Hello Heavy Consumer:
Thanks for the reply - those are good questions. Given the # of actual LEDs used and the coverage area, a better comparison to the Plant Photonics 280 watt module (156 Osram OSL SSL80 LEDs) would be the Zelion HL 3x2 (
http://www.dlplampsource.com/zelion-hl-3x2.html). This unit is rated at 150 watts (126 Osram Oslon SSL80 LEDs) and has a coverage area of 36x24". It is a better priced solution than purchasing (2) of the 2x2 units. The 3x2 is priced at $1389. A (very) rough conversion of 799 GBP to USD for the plant Photonics module puts it at around $1200 USD.
Speaking to the Zelion HL 3x2 fixture, it is IP65 rated and passively cooled (no fans). To the individual hobbyist this may not be that important, however it is a testament to the build quality and less moving parts means less hassle with fan bearings wearing out or failing. Also the official UL certification and IP65 rating are very important distinctions for commercial installations in order to pass building codes for use in a damp environment. The Zelion HL fixtures optics were custom developed for even PAR coverage over the entire growing area - the center point measurement of 1100+ micromol/m2s2 is guaranteed to be no less than 1/5 that in the corners (the furthest point from the center). This even distribution ensures the maximum amount of energy is being placed in the entire area without hot/cold spots. Wattage is important in measuring the power consumption of these units (determining overall efficiency of the unit as well as to determine how hard the LEDs are being driven), however to get a good understanding of comparing the "light power output" of one LED fixture to another is the measurement of PAR, and how even and strong that measurement is over the coverage area advertised. In the case of the Zelion, the LEDs are driven at roughly 40% power, which is low. This is done to make the units more efficient in order to save on energy costs and increase the longevity of the diodes, indeed why the Zelion carries a lifetime rating of 100,000 hours at L70. Of note, the L70 means the LEDs are putting out 70% of the original power (this is an industry standard).
Being involved in the development of this fixture, I can attest to the incredible amount of engineering that has gone into the development of the fixture. It is exceptionally engineered (as one would expect from Osram, and given the fixtures pricepoints) from the custom power supplies, to the custom optics to the hand assembled final product - we have studied all of the fixtures on the market and the build quality of the Zelion is unparalleled. I understand that to some this may not be a selling point for some customers - and perhaps it is not - but it does speak to the quality of material and level of craftsmanship. Don't get me wrong - we aren't talking about fancy exotic sports cars here - I understand that it is still a light fixture. The Zelion is a premium priced product - of that there is no question. It is more expensive than the others. It also performs better - more PAR/watt - than many other grow lights and is designed to do so for a longer period of time, using less power and with less opportunity for failure (again, no moving parts). It's also silent and puts out little/no radiant heat - an issue with other passively cooled fixtures, since these are designed to operate close to the canopy.
These are available in four different "sizes" or coverage areas (1x1, 2x1, 2x2 and 3x2'). In some cases of smaller, hobbyist size configurations, a combination of HPS and/or MH and LED has been proven to be good, as is the simple addition of white LEDs in the form of PAR reflector LED bulbs or larger white LED DIY-type configurations. In addition to operating independently, they make a good complementary light to your existing setup. For those new to LED grow lights and wanting to experiment, or are simply on the fence, the less expensive smaller units offer an opportunity to enter the LED market at a more price conscious level without having to settle for a low quality LED grow light.
I hope this helps - if I can contribute any additional information I am happy to do so. Thanks again for the opportunity.
Regards
Dan
But I don't know which of this lights is better and worth the price. That's why I need your help guys 
