How many LEDs?

[alvintran]

I'm going to build a DIY LED light for my 29 gallon system with LEDs from Rapidled, and I'm going to go with the ultra premium kit. But I can't figure out how many LEDs to buy, 12 or 24. Since I'm not doing dimmable, it would be best to not overkill amount of light for the system. I've read that others do 24 leds, but they dim it down to 50%. So would I be able to pass by with 12 LEDs on full brightness for a 29g 30" long? I'm planning on keeping softies, and LPS, possibly anemones if possible. Also, do you know how many watts those rapid LEDs have in each led?

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[alvintran]

Anyone?

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[Reefing Madness]

I think the White LEDs are 5w. Go with the 12 LED Retro kit. Using 80 degree optics. That will provide you with plenty of light.

 

[alvintran]

I think the White LEDs are 5w. Go with the 12 LED Retro kit. Using 80 degree optics. That will provide you with plenty of light.

I was thinking the same, but I've seen a lot of people also with 29g tanks using 24 dimmed LEDs, so I don't know which to pick. So would you recommend 12 LEDs nondimmable?
Also, the driver supports up to 14, so I can buy 2 extra LEDs, should I buy 1 more white and 1 blue, or 2 of one kind? Which kind?

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[Dave A]

First, LEDs run at 100% produce a lot of heat and this will significantly reduce their useful life. Turning them down to 70% will give you 80-90% as much light but produce much less heat, allowing the emitters to last several times longer.
Second, even without a dimmer, it's possible to run LEDs at a reduced current level. Simply choose a driver that puts out the amount of power you desire. For example; a string of LEDs that is rated for 1000mA can be powered by a 700mA driver, this would cause the LEDs to operate at 70% current but they would still (probably, depending on the specific LED selected) put out >80% of their maximum light output.
Different LEDs have different current ratings and different Vf, to find wattage, multiply Vf times A (current in amps, 1000mA =1A). A LED with a Vf of 3.1V @ 1500mA is a 4.65w LED. If it is hooked to a ELN 48-60 at 1300 MA it will likely have a Vf of 3.05V for a total of 3.915w, I wouldn't want to run it that high, it wouldn't last very long. My suggestion would be to use at least 24 emitters and choose a driver that runns them at between 60 and 75%. 12 just won't be enough, even at full power. I run 21 emitters on a 20H.
I'll skip the part about optics selection, that is primarily based on mounting height so we don't have the info we need to make a decent suggestion.

 

[alvintran]

First, LEDs run at 100% produce a lot of heat and this will significantly reduce their useful life. Turning them down to 70% will give you 80-90% as much light but produce much less heat, allowing the emitters to last several times longer.
Second, even without a dimmer, it's possible to run LEDs at a reduced current level. Simply choose a driver that puts out the amount of power you desire. For example; a string of LEDs that is rated for 1000mA can be powered by a 700mA driver, this would cause the LEDs to operate at 70% current but they would still (probably, depending on the specific LED selected) put out >80% of their maximum light output.
Different LEDs have different current ratings and different Vf, to find wattage, multiply Vf times A (current in amps, 1000mA =1A). A LED with a Vf of 3.1V @ 1500mA is a 4.65w LED. If it is hooked to a ELN 48-60 at 1300 MA it will likely have a Vf of 3.05V for a total of 3.915w, I wouldn't want to run it that high, it wouldn't last very long. My suggestion would be to use at least 24 emitters and choose a driver that runns them at between 60 and 75%. 12 just won't be enough, even at full power. I run 21 emitters on a 20H.
I'll skip the part about optics selection, that is primarily based on mounting height so we don't have the info we need to make a decent suggestion.

So would you suggest me doing that, or just buy a dimmable kit with a dimmer? Which one is more bang for the buck?

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[Dave A]

A dimmable kit is probably a better idea than using the non dimmable kit. IIRC, it doesn't add much to the price. A well designed non dimmable kit can work well but the dimmers are nice to have to acclimate new corals or adjust the color of the tank.

 

[alvintran]

A dimmable fixture will cost roughly about $50 more, do you think its worth it?

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[Reefing Madness]

, its worth it. This way you are able to tailor your lighting. But again, that 12 led unit is going to be a lot of light, with thise white leds at 5watts. Most prefer more blue thiugh, and thus the dimmers come in handy also. And extend the life of the led.

 

[alvintran]

, its worth it. This way you are able to tailor your lighting. But again, that 12 led unit is going to be a lot of light, with thise white leds at 5watts. Most prefer more blue thiugh, and thus the dimmers come in handy also. And extend the life of the led.

So 12 or 24 LEDs? And also, I get to choose 2 extra LEDs that the driver can handle, which color should I choose?

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[Reefing Madness]

Navy Blue. And yes, I do think the 12 LEDs would be enough. Not many if any at all run 5w LEDs in their system.

 

[alvintran]

Navy Blue. And yes, I do think the 12 LEDs would be enough. Not many if any at all run 5w LEDs in their system.

So should I go with a 12 LEDs fixture, or 24? What corals can you grow under 12 LEDs?

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[Dave A]

The usual rule is "at least one 3 watt LED for every 15 sq. in. of surface." The LEDs available with the kit can run around 4.5w so they are, theoretically, equal to 1 1/2 three watt LEDs. IIRC, a 29 gal is 12x30, or 360 sq. in., so you need at least 24, 3w LEDs or at least 16 4.5w LEDs. I've never used the XP-Gs, but I have used XT-Es and IMHO, they are no better than a 3w emitter. In fact, I will never use an XT-E again, you get just as much light, and better spectrum, from a 3w Philips Luxeon.

 

[alvintran]

The usual rule is "at least one 3 watt LED for every 15 sq. in. of surface." The LEDs available with the kit can run around 4.5w so they are, theoretically, equal to 1 1/2 three watt LEDs. IIRC, a 29 gal is 12x30, or 360 sq. in., so you need at least 24, 3w LEDs or at least 16 4.5w LEDs. I've never used the XP-Gs, but I have used XT-Es and IMHO, they are no better than a 3w emitter. In fact, I will never use an XT-E again, you get just as much light, and better spectrum, from a 3w Philips Luxeon.

Thank you for the math! I guess I'll just bite the bullet and buy the 24 dimmable LED. Hope it turns out well and my big bucks pay off.

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