small help cree xml for my new 75 g tank

[Gamezawy]

i am building a new 75 g tank and i am confused about its lighting

tank dimensions is 40 inch long 24 inch hight 20 inch deep

i want to use CREE XML running at 3 MA so it will be about 10 watts each

i am aiming for hight light plants

leds will be about 2 inchs from the water surface

so how many leds i should use on my tank without lenses as you know that cree XML is 125 degree by default

and how many leds i should use on my tank if i could use 90 degree lenses

[Hoppy]

I suggest 2 rows of LEDs, with the rows about 4-5 inches apart, with the LEDs spaced 4 inches apart in each row. So, about 18 to 20 LEDs total should do it. Use drivers that can be dimmed, so you can adjust to get the light you want. I think at about 2.5 amps you will get around 50 micromols of PAR, which is medium light, if not higher. At 3 amps you should easily have high light. The PAR will drop off some near the front and back of the tank, but not too much. The disadvantage of this will be that the plants will tend to grow towards the light, towards the middle.

If you hang the light about 2 feet above the top of the tank, use 60 degree optics, with the LEDs spaced 3.5 inches apart, you should get about the same PAR, but the plants wont grow towards the center nearly as much. That would mean about 22 total LEDs.

[jcgd]

I have a fixture running 28XML at under 1000mA a total of 40" off the substrate with 40 degree optics over a 72"x24"x22" tank. The leds are spread over a pretty even area of 6"x72". My par at the substrate is about 90 and at the waters surface is about 180umol. The intensity drops minimally at the glass as you move up in height.

No reason at all to run the XML at 3A, because you would would be wasting most of the energy in light spill, or needing the fixture too high to be practical.

I also 24 XPG (60 degree optics) in the same fixture which when running at 1000mA about 28" off the substrate provide more than 50umol at the substrate.

[Gamezawy]

thanks Hoppy thanks jcgd really its cool when someone help you

well here in Egypt i cant find those lenses for the leds and e-Bay dose not deliver to Egypt

that's why i want to use it without lenses

i have some other questions but i wanted to say thanks well brb for now

the main plant i want to have is HC carpet so am i right in choosing XML led and high spec ?

[Gamezawy]

but hoppy i have tryed your PAR_Calculator 5 and i have inserted your suggestion in it but it gave me only 20 PAR value



so how this is going to work as high light ?

mybe there is somthing i miss so please advise

[Hoppy]

I have to use 72 degrees as the optic angle for XM-L LEDs for that calculator to give a number that matches what I have measured. Here is what it gives:

[Gamezawy]

yes but XM-L LEDs angle without optics are 125 degree and its hard to me to get thos optics

and with 125 degree on your PAR_Calculator still gives only 20 par

sorry if i misunderstand what you are trying to say to me

[Hoppy]

Originally Posted by Gamezawy

yes but XM-L LEDs angle without optics are 125 degree and its hard to me to get thos optics

and with 125 degree on your PAR_Calculator still gives only 20 par

sorry if i misunderstand what you are trying to say to me

That calculator is based on http://www.plantedtank.net/forums/sh...&postcount=265 Notice the notes under the chart - I had to assign a 72 degree cone angle to the XM-L LEDs to make the data behave. This is for LEDs with no optic attached. It just took that angle to make the data fit with other data. The calculator gives you an approximation of how much PAR you get, not an exact number.