How Far to Keep Light From Plant... Pics Included

Hey RIU... I started my new grow and i wanted to know how far should i keep my 400W MH light from my seedlings. They just popped up, and right now i have the light about 2 feet about them, just enought so they have a nice warmth on them. is this too close. Thanks in adavance, RickRolled

If you have a light meter, I have read in Jorge Cervantes Marijuana Grower's Bible that seedlings/clones/babies should only have 375 foot candles maximum. I'm not sure how accurate that statement is, but I do know that the small ones need less light, so I'd watch yours carefully. You can pickup a digital light meter in town from hardware or electrical stores. Look for one that can measure a large number of foot candles, > 10,000 or > 20,000 if possible. I picked up an Extech that does 40,000 foot candles for about $180. I'm sure there are many cheaper ones available. Hope this info helps you somewhat..

looks perfect

I would not have an HPS on those to begin with.

Do not place hid lamps over new clones, cuttings or seedlings. You'll kill em or severely damage them. I use 6500k fluorescents in 2 shop lights hung on yo yo hangers for a total of 4 bulbs for the plant's first 2 weeks. then go into veg with at least 4 hours of darkness each night for the first week before cranking on the nutes and 24 lighting.

OK so i strung up some CFL's 4 23W (100 watt equivent). Are they getting enought light now?. Thanks for the help +rep all above

looks good, im sorry but i cant agree with people saying to not put seedlings under hps, they grow outdoors with the sun that is muchhhh stronger with no issue, ppl are a little too anal sometimes

RickRolled said:

OK so i strung up some CFL's 4 23W (100 watt equivent). Are they getting enought light now?. Thanks for the help +rep all above

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Looks great man! I know you won't have a problem with using those 4 CFL bulbs for the first 2-4 weeks. Here's what I'd do, granted I'm relatively new, but I'm keep them under the CFL's as you have them now for 2 weeks. Assuming they look healthy and are doing well, I'd move them to the EDGE of your 400w HPS lamp...NOT directly under, more like on the outskirts/side/edge off the main light underneath the reflector. Keep an eye on them there closely. Keep them there a week. Move them closer. Repeat. Just keep an eye on them. If they get leggy/stretchy, use more light. If they get heat stress or a burn, use less light. Ramp it up slowly.

Hope this helps..

i was wondering this same thing but with cfls..how far away should you keep 26watt cfls from 1-2week old plants?? is less than a foot to close?? like 6inches?

diamonddave said:

looks good, im sorry but i cant agree with people saying to not put seedlings under hps, they grow outdoors with the sun that is muchhhh stronger with no issue, ppl are a little too anal sometimes

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Its not that we are little too anal its that in the early stages of a plants life care must be taken to not introduce them to too much heat or too much intense light.

It is not impossible to get seedlings to grow under HPS but using CFL's means you can concentrate on creating a thriving root zone before getting them under HPS.

Most people dont raise their lights up high enough using HPS when trying to grow seedlings underneath them and generally cook them due to too much heat.

I personally use 24w 6400K T5 for 10days and then
200w ECO CFL for a further 10-15days then

under my 600w HPS.

Like i mentioned its not impossible to do but most dont raise their lights high enough and if they do then the seedlings can stretch for more light if you arent carefull which is why alot of people opt for CFL's to get them stared.


J

Canabian420 said:

i was wondering this same thing but with cfls..how far away should you keep 26watt cfls from 1-2week old plants?? is less than a foot to close?? like 6inches?

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I keep my 24w around 1-2inches away

My 200w i keep around 4inches away and have a fan blowing at the bulb to remove any heat from the 200w ECO CFL away from the plants..


J

diamonddave said:

looks good, im sorry but i cant agree with people saying to not put seedlings under hps, they grow outdoors with the sun that is muchhhh stronger with no issue, ppl are a little too anal sometimes

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When we grow indoors, we are providing our plants direct light for hours on end. There is no shading, clouds, or periods of extreme horizontal placing of light sources, as is the case with outdoors. Young seedlings and fresh cut clones do not have the ability to weather 18-24 hours of direct intense light. Unlike inside, outdoors plants get breaks with clouds, shade, and the fact that the sun isn't overhead all day long like it is inside a grow room.

Maybe if you weren't so anal retentive, you would be able to think outside the box and come up with reasoning like this on your own? People aren't being anal, thy're passing along experience.

Serapis said:

When we grow indoors, we are providing our plants direct light for hours on end. There is no shading, clouds, or periods of extreme horizontal placing of light sources, as is the case with outdoors. Young seedlings and fresh cut clones do not have the ability to weather 18-24 hours of direct intense light. Unlike inside, outdoors plants get breaks with clouds, shade, and the fact that the sun isn't overhead all day long like it is inside a grow room.

Maybe if you weren't so anal retentive, you would be able to think outside the box and come up with reasoning like this on your own? People aren't being anal, thy're passing along experience.

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WELL SAID !!! gotta give a +rep for that one !!!!


J

Serapis said:

When we grow indoors, we are providing our plants direct light for hours on end. There is no shading, clouds, or periods of extreme horizontal placing of light sources, as is the case with outdoors. Young seedlings and fresh cut clones do not have the ability to weather 18-24 hours of direct intense light. Unlike inside, outdoors plants get breaks with clouds, shade, and the fact that the sun isn't overhead all day long like it is inside a grow room.

