everyone: I was under the impression that while LED's, at this point in time, are slightly more efficient than a good HPS system, but the cost savings on electricity wouldn't be hugely notable. The biggest difference is the ballast vs driver component. If you're using a magnetic ballast there is no contest, LED's with their driver consume far less energy. If it's a digital ballast, however, the efficiency increase is less noticeable. Of course, this does not take SPD into account.
lilroach:
1. Depending on cost of electricity, bulbs and -mostly- your HVAC cost, I'd say 2-6 years.
2. Yes. Check out some of ganja's Astir grow threads. He seems to have had a few hydroponic issues, but both grows I've seen have yielded very well for the wattage. I'm sure more could be yielded from his growing space with more light, but still, it's a very efficient system he's got going.
3. Like Beef said, if nothing else, LED's should be known for the compact veg growth that they can provide. One of, if not the, all time vegging champion (although fluroro's are no slouch). Yet, even if you don't want compact plants for some reason, it's very easy to achieve your desired photo morphology by tweaking your wavelength coverage to suit your needs. As you slowly add IR light to your veg spectrum and decrease the Blue output, the more your plants will stretch. LED's give you that power. You can pinpoint the plants gene makeup so as to catalyze a desired phenotypical trait. Narrow band coverage LED's are pretty cool.
4. Competitive to grow? Because lots of business industrial facilities are moving over to LED's due to their increase in efficiency. Neutral White LED's are very luminous and compete at a higher level than traditional lighting. As for growing, radiometrically speaking, LED's aren't as crazy efficient as one might think. It's still slightly better than HPS, but the difference really isn't that huge when comparing to a 600W HPS which tend to be rather efficient already. The difference in efficiency is derived from the cornucopia of options we have over our light quality. We can use less energy, at roughly the same radiometric efficiency, by targeting photosynthesis absorption peaks. As LED's become more efficient, however, we'll be able to throw whatever color photons we want at our plants (even if it's ugly Yellow HPS colored light that we want), achieve any morphology, and not have to worry about efficiency because it's just that far ahead of anything else. So, going back to your original question, where the technology is right now? LED's are already competitive. Where the technology will be in 5 years? I hope it won't even be a competition at that point...
I use LED and still have to actively cool my system otherwise temps get up into the low 100's during the summer. That said, my veg and flower room combined (which includes all lights, the AC unit, exhaust fans, etc.), consumes less energy than a single 1000W HPS w/ digital ballast and a single blower fan on the cool tube. Yes, I was growing in a 3.5' x 3.5' flower room before, and now I'm in a 2' x 2' flower and 1' x 1' veg, but we're not even discussing the rest of the HVAC costs in the HPS room, and the LED rooms could be scaled up with little overall impact on power consumption by adding another ~30W panel or two.
