Yes we do have a very different view of the zones. Mainly for me, that is because I think the USDA zone map is "somewhat" useful in a limited way if I apply it to plants that I want to landscape my yard with. Its a "loose guide" for me, no more, when landscaping. Mainly because it only deals with COLD temps. You have to use a separate criteria for HEAT here in the South. There's no one map. I think that's a shortcoming. I know a separate heat index map does exist. But as far as the USDA zone map is concerned, I find it a lot more useful for my greenhouse. I am in zone 8B. However, I am still able to grow many plants in my yard that are supposedly only labeled for zone 9 and above. If I gardened by what books said about the zones certain plants would live in, and paid attention to the zone maps, I would be shortchanging myself on growing a lot of neato plants that actually do very well here. I do find the concept of "zone" imminently useful inside the greenhouse though. I have plants growing and blooming in a zone 11 environment that are supposedly "zone 10 and above" plants that friends of mine in South FL zone 10 have not been able to get to bloom in their yards. I have to wonder, if I turned down the heat, would they still do as well? Probably not. When I first moved to FL in the very early 1990's from Los Angeles, I was stunned at all that could be bloomed here, in the ground and even just in CONTAINERS in my zone 8B, that could not be bloomed in the zone 10-11 So Cal environment. Certain gingers, heliconias, vines, orchids, they will do so well here even if you have to stash them in a freeze, and they wouldn't do well in So Cal even in a "frost free" environment. I asked "Why?" many years later on a forum that was heavily weighted with West COast people, and the answer seems to be "heat accumulation". Even though So Cal where I lived was a zone 10-11 and rarely if ever actually freezes, its too cold at night most of the year, and too cool in the day most of the year, to afford the continuous heat needed by certain plants to thrive and bloom. So when I set up my greenhouse, I had to think, "How do I want to do this?" Because actually, In FL, its much harder to cool the greenhouse in summer than it is to heat it in winter. I decided that I wanted a "conservatory style" planted greenhouse instead of a greenhouse that had benches to set stuff on, and that if I was going to go to that type of setting, I wanted it to be a jungle with everything that I could never leave out all year here. So if I was going to commit to THAT, I decided, zone ELEVEN conditions were what I wanted. Anything that can take a zone 8B winter, even if it goes dormant and comes back as a "perennial", or gets leaf burn but survives, does not merit the zone 11 greenhouse. Only stuff that would never bloom or live in zone 8B, or is expensive of somewhat rare, gets to be in the zone 11 greenhouse. Maybe that's a simplistic attitude on my part. I don't pay a lot of attention to how much it costs to run the greenhouse. I only keep records for tax purposes, because I do run a small mail order plant business and have to report income and expenses. If I was a huge business entity I would probably think I needed to have a more formulaic approach to the greenhouse, but I'm just not. I admire people like you who have all that scientific stuff going for them. Its just not my focus. I'm more into just cranking up some Blue Eyed Christ, getting out the fertilizer and piddling around in my greenhouse. I don't like to think about it too much.

Let's assume you fill the boxes with sand. Keep in mind that sandy soils have a higher bulk density than nearly anything else you would fill these boxes with, including clay. Clay IS NOT HEAVY; clay is cohesive. It sticks to itself so that it only feels "heavy" when plowing or otherwise working the soil. But I digress, build the structure strong enough to fill with sand, and you should be ok filling with anything else. Let's first make some assumptions. We'll say the bulk density (dry mass of soil/total soil volume) is 1.7 g/cm3. This is typical for single-grained structureless sandy soils. Second assumption: particle density (dry soil mass/volume of the solids) is 2.65 g/cm3. This is a typical estimate for the particle density of sands, which is essentially quartz. Knowing these assumptions and the total volume weÂre dealing with, we can calculate the total mass of the solids, total pore space, and the mass of water that will fill that pore space when the soil is saturated. OK, calculate the volume of the boxes. 8 ft x 2 ft x 2.5 ft = 40 ft3. If you have four of these boxes then you have 4 x 40 ft3 = 160 ft3. If you fill these boxes to 1.7 g/cm3 with sand, the total mass will equal the bulk density times the total volume. First, convert your units to metric. 160ft3 x (1m/35.31 ft3) = 4.53 m3. Now you can calculate total mass of the solids. 4.53m3 x 1.7g/cm3 x (1kg/1000g) x (1,000,000 cm3/m3) = 7701 kg. So, all that sand in 160ft3 at a bulk density of 1.7 g/cm3 will weigh 7701kg when completely dry. That will never be the case though. If the soil becomes saturated, then all the pore space will be filled with water. We can calculate the total pore space and, assuming the density of water is 1 g/cm3, calculate the mass of water filling those pores. Total pore space is equal to one minus the quotient of bulk density over particle density. Porosity = 1  (1.7 g/cm3 ÷ 2.65 g/cm3) = 0.358. This number means that for every 1 m3 of total soil volume, there is 0.358 m3 pore space. Just multiply the porosity and the total volume and you get the total pore space. 0.358 x 4.53m3 = 1.62 m3. The density of water is 1000 kg/m3. 1.62 m3 of water would then weigh 1620 kg. Add the mass of the solids and water, 7701 kg + 1620 kg = 9321 kg. There are 2.20 lbs per kg. 9321 kg x (2.20 lb/kg) = 20549 lbs. I would say thatÂs the maximum mass you should expect from your solids at saturation. Keep in mind that I study soils, not engineering. Speak to a license engineer about how to best support your roof safely.

