# Watts per litre with LEDs



## Justal

Working out watts per gallon / litre is easy with standard T5's etc as the quoted watts on the tubes all seem fairly comparable - I realise that depth of water, distance of lights from the water surface, presence of condensation lids etc etc will make a difference, but if I have 50 watts of light over a 100 litre tank I can consider that as 1 watt for every 2 litres, or 0.5 watts/litre

How do I work out a similar Watts per litre for LEDs though? They operate at a much lower power consumption so presumably you need fewer watts per litre with LEDs, but just how many watts / litre do you need when using LED lights? Is there a comparison table somewhere comparing watts/litre for T5's vs Watts/litre with LEDS?

Thanks,
Al.


----------



## ian_m

1. Most of the respectable LED manufactures quote PAR. So buy one, job done. So 80 PAR and above is high-light, high tech. Done
2. Find the number of lumens for your LED fixture. All respectable manufactures quote this as well.
3. Find the equivalent lumens for a T5 tube, eg on Arcadia for instance. http://www.arcadia-aquatic.com/freshwater-lamp-t8-t5/
4. This will give you your rough T5 wattage (or T5 is roughly 85lm/watt, so divide your lumens by 85 to get T5 watts).
5. Convert tank size to US galls (x 0.26) to work out you T5 watts/gallon.


----------



## Justal

Hmmm, thanks.
Previously my 125 litre (32 gal) tank has had 3x 25 watt tubes... So 2.34 w/gal which sounds about right to me and has worked well for the past 10 years.
Was the 85 lumens per watt for T5s a fairly accurate average or just a made up figure? If accurate that would work out to be 6375 lumens for that tank.

My new 190 lite (50 gal) tank comes with 44w LEDs with 3824 lumens. Using the lumens/85  calculation that works out to be only equivalent to 44 watts or 1.13 w/ gal which doesn't sound like enough. 

Am I likely to need to buy another LED light for my new tank?

Al.


----------



## ian_m

Justal said:


> Was the 85 lumens per watt for T5s a fairly accurate average or just a made up figure


T5HO is 85lm/W. eg Arcadia T5 Freshwater is 3250lm for 39W -> 83lm/w. However a none HO T5 I find @ 1200lm for 39W -> 30lm/w. So need to determine if you had/have T5 HO tubes, some of the special "plant grow" tubes are in this category.

You state 25W, which is not a standard T5 wattage, so I assume you have the less efficient T8 tubes (which are available 25W) these are typically only 1800lm -> 70lm/w (actually not that less efficient).

Oh this is with reflectors as well.


----------



## GreenNeedle

Your 44W will be fine as long as it is a good unit with good LEDs and good lenses   I would equate Quality Leds at circa 1.25 to 1.5 x T5, more for T5HO.  So 1WPG of LED = 1.25 to 1.5WPG of T5.  And maybe much closer to the 1.5 of T5HO as T5HO is not as efficient per watt as T5NO.

Are the Arcadia Freshwater T5(NO) or T5HO?

My LED setup using cheap Chinese Luxeon knock offs (so way out of date and no way near as good as current Cree/Bridgelux etc) works out at 52.5W over a 144 litre.  So it is quite comparable to yours although mine will probably be laid out in a more even spread than a retail unit.  I would consider mine in the medium to high light region and only run it on full for 6 hours.


----------



## Justal

Aha... I think you've hit the nail on the head there - They must be the (slightly) less efficient T8's - They are quite old which means I've been using around 5250 lumens - although probably less than that lately seeing as the tubes themselves are quite old.

Your comments are also reassuring SuperColey... Thanks. if the 1.25 - 1.5 times the wattage of T5's for LED is about right, then as I've been using T8's I assume I can use at least the higher end of this. So 44W (LED) x 1.5 = 66W (T8 equivalent). Still less than I have on my current tank, but judging by what you've been using still sufficient. I hopefully won't have to buy any more lights.

The ones I have are these: http://www.aquatlantis.com/index.php?id=626&tbl=registos&crct=1 - Which are hopefully considered as a 'good unit with good LEDs and good lenses'?

Hoping to start work on the set up at the weekend.
Thanks again,
Al.


----------



## ian_m

Yes these are quite good. Not using the most efficient LEDs (ie any Cree above 1W) but they quote lumens and more interestingly T5 and T8 equivalent so you can work out if they are going to be brighter than your existing lights. Their LED wattage to T5 is about 1:1 as not using most efficient LEDs but that really doesn't matter in this case as just plug into T5/T8 light fitting job done.

