So it's not watts per sq ft with LED's?

TedeBoy

TedeBoy

Well-Known Member
I'm obviously new to the LED world with that question.
I found a good price on a Mars II 900 ($200) so I bought it and my flowers are doing good under it getting thick now (30"x 30" x 5' grow space - soil).

Now as I explore higher quality Lights like Area 51 I am learning it's not watts at the plug divided by square feet that is as important as light efficiency. Am I correct?
For instance my Mars draws 411w at the plug but I am willing to bet that a Cree light pulling that would kick its butt.

What should I be looking for when I upgrade from my Mars? For instance would 2 Area 51 RW75's give me every bit as good of a harvest at less than half the watts from the wall? I'm looking for low watts and high efficiency.


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TedeBoy

TedeBoy

Well-Known Member
churchhaze said:
Take the watts dissipated by the leds and multiply it by their efficiency, and you will get PAR watts.

A good rule of thumb is to use 12W/sqft PAR for 2-3 foot plants, 14-18W/sqft PAR for taller.
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More noob questions.

What are "watts dissipated by the LED's"? On mine is that 900w?
How do I calculate efficiency? On mine is it 900 divided by 411?
 
C

churchhaze

Well-Known Member
TedeBoy said:
More noob questions.

What are "watts dissipated by the LED's"? On mine is that 900w?
How do I calculate efficiency? On mine is it 900 divided by 411?
Click to expand...
You have to know what efficiency is already.

First of all, 900/411 would make efficiency 219%. (it can't be higher than 100%)

You can calculate the efficiency of lamps if you have the luminous efficacy of radiation (LER) and the luminous efficacy of source. There are some charts where you can find the efficiencies of the various cobs we're using at different currents.

If the Mars draws 411W, that's the power dissipated. 900W is bullshit. Assuming 30% efficiency (estimate.. I'm not sure what efficiency is for the leds in mars), that would make it 123W of PAR output.
 
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TedeBoy

TedeBoy

Well-Known Member
churchhaze said:
You have to know what efficiency is already.

First of all, 900/411 would make efficiency 219%.

You can calculate the efficiency of lamps if you have the luminous efficacy of radiation (LER) and the luminous efficacy of source. There are some charts where you can find the efficiencies of the various cobs we're using at different currents.

If the Mars draws 411W, that's the power dissipated. 900W is bullshit. Assuming 30% efficiency (estimate.. I'm not sure what efficiency is for the leds in mars), that would make it 123W of PAR output.
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Okay thanks.
 
S

smowstack

Active Member
I doubt any hid manufacturer will advertise the PAR of their lights. Comparing led watts to hid watts doesn't get it anymore. Nowadays light is measured in par. But how much PAR you need to do what a 600w hps will do is still being debated.
 
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