Okay, I gave it a shot. You didn't mention the wattage, efficiency, or light output of the HPS fixture. If I knew that, I could try to figure out the lumens of X output on a 81Sq.Ft. target 12 ft away. But since I don't, I'll just guess ! It's much easier than math. Have you seen the lights used on Movie sets? They generally have a rectangular reflector with adjustable flaps. Make one of those. Go to Harbor Freight and get a hand-cranked winch, the hardware store and get some rope, a pulley, some chain, and some screw hooks. Put the screw hook or whatever up in the peak of the GH, put the pulley on the hook, run the rope through the pulley. Mount the winch at a comfortable height, put the rope on the winch and the other end of the rope, attach to the chain on your HPS light. Now, crank the light up and down until you find the right height. As for the second question, you can get a photocell plugin for a few dollars. They're designed to turn on lights after dark. If you could find a really good one it might even have an adjustable setting. I put in a floodlight at our business last year. I climbed down from the ladder, threw the switch and waited for it to get dark. Finally, the light came on ! I was so happy. And then the light went out. I wasn't happy anymore. And then the light came back on ! But this time I was suspicious. I watched it go on and off, on and off, and finally realized: The light went off every time a car drove past the front of our business ! I stood there, thinking furiously. The sensor must be too sensitive, I decided. The headlights of cars were tripping the light sensor to the OFF position. So, I could go buy another sensor. Nope. Didn't want to do that. Can't take it back either, the floodlight had sat in it's box for a year before I got around to mounting it. So instead I climbed up the ladder, stuck a plastic flower pot over the sensor, and lashed it in place with black electrician's tape. Now, the headlights can't trip the sensor. Only true daylight is bright enough to shut the light off. So if you can't get an adjustable sensor, try the flower pot trick.

Amongst my work colleagues, at least, statements like "all generalizations are false" are part of a well-known joke. We say "all generalizations are false... including this one." Since two people (at least) reacted negatively, I probably should have included both the punchline and a smiley for those who don't get my sometimes dry humor. Sorry if it seems like I was flipping anyone off. I tried to show examples of sales tax being due and collected collected when one might think it would not, as well as the other way around .. so I was really only trying to make the point about generalizations being dangerous and often inaccurate. FWIW, I believe that MT and OR are not the only states with no sales tax... I think NH an DE (and AK) similarly have no sales tax. I don't know if local jurisdictions impose a tax or not, nor do I know anything about whether the jurisdictions in any of these 5 states impose a use tax on out-of-state purchases that are brought into the state. Obviously, a person living in these states have a different set of concerns than persons who live in other states. It's also true that some states have (like NY) have what I think they call "safe harbor provisions" on their tax returns. With these, you can voluntarily pay the state essentially an "estimated" use tax based on your AGI. These may not cover everything -- in NY I think it only applies to purchases under $1k. YMMV, of course .. .and I'm not a lawyer, CPA, or employee of the Tax department. The real point I was trying to make is that folks should 'never say never' or 'never say always' when it comes to these kinds of topics, since the laws vary dramatically from state to state. Finally, re: local vs. "internet" purchases -- Weissman is correct that depending on the individual (and the manufacturer), after sales service may or may not be a consideration. The macroeconomic arguments for or against local vs long-distance purchases are interesting. The conclusion is not obvious (to me, anyhow). The impact on the local economy is more obvious. This should be an incentive for "local" vendors to provide well-trained sales folks and competitive pricing.