Just watch out for algae if you are moving from ye olde T8s as the light increase to these LEDs or T5 is quite a jump.


----------



## foxfish

Hi justal, you said you have been having success  with your T8 lighting for ten years & you also said the "slightly less efficient T8's" well I can tell you that from a planted tank perspective (as Ian says) T5s are quite a big jump up!
Beware the dreaded algae - the good thing about many LED units is that they can be adjusted for intensity.


----------



## ian_m

Changing from T8 to T5, as stated is a big jump and yes algae started to appear, so rotated the T5 reflectors around to lower tank light level for a month or two until I got algae under control. Appeared on my Anubias, rocks and front glass. All sorted now, full T5 + reflectors 6 hours a day and algae free.


----------



## Justal

OK, that all sounds promising then... If its a fairly big jump from 75 Watts of T8 to these 44W LEDs then that should be good as they won't be replacing the T8's but will be going over a new tank which is  a little bigger and most importantly in this respect a fair bit deeper than the ones I have the T8's on. Hopefully with all that taken into account things will be comparable, or maybe even slighter brighter lighting in the new tank.

I'm not sure if the LED lights allow me to adjust the intensity, but maybe their LED control box (http://www.aquatlantis.com/index.php?id=329&tbl=registos&crct=1) will allow me to do so - I was thinking of getting one anyway.

I'm hoping to start work on the new tank at the weekend and this will be my first properly aquascaped tank so I'm just trying to get my head around how all of the new, up to date equipment will compare to the dated equipment I've used in the past. I haven't decided whether or not to inject CO2 yet. I might try it without at first to see how I get on and then add it later if needs be. I guess that will depend largely on the types of plants I want to grow.

Baby steps to start with so the weekend will be spent constructing the cabinet, positioning the tank and other hardware so that I can make everything fit in nice and neatly and then maybe making a start on the hardscape... I need to go out into the hills to collect some rocks for that as well though so there won't be any rush

Thanks for the help.
Al.


----------



## Michal550

Justal said:


> Working out watts per gallon / litre is easy with standard T5's etc as the quoted watts on the tubes all seem fairly comparable - I realise that depth of water, distance of lights from the water surface, presence of condensation lids etc etc will make a difference, but if I have 50 watts of light over a 100 litre tank I can consider that as 1 watt for every 2 litres, or 0.5 watts/litre
> 
> How do I work out a similar Watts per litre for LEDs though? They operate at a much lower power consumption so presumably you need fewer watts per litre with LEDs, but just how many watts / litre do you need when using LED lights? Is there a comparison table somewhere comparing watts/litre for T5's vs Watts/litre with LEDS?
> 
> Thanks,
> Al.


http://tropica.com/en/guide/make-your-aquarium-a-success/light/


----------



## GreenNeedle

I have my doubts about those tube replacement LEDs.  I don't really get why (other than a sales point) they would get LEDs and then try and use them like a flourescent when the strength of LED is being able to spread all the light out rather than confine it to a small linear area but that is pure speculation.  I have never used them nor seen them in action.  I just question the logic of not using a strength of LED simply to make them look like something people are familiar with 

On the tubes T8 isn't that far behind T5 at all.  It is slightly behind but not by much.  The thing that puts them behind is that most T8s are running off magnetic ballasts whereas most T5s and all T5HO run off electronic ballast.  If you ran T8 off an electronic ballast the difference would be much more slight W for W.  Another factor is that the reflectors made for T5 are much better than T8 ones so that gains as well.  There is also the issue that many manufacturers used underpowered ballasts in their T8 stock lights.  i.e. a Fluval I had was using a 2x15W magnetic ballast to power 2x18W tubes therefore it wasn't just the ballast that was inefficient, it was only pushing 30W and not the 36W advertised 

So in reality it is the setup that T5s tend to be used in that is better than the setups that T8s tend to be used in.

T5*(NO)* is the most efficient and best W for W, however T5*HO *means you can use less tubes and they will reach a bit further due to their intensity.

I would have to question their findings of MH being the best per watt.  The tests I saw years ago circa 2006 were that MH was behind Flourescent and way way behind LED in terms of PAR.  Even bigger difference in PUR.  This was a 75W LED unit compared to a 250W MH.  In this test the 75W LED nearly matches the 250W MH for PAR.  *It outperforms it for PUR even though it is less than a third of the wattage.*:

http://www.advancedaquarist.com/2006/8/review2


----------

