2) normal hps of 250 watt has 33000 lumens. i need 3 vero 29 to reach same brightness. it results into 240 watt (not taking cooler and loss into the account). of cource the spectrum is different. anything else i need to take into account?
The general argument in favor of LED has become based on directionality and it is a huge issue. The question is, how much of the HPS bulb output actually ends up in the canopy? Because it emits in a 360 degree pattern, 70% or more of its light is headed in the wrong direction and needs to be reflected, possibly several times before reaching the canopy. Each time the photon bounces it has a chance of converting into heat. I estimate that this process consumes 25% of the output of the HPS. Then we also have to consider how much is lost in the glass of the HPS hood, especially if the glass smudged, dusty, dirty, smokey etc. The LEDs on the other hand can be kept very close to the canopy to avoid the need for lenses or reflectors and lose maybe 5% to scattering.
Then there is the argument of spectral efficiency, the idea that the more a plant has to adapt to the spectrum it is given, the less efficient photosynthesis will be. HPS does have a lot of green and yellow output when compared against a 3000K LED, so there may be some advantage there for the LEDs.
Then we have actual efficiency to consider. With a brand new bulb, 600W HPS is about 35% efficient at converting electricity into visible light(150lm/W) (thank you
@Richelsdorfite for
confirming this). The 250 HPS claims 132lm/W so we could say it starts off at 31% efficient. The build you cited, (3) Vero29s at 240W (2.1A) is about 32% efficient, so that should significantly outyield your HPS in terms of grams/dissipation W, mostly because of directionality. When DIYers ask for advice I recommend the CXA3070 AB at 1.4A which dissipates 52W at 42% efficient. That secures our advantage over HPS and is a knockout in the LED vs HPS argument IMO. That said, some DIY flowering lamps are up to 49% efficient and vegging lamps up to 60% so you can imagine the potential in the future.
And finally we have to consider lumen depreciation. If you are like me then you hate to throw away a working light bulb. So I would let my HPS bulbs age for as long as they wanted and eventually burn out before I would replace them, sometimes 24 months! The bulbs I was using were very cheap and it seemed like they were only performing optimally for one cycle and then yields would severely decline on me. For the record that was very counterproductive on my part.
brand new (600W) HPS bulbs start off at 36% efficient and output drops fast. After 6 months of 12/12 it is down to 31.5%. After 12 months it would be down to 29.5% efficient. Metal Halides have it even worse. That is very encouraging for the economics of LED.
So when you add it all up, what ends up happening is you need many more HPS Watts to get the same job done as high efficiency LED. This results in a potentially very large decrease in canopy heat, which is a huge bonus for electrical usage, stealth and bud quality.
. Thermal plaster/adhesive works but can be a bitch to pry off if you want to reuse your heatsinks.
I'm going to put it in a nice box, with a fan on top if it's feasible.
