# How much Wattage LED required for a planted tank?



## shellydsilva

Hi,

How much wattage of LED do I need for my 35 gallon planted tank?

Generally when we go for T5/T8/PLL/MH, we take the rule of 2.5 - 3 WPG. But when it comes to LED, how do I determine on how much wattage of LED is required?

Is there any calculation to determine the LED wattage required?

Regards'

Shelly D'silva


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## Hoppy

You can't select the right amount of light by looking at the wattage, no matter what type of lighting it is. If the tank is a high tank, it needs a lot more light than if is is a low one. And, the different types of lighting, T5, T5HO, T8, MH, LED, have widely varying brightness per watt. For LEDs read http://www.plantedtank.net/forums/diy/84212-designing-building-led-fixture-22.html#post1102937 and http://www.plantedtank.net/forums/lighting/108678-cheap-led-light.html#post1086506

Remember, light isn't like a chemical or a fertilizer. It doesn't mix with the water in the tank. It just shines on whatever is in the tank. So, the important factors in determining how much light you have, in addition to the type of lighting, are the distance from the light to the substrate, the length of the tank, and the distance from front to back of the tank. The number of gallons of water in the tank has nothing to do with how much wattage of light bulbs you need.


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## shellydsilva

Hi Hoppy,

Thank you very much for giving me the info. But this seems to be a rocket science for me..Yet, I will take time to read and understand it before I start this LED project for my 35 Gallon (30" length x15" width x 18" height) and 62 Gallon (36" length x20" width x 20" height) tank..

Can you please explain in laymens language on how to calculate the LED watts required? Sorry If I am asking it too early before reading the links you have given me. 

FYI.. I have seen this LED's in the local electronic shops in my city.

Edison-opto
1W and 3W are avilable in the shop. Cool light and Neutral White.

Regards'
Shelly D'silva


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## Hoppy

If you want medium or higher light you could use a grid of 3 watt LEDs spaced 3 inches apart in both directions, about 36 for the smaller tank and 66 for the larger tank. That should give you about 50 to 100 micromols of PAR, depending on whether you use less than 400 mA current or 800 mA, which is low medium to high light over the entire substrate, and very uniform.

I don't know any simple way to calculate how many LEDs you need, other than using the graphs I posted, which give you the grid spacing of the LEDs versus the distance from the LEDs. You don't need the LED grid to extend all the way to the ends and sides of the tank, but they should extend to at least 3 inches from each end/side.


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## shellydsilva

Hi,

Thanks for the Info.

If I put 60 Deg optic's can I increase the LED gaps from 3" to 4"?

Now I will plan for the power supply and driver. Thinking of going for DIY driver circuit and power supply.

Regards'

Shelly D'silva


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## shellydsilva

Hi Hoppy,

Is this basic design of the LED power supply/driver is correct?









Regards'

Shelly


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## shellydsilva

Hi Hoppy,

Is this basic design of the LED power supply/driver is correct?









Regards'

Shelly


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## csmith

http://www.barrreport.com/showthread.php/7486-DIY-LED-Luminare-MkII


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## DarkCobra

The 60 degree optics will work; but of course you'll have less light, because you have less LEDs. And you lose a little more, because the greater the angle light strikes water at, the more reflects off.

The basic schematic looks fine. 48VDC is enough to hurt you under the right circumstances, so be careful.

One extra bit of advice. Make very sure you're going to be happy with the color and spectrum of the LEDs for a long time, before you embark on the full project. There is no adjusting color by swapping out bulbs with LED fixtures! You could add extra colored LEDs to tweak color balance at a later date, but this can result in multicolor shadows, which may be undesirable.


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## shellydsilva

Hi,

Thanks for the info. 

As you have mentioned 48Volts DC is dangerous enough for a person to get hurt , I am planning to use 12Volts. If I am using 12Volts, then how do I wire the LED's?

How many LED's can I connect in series? 4LED's or can I connect more?
Also to drive 36 LED's, will one 12Volts power supply will be sufficient?

In addition, can I use the computer SMPS to power the LED's. Specification of a normal SMPS says, 12V and 12A current. Will I be able to use this smps as LED supply?

Regards'

Shelly D'silva


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## DarkCobra

Shelly,

My warning was not meant to discourage you, only to make sure you were aware that 48VDC circuits require a little care and respect. Most times when working with DC it's at 12V or lower, and so we get accustomed to the idea that DC is entirely harmless; which tends to foster bad habits that might earn you a painful jolt when working with 48V. 

