Profound

I found this over at angelfire.....
I remember when I was searching for light info I could find it easily but sometimes not as complete as viewing a few threads at HC.
Now that we've grown to GC.com....Im assisting those who seek lighting info just like I was......

Enjoy....

www DOT angelfire DOT com/cantina/fourtwenty/yor/lightres.htm

Lighting's impact on the value of indoor cannabis yields is more than significant. It's not only the primary driving force behind the weight of our yields, but also the density of the yield per square foot that gives shape to the weight. Light is a broad topic to be sure, and with many of its challenges being double-edged it's not surprising to find light and space resources bound to one another by their mere coexistence. With any given lamp, as a space grows larger its light intensity grows weaker. As shown in the graphic to the left the relationship is direct and unbending. Although gardens can be found varying anywhere from one extreme to the other, there are losses and gains challenging a grower from each side of that seesaw, both in the weight of the harvest and in the weight of his satisfaction from its other traits. Yield alone is not the end-all if one doesn't find a harvest appealing in other ways, nor is appeal the end-all if yield isn't satisfactory, somewhere in the balance we each find our own personal brand of gratification.


While trying to keep these challenges in perspective we'll examine such topics as available light, lumens, foot-candles, distance, sweet spot, footprint, total yield, density and yield per square foot to name a few. Once understood, it's hoped a grower will be better able to combine the focus he gives his space and light resources with density related esthetic values he expects from his harvest.

Available Light
Available light is the lumens available from your lamp to be distributed across your plant's canopy. It is not the light striking your canopy, which is measured in foot-candles (fc) at the canopy. Available light is a measure of lumens at the source, while foot-candles is a measure of lumens at the target. Between these two points light is lost to empty space or objects that don't reflect light, for the production minded indoor gardener that translates into lost growth and yield. Lamp-to-canopy distance and your choice of reflectivity preferences will ultimately determine the light your plants receive.

Because cannabis is a high energy sun plant most indoor cannabis gardens have the available light very tightly focused, more so than gardens used for conventional indoor produce (vegetables, herbs, etc). As a result, indoor fc levels approaching that of the most intense sunlight can be reached or exceeded by growers, but can damage plants if heat from the lamp doesn't do more damage first. The most light intensity plants are likely to see in nature is around 10,000 fc, and for only a couple of hours during the day while the sun is directly overhead. For artificially lit plants, above 9,000 fc is considered shaky ground by many indoor growers, either due to the potential for damaged growth or for the more watchful eye needed to prevent it.

The YOR uses Available Lumens per Square Foot as a measure for the average available light distributed across a space. While this does address the space's average lighting, it does not reflect the closest safe-point when dealing with real lamp-to-canopy distances, nor does it reflect the furthest distance at which light can be used effectively.

Distance and the Sweet Spot
Every top-lit indoor garden using artificial HID lighting has a sweet spot located directly under the lamp, where it's closest to the canopy. If not accounted for in your plans to distribute available light, fc in the sweet spot can far exceed that of the sun, especially when lamp cooling technologies are used to reduce normal distances limited by heat. Finding the limits of your coverage area implies a compromise between the minimum light levels at the outside edges of your area (furthest from the lamp) and the maximum light level at the sweet spot (closest safe-point to the lamp). The happy medium is not to overdose the sweet spot with too much light (or heat) and to distribute enough light to the outside edges of your grow space for acceptable growth. The controlling factor for both of these limits is the height of the lamp above the canopy. Reflective surfaces surrounding your garden will help reduce light losses at the outside edges, but light at and below the sweet spot is controlled by distance between it and the lamp. The table below gives an idea of the distances involved, fixtures used during the meter readings are common to indoor gardens.

Approximate fc in the sweet spot
(metered directly beneath the bulb)
Lamp Distance Foot-Candles
1000 watt HPS 1.50 foot (18 inches/45 cm) 9,000 fc
600 watt HPS 1.00 foot (12 inches/30 cm) 9,000 fc
1.50 foot (18 inches/45 cm) 5,600 fc
400 watt HPS 0.75 foot (9 inches/23 cm) 9,000 fc
1.50 foot (18 inches/45 cm) 4,000 fc
250 watt HPS 0.58 foot (7 inches/18 cm) 9,000 fc
1.50 foot (18 inches/45 cm) 2,800 fc
Highlighted items approximate the closest distance that particular lamp should be to the sweet spot to avoid over-lighting. (those interested in photosynthetic radiation can use this PPF PAR converter.)


Footprint And Coverage Area
It's important to know what the usable footprint for your particular light fixture will be at those distances, fixtures often vary from brand to brand. A good footprint test is to hold a lit fixture above the floor, at various distances, while measuring the strongest light pattern shone on the floor. A safe compromise between over-lighting the sweet spot and under-lighting the periphery is reached when the lamp is slightly above its closest safe-point distance, while its strongest light pattern still covers the preferred garden dimensions.

The following graphics are of a square lamp fixture being used to create three footprints of varying sizes, they illustrate the interplay occurring between lamp height, canopy size, over-lighting and under-lighting.



One might wonder why the example on the right wouldn't be acceptable if the canopy space was made smaller to eliminate the under-lit periphery while the fixture was still left hanging high. The closer a lamp is to the top of the canopy the deeper it will penetrate into the sub-canopy, and the deeper the usable harvest (yield) will be. When a lamp is hung higher than it needs to be its effective downward range is reduced according to the Inverse Square Law for light intensity. As a result, the depth of the usable harvest will suffer, and because the canopy top will receive less light overall, it will produce less as well.

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choader

Great post!! Agree wholeheartedly.

And the limiting factor to lumens is usually ventilation. Solve ventilation/heat in a big way (more than you think you need) and you have all the options necessary to cram the lumens in (within reason and as stated in your post).

This is why I always start with ventilation design in my cabs. The rest falls out from there.

Choader

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Profound

Wisely put Choader.....
Did you load the site and give a view to the diagrams and all ??

Here's something else I picked up. It was created by a Gardener named CaliGrower
I lighting chart....

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ghostsmoke420

i like that one to that is a great one. im glad you found that i was alway wondering how much fc my light is giveing my plants and how far away to put them good find that is something for everone to save

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If at first you don't succeed, try to grow some different weed




Basic cheat sheet:
Ec goes up, PH goes down=plants require less nutes.
Ec goes down, PH goes up=Plants require more nutes
Ec stable, PH goes up=Equilibrium=Good thang.
-OldPhart

choader

That's a great link Profound. I did look at the graphics. Although from my experience, it seemed I could get closer than that article predicted. I have a 600W HPS and I was within the 1' mark without issue. Not sure how close but this sure gives you a good starting point!

Again, great link dude!

Choader

__________________
SS Bubblegum & DP Mazar Small Cab - Complete
Choader's 600W HPS Grow - Complete
Small Cab Grow - Complete

READ ME!! Posting Guidelines
Male and Female Pre-Flowers

Profound

To complete the info above ....I found some Info posted by a Gardener named "Told" at another site.
It shows the Metal Halide and the percentages of them all.
I'm too late on the edit button so I can't add it to the above but .....

If a MOD could consolidate the charts in one post it would look 100% better. Thanks in advance.

Attached Thumbnails

   

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old_greg

Thanks for all the useful info PRO.. lets me know that with the cool tube on that 150HPS, i don't need the 250 or 400. the babies are gonna love this Chit!!

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SirTokeAlot420

Damn Pro I was gonna give you some rep for this kick ass post but I have to spread more around first. Very very useful info. Cheers!

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