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LED/MH/T5 equivalence - guesswork help needed!

742 Views 3 Replies 3 Participants Last post by  jcgd
Hi all,

I know this is going to be tricky without any PAR info, but I was hoping between us we might come up with a good guess.

I'm looking at changing the lighting on my big tank (90x90cm, 30cm tall) to a custom LED setup.

Currently, it's running off a single 70W MH suspended 60cm above the tank (90cm above the substrate). This is pretty low light - I'd like to bump the brightness up slightly, whilst remaining low tech.

Now the new lighting unit will be using 3w Chinese CREE copies, but I need to decide how many - I'm getting it made by a guy over on another forum, and he generally works in sort of T8/T5 equivalences based on what the customer is looking to grow but is having a hard time calculating how many would be equivalent to a 70w MH at the height mentioned above.

He's proposed something like 4 rows each of 5 x 3w LEDs, but I'd be very grateful if anyone else would weigh in with an opinion here. I'm not expecting any definitive answers, but some sort of general consensus would be nice!

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I don't think you will get enough light with the configuration you mentioned. I think you will need about 4 -5 rows, 6 inches apart, with 9 LEDs per row. The 90 cm front to back depth makes it necessary to have a pretty well spread out light source, especially with only a 30 cm tank height. This would be with the LEDs running at around 400-700 mAmps, depending on how efficient they are.
Thanks for the reply Hoppy. I've got a little more info on the LEDs now, if it makes any difference - they're apparently 110-120 lumens each, with 90 degree optics.

There's also the option to bump them up to 5W or 10W each.

Do you really think it's necessary to go up to ~120w total to match what I'm getting from a 70w MH?
Even if it only takes you 40 watts to get the light you need, it could take more LEDs to get the proper spread and then dim them back to get the intensity you require.
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