If you have access to a 48V power supply and 48V capable constant-current drivers, designing LED fixtures as large as these can be simplified.

Consider LEDs that have an average forward voltage drop of 4.0V (to make an example, as I'm not sure of the specs of the actual LEDs you're considering). The driver will also have a voltage drop, and the LEDs' forward voltage drop vary slightly, so let's assume we need an additional 1V headroom:

(48 - 1) / 4.0 = 11.6 (11 LEDs per driver)
(12 - 1) / 4.0 = 2.75 (2 LEDs per driver)

You can see that you'll need 5.5x as many 12V drivers to drive a given number of LEDs, rather than the expected 4x. I deliberately picked a 4.0V LED to demonstrate a worst-case scenaro, here's the same example with 3.6V LEDs:

(48 - 1) / 3.6 = 13.05 (13 LEDs per driver)
(12 - 1) / 3.6 = 3.05 (3 LEDs per driver)

Which is not so bad. It all depends on specifics. If you can get 4x 12V drivers for less money than a single 48V driver, and don't mind having more drivers, this might even work out better. And then of course, you could also use a computer SMPS or other common 12V power supply.


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## Hoppy

shellydsilva said:


> Hi,
> 
> Thanks for the Info.
> 
> If I put 60 Deg optic's can I increase the LED gaps from 3" to 4"?
> 
> Now I will plan for the power supply and driver. Thinking of going for DIY driver circuit and power supply.
> 
> Regards'
> 
> Shelly D'silva


No, adding auxiliary lenses to LEDs doesn't help at all. It just reduces the number of LEDs contributing light to any give spot in the tank, thus causing more "spotlight" effect to be noticeable.


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## Hoppy

12 VDC power adapters are very easy to find, and they are available with a capacity of 4 amps, for sure, and maybe more. I think that is a very good choice for voltage. 12 volts will drive 3 of those 3 watt LEDs in series, and for 800 mA current per LED, you could run about 4 series strings in parallel per power adapter. So, you just need to find or make 800 mA constant current drivers that can handle 12 volts. There are a lot more constant current drivers on the market now than there were a couple of years ago.


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## shellydsilva

Hi Hoppy,

Can I then wire the LED's to the 12V SMPS computer supply like this?

The computer SMPS specification shows 12A. So I think then I can use one SMPS supply to drive all the 60 LED's. Am I correct?

Regards'

Shelly D'silva


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## Hoppy

If your power supply can supply 12 amps continuously, without overheating or shutting down, you could supply 48 LEDs, in strings of 3 - 16 strings of 3 LEDs with each string getting 3/4 of an amp. But, when I tried a 48 volt power supply running very close to its rated power, it quickly burned out. Those power supplies are made for a specific task, and rated accordingly, so they may not be good for continuously running at the rated current. In your situation, with 60 LEDs I think I would use two power supplies, each driving half of the LEDs, or find a unit with a higher maximum current rating.

Also, when you put a constant current controller between the output of the power supply and the LEDs, the current through the power supply will not necessarily be the total of the out put currents. It may be lower or higher, depending on the circuit used in the constant currrent driver. Again, it is best not to try to use the full current capability of the supply.


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## DarkCobra

shellydsilva said:


> Can I then wire the LED's to the 12V SMPS computer supply like this?


Remember I mentioned individual LEDs vary slightly in their forward voltage drop? The result is that when you have multiple series strings connected to one driver, the current consumed by each string will be unequal.

Exactly how unequal will vary. In some cases the difference may be too small to have any real effect. Other times, one string will be overdriven enough to shorten its lifetime; and the chances of this happening increase with the number of strings.

Some possible solutions:

1) Put a resistor on each string to equalize currents. Used more commonly with lower power LEDs, as the resistors waste energy, produce heat, and the resistors may drop the voltage available to the LEDs enough that you can't drive as many per string.

2) Drive the LEDs below rated current. This gives you a safety margin, at the cost of reduced light output (unless you add more LEDs).

3) Sort the LEDs into series strings that have matched parameters for each driver. Rather laborious.

Or any combination of the above.

But none of these address one final issue. What if a series string fails electrically open, due to either a LED failure or a wiring/solder break? The other LEDs connected to that driver in your diagram will then be subjected to 33% overcurrent, which may soon lead to their demise as well.

