I will do my best to answer these questions as no one has answered them yet.
1) There is a learning curve, and for the most part the addition of a small full spectrum lamp (ex. 2700k, 5600k, 6500k CFLs) will aid in yields by properly regulating hormones. If you look at photosynthetically available radiation, and compare it to the human diet things become much more clear. Say you are working out a lot, in order to grow muscles you need the right hormonal releases from proteins and ample stress, round light does this by replicating the "wholeness" of the sun, allowing hormones to be released at a better rate. Chlorophyll reflects the middle of the spectrum *green light* and so it's use and production can be compared to carbohydrates, when you stimulate chlorophyll, use blue and red light, or eat a bunch of bread, you will release the energy the plant needs, but without carotene (which reflects orange light and absorbs other spectrum) or vegetables, or yellow green and teal light, you would eventually succumb to diseases and loss of vigor. You wouldn't be able to properly regulate your metabolism and hormonal responses. Proteins don't actually directly build muscles, all they allow is for you to build muscles by releasing hormones which will tell your cells to convert chemical energy and expand their cell walls to protect themselves from additional stimulation, creating more proteins, but that doesn't mean you eat beef and the beef muscle directly becomes your muscle. I tend to think of round light as this protein, with HPS you are feeding a body builder a diet of pure protein with a side salad and a slice of orange, not exactly the right diet for health but a big dumb pile of muscle will find it appetizing. With LED's you more often than not are feeding a body builder only carbohydrates and a few vegetables with a slice of beef, so you aren't going to get bulky, but you will be very healthy and you will live well but you don't have that hormonal response that is necessary to build protein from chemical energy. Simply speaking you can cheaply feed your self carbohydrates by using leds, and give yourself the right amount of protein and veggies by combining it with a small cfl bulb (50 watts of 2700,5600,6500k for every 300 watts of led). You can use less total watts to produce the energy and hormones you need. So for your original question, fair, they work fairly well as flowering lights depending on the brand. More orange yellow and green are needed in led lights but they should be supplied by round Kelvin light not nanometer specific lights. For the watts they use they work amazingly.
2) At least 600 watts of led should be used to replace a 1000watt HID lamp. Conclusively led's have been proven to veg about 40% better (growth per watt per day) than metal halide or HPS. If I were you I would get a two induction lights to replace the "suns" in your rooms. With Induction lighting you are saving watts (7% lumen per watt increase) and letting the plants use the less known photosynthetic chemicals; carotene, xanthophyll, andanthocyanins. By combining 400 watts of led with a 200 watt induction lamp, blackstar lights could be used to far exceed a 1000watt HPS in flowering. The proof is in the pudding check out TGA Subcool Agent Orange & G13 Purple Haze, Psytranceorgy is using 266 watts of blackstar led 136 watts of 2700k CFL, he yields 8.3 ounces of perfectly trimmed bud. He's > .57 grams per watt which is about average for an HID light. But his room is a 2x4x5.5 meaning it would be a well below average is size of grow. LEDs allow for more plants in the space, it's not just about the full spectrum it's also about internodal spacing and density!
3) With all lights the ideal is as close as possible. This is a very ugly subject for LEDs in my opinion. In the last year LEDs have been attempting to scale up and replace HID lights. Manufacturers are ramping up the wattage of the individual diodes to 3w to 5w. This is seen by many as a good thing but I'm a bit more skeptical. LED's first hit the market as a light that you could put right on top of your plants, but now they can't be that close because the intensity of the nanometer specific light will literally burn the chlorophyll away. So we have sacrificed watts by adding more and we sacrifice their use as supplemental lights by increasing the intensity. With that said they are normally kept at least 12" away in modern units, with some of the units that are designed for green houses (Spectra, Lumigrow, etc...) needing to be as far as 3' away which ruins the efficiency of a micro grow unless you can properly scale it up 400 watts of LED will have the same footprint as a 600 watt HPS, the light will not be quite as lumen intense at the source but the degradation per foot is usually about 10-15% less than HIDs within the first 3 ft, after that they simply degrade by half per foot as all photons start to act similarly to each other as they loose energy.
4) To replace a 1000 watt HID you should also take into account all of the venting that you have to do. Normally at least 40 watts of cooling per 1000 watts (if it's winter, lets be honest). 650 watts of could replace all the lighting and would need about half (and this is being generous to HID) the cooling cost. So at least 20 watts per 1000watts of LED. You would still save on money because on average even huge LEDs have minimal heat dissipation. Some LED lights have better internal cooling and will literally not go above 80 degrees no matter what.
If I were in your position I would divide my watts between EFDL or induction lighting and LEDs. Induction lighting is proven to be more energy efficient than HID lumen per watt. This is a proven fact. And the lights last 100,000 hours because there is no filament to burn out. Personally I would buy american made induction lighting if cost is no issue, as there are less defects and better warranties. My ideal ratio in a 3.5'x3.5' sealed room would be a 200 watt 5600k induction light on the ceiling with 4 100 watt custom LED lights running on the walls (slightly angled in for better spread). This would leave me with 50 watts to experiment with before risking destroying plant's chlorophyll. LEDs are new technology, and as far as I know, they aren't going away any time soon. It's best to save the electricity and experiment with what your plants want. Area 51 has customizable LED lights and they aren't that expensive, although they are a new company and they don't have any grows on this site. I am a plant junkie, I come from a farming community of people who vastly underestimate what plants do. They are capable of much, just because one plant doesn't like your LED light does not mean that LED's don't grow plants, we have been growing and breeding plants under HID lights for the last 30 years, it's safe to say that we got them used to that light. There are other websites and companies that will let you build custom led lights, but they are in China, and an American company will get you a better price because they are buying in bulk from china. Currently the only all American made led units are Apache lights and Lumigrow, but both are much too expensive in my opinion. You can always get Blackstar LEDs. They are proven to work. Anyway good luck on your search for new lights. If you make the switch from HID to LED you will notice a large learning curve. A lot of people don't mention the fact that you water about 1/2 to 1/3 as often as you would with HIDs. This means you are using less water and nutrients as well. It's all relative though. LED's are fucking expensive, so if you are going to invest do it for the long haul so you can learn how to use them. Don't just be a little bitch and throw them away when you can't figure them out, could you imagine how long it must of taken them to get people to stop using candles and replace them with incandescent light. "Why use these bulbs? They burn out, they're to bright, and they don't make my house smell nice. In fact who cares about the future of lighting I'm going to go with what works, and candles just work" There are a few analogies to be taken from that, but just know that an LED light is never going to burn your house down. HPS will if they only get the chance. I don't know everything though, make sure to check with other individuals as more knowledge is more accurate knowledge.
Best wishes in your growing endeavors sincerely,
ILovePlants
P.S. Asking questions is the number one way of getting answers. We are all looking for answers, and we should all be asking questions.
