Grow Lights

[urbanfarmer]

I made no claims whatsoever. I simply posted an Internet reference of folks that have had some real life experience with both growing it and going to prison for it.

Are you both having that much trouble comprehending the situation? Just for a moment assume I have a strong knowledge of horticulture, biology, chemistry, and the like. Now go over this thread in your mind. Does anything seem unusual? Hm, what could possibly be the purpose of my actions with such a startling contradiction?

Let's be responsible human beings and realize people are influenced by us when making certain decisions.

Any by the way, this forum is hosted in the USA.

(I had a little fun with the colors )

[urbanfarmer]

Now please stop promoting illegal activities on the forum (even out of misunderstanding).

Thanks for being understanding.

So I guess the idea of a massive aquaponic opium poppy growing operation is COMPLETELY out of the question, huh Urban?
(j/k)

I think most forms of poppy are legal. They sell seeds at my local Lowes!

If I recall CORRECTLY from a lecture given on poppies (yes, we do that here) we went over the history and things, and unless you intentionally get seed that has high levels of opium, you could never get any from the existing cultivars.

[urbanfarmer]

See?

http://www.google.com/search?q=poppy+se ... eeds&hl=en

[JCO]

OK, what do you say folks....let's get back to the subject of this thread and take the ganja growers association info to the SUMP where it belongs.

[urbanfarmer]

OK, what do you say folks....let's get back to the subject of this thread and take the ganja growers association info to the SUMP where it belongs.

I second that motion!

[cookie]

Light intensity decreases x4 every time you double the distance so keeping them more then a foot away is just pissing away electricity.

This idea of inverse square law is a little misunderstood. It is actually the inverse square of the distance "form the light's theoretical point source".

For example, if you have a light array that is two foot square (four square feet) and has an aperture of 90 degrees, then the theoretical point source is one foot behind (above) the light's position. This is found by extending the light pattern to an intersection above (behind) the light. Or, just use trigonometry (tan function) to calculate its position. (1ft X tan(45deg))= 1 ft. The first 1 ft. is half the distance across the light. The 45 degrees is half the aperture angle.

So, if the light is one foot above the grow bed and radiating a given amount of light, then the point source is two feet above the grow bed. By moving the light to three feet above the grow bed the point source moves to four feet above the grow bed thereby doubling the point source's distance from two to four feet above the grow bed. The light intensity is now half and the area covered by this new intensity is four times that of the light's original one foot distance. You have moved the light from one to three feet above the grow bed and halved the light received for a given area.

Starting back with the light at one foot above the grow bed, for an aperture of 45 degrees the new point source is 2.4 feet behind (above) the light of the same size. The new point source is 3.4 (1 + 2.4) feet above the grow bed. In order to double the exposed area you would have to raise the light's point source to 6.8 feet (twice 3.4 feet) or the light to 5.8 feet above the grow bed, thereby reducing the light to half its original intensity at one foot above the grow bed.

It is important with anything other than a single point source, such a a single LED, that the point source of the array be calculated in determining the amount of light and the area that is covered by that light when it is moved away from its target.

My example is for a square array, but if the array is not square or round, but instead rectangular like most fluorescents, then the calculations must be made separately for both dimensions. The aperture will be affected by the reflector behind the lights and will not be the same in both directions.

I realize that I have made this somewhat technical, but if you are serious about knowing how the lighting is changing with position then once you have a set of numbers you can then calculate what the change will be if you move the light.

Or, you can get a light meter and measure it. Be advised, however, that the inexpensive light meters are set for 550 nm or yellow/amber light. LEDs generally emit light at wavelengths other than what the meter can accurately measure. The more expensive light meters come with filters and have either correction tables or an adjustment to compensate for their change in sensitivity to that wavelength.

Oliver

I don't understand your application of the inverse-square law... I think I'm getting the inverse-square law on its own... anyway, why are you treating a light fixture as 2 point sources?

I think the idea is closer is better, yes?

Light intensity decreases x4 every time you double the distance so keeping them more then a foot away is just pissing away electricity.

I think what cookie is misunderstanding is not the inverse-square law, but the concept of units. For instance, if we magically switch to the metric system, then by your implied logic the best distance is 1 meter, correct?

The Truth is 1 foot is NOT the optimum distance. The optimum distance the is the distance that maximizes the light usage for your plant, which will change as the plant grows.

The End!

no end!

I did not misunderstand units. I had fixture at a meter but the DLI meter said there was not enough light per day. If we where metric around here I would have said about 30 centimeters above for a t5 that is pretty well broken in. I used that for cuttings that where rooted and it was sufficient. I also used the same type of lights on tomatoes but put the lights 2-3 inches(about 5 centimeters) as they really liked it close. I do agree 1 foot may not be the optimum distance as plants vary as to how much light they want per day but past a foot never seemed worth it to me according to my measurements. It was more feasible to hang more lights compared to putting them up higher trying to spread the light further.

[Russian Trout 17]

i think LED's are overpriced right now, and that the technology is not where it should be at... after all you scrap the whole unit after its 5-7 years of life. but it is energy efficient, no question about it. its a trade off you have to make with lights, HID's, LED's and T-5s.

[urbanfarmer]

i think LED's are overpriced right now, and that the technology is not where it should be at... after all you scrap the whole unit after its 5-7 years of life. but it is energy efficient, no question about it. its a trade off you have to make with lights, HID's, LED's and T-5s.

That pretty much sums it up. Yep!

I'm partial to T-12's because of the low cost of equipment. The difference in efficiency between a T-12 and a T-5 does not make up for the difference in material costs. The cost per 4' of 40 Watt bulb with ballast and housing and reflector is $6. That's $6 per 3200 Lumens. In Florida, electricity is pretty cheap. I don't know about NY.

[aquaarche]

yeah you can get T12 7000k (blue spectrum) to 10000k(full spectrum) grow lamps for a few bucks and fixtures are really cheap two lamps cover 4X6foot are of your grow bed.

[Russian Trout 17]

vegg florescent should be around 6500 K, while bloom are 3000 K. Ive only used t-5... not too sure about the t-12s if there in the spectrum