would do the math to determine the distance in inches, but I haven't got a clue how to do that high level arithmetic.

 

[Doer]

psssst....the answer is (30).

 

[Doer]

How about this? (because, today is Yogi Diesel Day).

Use the face test! At what point can you just begin to open your eyes? 30 inches.

(face test not real, do not do as directed, do not try at home, do not expose eyelids to close HID, never expose eyes at 30 inches without eye protection. no joke)

 

[ProdigalSun]

Oh geez man, I try to go out of my way not to look at that thing.