Maybe if you weren't so anal retentive, you would be able to think outside the box and come up with reasoning like this on your own? People aren't being anal, thy're passing along experience.

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im not being anal retentive, i am merely saying that it is def possible to use the hps for the seedling stage, keeping a light 2 feet above the seedling is not going to harm or burn the plant when there is good ventilation present.. as i am passing along my knowledge, i use hps all the way through with fantastic results (even in the seedling stage), i am able to think outside of the box, thank you, dick

Serapis said:

Do not place hid lamps over new clones, cuttings or seedlings. You'll kill em or severely damage them. I use 6500k fluorescents in 2 shop lights hung on yo yo hangers for a total of 4 bulbs for the plant's first 2 weeks. then go into veg with at least 4 hours of darkness each night for the first week before cranking on the nutes and 24 lighting.

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"You'll kill em or severely damage them.", sorry but no, it is def possible but to say that it will happen is just ignorance

diamonddave said:

"You'll kill em or severely damage them.", sorry but no, it is def possible but to say that it will happen is just ignorance

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I agree slightly with you.

It is possible to do what you are talking about. But like you said as long as all the other factors are taken into account such as ventilation.

The main reason alot of people do not use HID when rooting clones or growing from seed is that the amount of light intensity coming from the HID's can cause the plant to bolt and stretch instead of creating a root system.


This is the main reason people use CFL's of low wattage in order to keep the clones or seedlings ticking over while they develop their root system.


J

jondamon said:

I agree slightly with you.

It is possible to do what you are talking about. But like you said as long as all the other factors are taken into account such as ventilation.

The main reason alot of people do not use HID when rooting clones or growing from seed is that the amount of light intensity coming from the HID's can cause the plant to bolt and stretch instead of creating a root system.


This is the main reason people use CFL's of low wattage in order to keep the clones or seedlings ticking over while they develop their root system.


J

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Exactly!!!! +REP.... And why waste all the precious power lighting up a 600w or 400w light when all you need is 1500 lumes oe so? Seems like common sense to me Diamond Dave.... And before you go calling others names, you did start it with your anal remark. You are the one that is not thinking this through.

HID lamps at 2 feet away do little more than waste energy.

Think about it. First of all there is the light provided. Most HPS bulbs are 2700K color temperature with the specific wavelength peak about 30nm off of ideal. Essentially, 10% of the energy provided by the bulb is photosynthetic active radiation. Add in the fact that the bulb is a distance of "3 units" away when at 2 feet and you'll see that the plant is getting 10%-12% of the 400w due to the law of squares. Finally consider that a small seedling might be 2"x2" large, for a total area of 4 square inches, but the light is spread across an area of say 576 square inches (a 2 foot x 2 foot space with reflective walls). So the plant takes up 0.7% of the total area, and cannot get to many of the photons that are lighting other parts of the room.

Now add that all up, you are getting 0.7%, of 10%, of 10% of 400w. Or approximately 0.028 watts of energy is being actively absorbed and used by the seedling, and that's on a good day with full bore photosynthetic action. In addition to all this, of the wavelengths being absorbed the majority is red. Red light triggers flowering hormones and increases the stretch between internodes.

Now think about all that power versus a 27w Day Light CFL bulb in the 6500K color temperature kept at within 2". You are at a factor of about "0.8 units" from the bulb, so you're getting more than the advertised lumens that close. Lumens are a poor way of conglomerating all the effects of light but simply put: more is better. So you're sitting at 100% of the wattage, with more than 80% of the energy available for photosynthetic absorption in the highly reactive blue part of the spectrum that encourages leaf growth and decreases internode distances. Then consider with a clamp light reflector you can direct your lighting to an area no larger than 9 square inches, increasing the amount of light the plant is able to absorb to close to 50%.

So... you make the choice...
0.7% of 10% of 10% of 400w for 0.028 watts to the plant
or
50% of 80% of 100% of 27w for 10.8 watts to the plant

An increase of 385 times the energy to the plant with less than 7% of the energy used.

Talk about a no brainer. An HPS light that provides so little energy AND causes my plants to stretch from both the distance and the wavelength or a lower wattage CFL bulb (purchased for less than $10) that forces plants to be bushy and stocky due to close proximity and wavelength. I mean, there's a smart way, and there's the other way.

Now, that isn't to say that a CMH bulb wouldn't be better, or maybe a metal halide or an HPS in the appropriate spectrum (2100K to 2300K). There are variables to consider, but light is physics, physics is math, and you can't argue with numbers. It's science. Scotchy, scotch scotch!

Snow Crash.....


I'm impressed!

+REP

From my recent experience I placed my 600w mh on two week old plants about 12 inches away. I have a cool tube with good ventilation so heat wasn't an issue. The plants were getting really light green and hardly growing, so basically the lights was bleaching them out. I was also on a 24 hour light cycle (on all the time). I raised the lights to about two feet off the plants, went to a 20/4 cycle and presto, they started growing and are now back to a nice healthy green color. Next grow I will use t-8 flouro's for the first two weeks. You basically waste the electricity with the MH lights and either way they will grow about the same. Once the plant enters into the third week they will need the MH or equivilent for their rapid growth spurts.

Anway, to answer you question, back off on the distance and you'll be glad you did.