Light Distance/Height?

[MichiganAero]

Hello everyone!

I've been browsing the posts for a while, and although its mentioned here and there, I havent found a "guide" if you will. If there is one, point me in the way, and i'll happily read away. As for the question:

Is there a general rule of thumb for light distance from the plants? I know different stages require different heights, just curious what works for everyone else.

My setup is fairly small, 400w MH for veg, 400w HPS for flower.

Attached are a few pics just for fun. (Plants at 12 days)

Thanks!:smokin:

MichiganAero Reviewed by MichiganAero on 11-12-2008. Light Distance/Height? Hello everyone! I've been browsing the posts for a while, and although its mentioned here and there, I havent found a "guide" if you will. If there is one, point me in the way, and i'll happily read away. As for the question: Is there a general rule of thumb for light distance from the plants? I know different stages require different heights, just curious what works for everyone else. My setup is fairly small, 400w MH for veg, 400w HPS for flower. Attached are a few pics just Rating: 5

[bigtopsfinn]

I know this chart is somewhere on this website... I spent some time looking for it but couldn't find it... anyways here it is:

Light to plant distance charts / How far should the light be - Grasscity.com Forums

Keep it range and far enough that you don't burn 'em, you should be good.

[serpentine5]

Rule of thumb.... or hand if you will...
Put your hand above the plant and lower the light until it starts to burn you, then back it off just a bit.... if it burns your skin or is uncomfortable to your hand, it is uncomfortable to the plant....

[headshake]

similar to what serpentine said, but you should be able to hold your hand at the top of the plant for approximately 5 seconds before having to move it because of heat.

-shake

[TheXFactor]

that chart i disagree with (is there anyone on this site that i do agree with???) i highly doubt, and i would great appreciate if stinky followed up my post, but i highly doubt u can safely place A 400w mh 5 inches from plants and it be okay... although that chart did say lumens, not heat... let alone 1000w at 9 inches, but recently i was experimenting with this and i also disagree, if u can hold ur hand their for 5 seconds without being uncomfortable its ok.... but if u held it there for... 10 seconds and it got too warm thats okay???

remember the plant are going to be under the lamp 18-24hrs a day with a simple fan to keep em cool. start out far away with a MH as i remember reading, they are not as forgiving as HPS, but rule of thumb is somewhere between 16-24 inches.. but for those seedlings start it off at 24 inches for the first 2 weeks.... as that plants grow they will grow closer to the lamp, and they themselves will adjust to the light more naturally than u moving it closer then further then closer... I HAD my 400w mh at about 17 inches from my plants, and i think it did begin burning them but i caught very soon,(the same day i moved the lamp closer) and i since brought it back a few inches and the plants are doing fine.. always remember better too far than too close. and keep a fan going on the plants. and fresh air, always.

[PlainJane]

This chart seems reasonable enough.

[attachment=o208359]

[HARDDON]

People make it too difficult.

Keeps the lights as close to the plant as possible without burning the top.

Use a fan to blow heat off the top for even closer positioning.

Get them as close as you can without damaging leaves from heat.

Simple.

I can get a 1000 Watt HPS 10 inches from tops with a strong fan.

[Dutch Pimp]

Metal Halide (MH) light is less forgiving than High Pressure Sodium (HPS).

If you don't beleive me?...put your hand under a MH bulb for 5 minutes...then, you will feel their pain.

[MichiganAero]

LOL. Right now i have the light about 11 inches from the top of the largest plant. I also have a large fan blowing on both the light and plants. They seem to be doing okay.

I think i messed up with one plant thought because one of my droppers came loose and dropped some water on one of the leaves. I know this can burn the plant as water magnifies the light. Its kinda yellowish at random spots on the leave. Thankfully my timer went off before it could do some real damage.

Anyone have any pics of light/water burn so i can compare?

[serpentine5]

Something you need to keep in mind with light/distance is that HID lights put off radiant heat. Meaning that a fan will not lessen the degree of heat, only distance will lessen it. Thats whee the hand over the light method comes in play. Have your fan going, put your hand over the plant, and leave it there. If it is uncomfortable, raise the light.