That's why it's better to have a separate constant current driver for each series string.

When it comes to a project that will require as much time and money as a large DIY LED fixture, I value reliability. Getting 5 years out of something that could have lasted 10 is unacceptable to me; so I build it right and built it to last, taking no shortcuts.


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## shellydsilva

Happen to see an LED driver CAT4101. It can drive 6 LED's in series, with input voltage upto 30V. So will be using 24V supply.

Let me know the suggestions.


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## DarkCobra

Looks like a useful driver. A few tips:

* It's a linear driver (functions basically as a self varying resistor), so can produce more heat than a switching driver.
* The amount of heat it produces is Current * (VIn - VOut). As a practical example, if you can connect 6 LEDS maximum at 24V input, and you do so, then (VIn-VOut) will be small and it'll produce relatively little heat. But if you were to connect only one LED at 24V input, (VIn-VOut) would be much larger; and the extra heat the driver produces is about equivalent to the heat the five missing LEDs would have produced, all concentrated on the driver!
* The resistor on RSET pin should be chosen to produce the maximum rated LED current. If you want to dim the LEDs, it should be done by providing a PWM signal on the EN/PWM, as that's more efficient (less heat) than varying the resistor on RSET.
* I don't know about electronics suppliers in India, but www.findchips.com is useful for comparison shopping price and stock on a bunch of (mostly US) suppliers.


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## shellydsilva

I would be connecting 6 LED's in a single driver, so that the heat issue that you have specified can be ruled out. I would be requiring about 54 - 60 LED's. Hence would be using 10 CAT4101 drivers. In future, if I need to add more LED's, then I can add one more CAT driver.

With respect to PWM, I dont plan to DIM the LED's. Hence I would be connecting the PWM pin to Vin (5V), and will get the maximum output power.

For the A rating, I would be using 750 Ohm resistor, which gives an output of 700mA current. I can also use 1470 Ohm resistor to achive 350 mA current. (As per the design in the CAT 4101 datasheet).

Power supply, I might have to use two supply. One supply 24V 12A to drive the LED's and a regulsted 5 V supply to drive the CAT drivers.

[Query] -- If I use only 6 set of CAT drivers, using 24v 12A supply will make any issue?

Also how many CAT drivers, can I drive using the 24v 12A power supply.

I dont know how to calculate the current/voltage parameters correctly!!!

I think I have to go back to school once again to gain the basic knowledge!!!!!!


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## shellydsilva

I did not find the CAT drivers locally in my city. I found it only in one website. I will have to order it on-line.

I happen to find in *mouser*.com. But the shipping charge is more!!!


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## DarkCobra

shellydsilva said:


> [Query] -- If I use only 6 set of CAT drivers, using 24v 12A supply will make any issue?


No issue with a power supply being able to produce more current than needed.



shellydsilva said:


> Also how many CAT drivers, can I drive using the 24v 12A power supply.


The current required from the 24V supply by a driver is equal to the current flowing through the LEDs attached to it. So:

12A / 700ma = 17 drivers
12A / 350ma = 34 drivers

Although I usually like to keep continuous power draw from a supply to at most 80% of its rating, which would be 9.6A in the case of a 12A supply.

Other current required for internal operation of the driver comes from the 5V supply, and is minimal (Figures 4 and 5), only 8ma max per driver.


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## shellydsilva

Here is a schematic diagram...

Ten set of CAT4101 drivers driving totally 60 LED's.

Each set driving 6 LED's.

Now I need to hunt down the 24v 12A power supply in my city.. Will be traveling to the electronics market today to check the power supply.


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## Tonyoon

Hi there I have a 4 feet standard tank and need some help about my lighting for my plant in the tank
the lighting on my tank are 3 x t5 28 watt 6500 k normal buid not a florescent or any build just very simple buld is it enough for my plant ?


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## Kubla

I was surprised to see Hoppy posting, then saw this thread is 8 years old. 


T5's but they're not floursescent? I'm not sure what your question is.


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## jeffkrol

Tonyoon said:


> Hi there I have a 4 feet standard tank and need some help about my lighting for my plant in the tank
> the lighting on my tank are 3 x t5 28 watt 6500 k normal buid not a florescent or any build just very simple build is it enough for my plant ?



Look like a standard 55gal..and you are running 84W of t5's.. good enough for med light 60PAR at subst

rate woudn't be an unreasonable guess..


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