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More info about lighting

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First off, here's a link to an article that explains the relationship between Lumens, Footcandles, Lux and candlepower.  I've found it helpful:  http://www.energybooks.com/pdf/D1150.pdf Another little helpful conversion is this:   1 fc = 10.76 lux 3,000 fc = >30,000 lux Avg outdoor sunlight ~50,000 lux = ~ 50,000/10.76 = 4,647 fc (Note that this is 'average' outdoor sunlight.  At noon on a clear summer day, sunlight intensity is generally around 10,000 fc.)   Some additional things I'd like to add about lighting...   Many sites say give them at least 4 hrs of direct sunlight. Others say use indirect light. Considering how pale mine get with high light levels (and many hours of light per day) I would be flexible and just watch how the plants look then make any adjustments. I think I tend to overdo it on the light levels because I'm used to having plants that require many hours of very intense light and I have to provide this all winter or they die.  I was giving 3000 footcandles of light per day to my VFTs, but that started to seem excessive for an 18 hr day so I raised the lights a few inches and now they get 1000 fc which seems ok, plus I don't have to worry about even the little heat from the fluorescent lights. Remember, infra red (heat) is also a form of light and will be focused along with the visible light when the bulb is put into a directional reflector. I have a simple light meter that measures in footcandles.  Normal indoor lighting may not even register on this scale even though it looks plenty bright to our eyes but that's because our eyes and brain can adjust and become accustomed to the light around us.  Full mid-day summer sun is 10,000 fc (full scale). This is how I measure. It is unfortunate that when you look at a bulb you want to buy, the light output is listed in lumens and there is no conversion from lumens to footcandles. Many long straight fluorescent bulbs have high lumen ratings (i.e. T5), but that is the total light output, not how much is going to fall right on your plants (which will end up being a low footcandle number.) That's why I use the spiral compact fluorescent lights. The lighted area is concentrated in a small-ish volume and they can more easily be fitted into a conical-type directional reflector to beam the most light right where you want it. That's how I can get sometimes over 4000 fc from a 300 watt compact fluorescent light using only 65 watts of electricity. I make my own fixtures to be able to position the bulbs as close as possible to the reflector's best focal area. Another very helpful tip to increase your light intensity as much as 20% without using any more bulbs or electricity is to surround your growing area or the open of the light reflector with a reflective material such as aluminum foil or aluminized Mylar.  These intercept light rays heading out to the side and re-reflect them back in towards the plants.  I did this one with cacti one year and they grew better in an aluminized box indoors, all winter, than they did outside all summer. Reflectors: Most reflectors are only approximately parabolic shaped.  I've seen plastic flower pots with more parabolic shape than a metal light reflector.  So look around at anything with the general shape and size you want.  Keep in mind even a great reflector will not give high intensities if it is large.  Look for something small that you can still fit your bulb into.  Without doing a lot of angle measuring with Photoshop, the easiest way to locate the best focal area of any dish-shaped reflector is to cover the inside with silver paint, or, my favorite, aluminum tape found in the heating and air conditioning areas of hardware stores.  Make a hole in the bottom center of your reflector which you can stick a pencil or anything through.  Turn on a bright light (preferably without a lampshade) at a distance from your reflector (at least 10 feet away.)  Aim the reflector toward the light and put the pencil through the hole in the back of the reflector.  When the reflector is aimed right at the light and the pencil is perpendicular to the base.  the parallel light rays from the light will focus to create a bright area on the pencil.  Most focal areas are not points like in math books, they are a much more general location, but nevertheless, that will be the best place to position the brightest area of your bulb.  You will definitely have to use your imagination to find ways to connect your reflector (whatever it is) to the proper electrical boxes, and conduit and have a built in adjustment to hold the bulb in the right position. I'm not even going to try to cover here all the safety issues about grounding and ability to withstand heat when using plastic parts.  I've been doing this for 8 years so if you have a question, just email me. For round bulbs use round reflectors.  For a long tube, the standard fluorescent reflector is useable, but not the best.  A more efficient design is called the "M" reflector.  It looks like a MacDonalds double arches logo.  It is 2 long reflectors that meet in the middle and that's where the light bulb is positioned.  These can utilize light that is normally lost by going "backwards" from the bulb and not toward the plants.  But construction is difficult.  You're better off looking for round reflectors. Spectra: As you know, the sun's spectrum is continuous.  Coincidentally, the absorption spectrum of the various chlorophylls, carotenes, xanthans, etc. also tend to be wide curves (for different reasons) but it means that even if the plant sees light that is not exactly at the frequency where its maximum absorption is, it can still absorb some of the light.  This makes it more efficient.  Nature is like that.   The only continuous spectrum device we have is an incandescent light and these are going the way of the dodo.  When we make light with fluorescent's or LEDs, the light is not continuous.  It has a lot of peaks and valleys both due to the atomic transitions of the electrons in the arc of the gas used and also the types of phosphors used which turn (usually) ultraviolet light into whatever other color we want. To our unaided eyes, the color can look continuous, but it's not.  Companies are working on using multiple phosphors to make a more continuous light spectrum, but we're not there yet and it does raise the price.  Your typical fluorescent, HID, or LED light can gave some continuous spectrum, but it's probably minor.  Most of the spectrum consists of spikes of varying intensities at various wavelengths.  Yes the plant can use these spikes because the chlorophyll , etc., absorbs a wide range of wavelengths so we manage to get by using intense spikes instead of a more gradual, lower intensity spectrum (probably with less heat) that the chlorophyll could absorb just as well.  Maybe in a few decades we'll have perfect light sources like this. As for those purple lights that emit the red and blue absorbed by the chlorophyll, they are not worth the cost.  Having green light included in the light output does not detract from the chlorophyll efficiency.  It just doesn't absorb it in the first place.  It is just reflected away.  That's why leaves look green.        
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Guest Wednesday, 11 December 2019

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