Why high light in nano's?

[Moody]

Just wondering if anyone realy knows why (in general) you can get away with rediculus high light levels in nano's.
I have had experiance of this, my pico 8lt planted has 19WPG with presurised Co2 and did realy well, my best yet.

What hapens to the WPG rule when looking at pico/nano aquariums? Why does it work?

Cheers,
Graeme.

 

[tropicalfish]

The Watts per gallon (WPG) rule usually works, but begins to stop working in smaller and much larger tanks. Let's say I get a 1 gallon tank, and I put a 5 watt bulb on it. Well, I have 5 watts per gallon, why can't it be used? Reason: 5 watts is dimmer than you will need to grow plants.

 

[VaughnH]

There is no theorectical reason why watts per gallon is a valid parameter for how much light plants need. It just happens to be an easy number to determine for any given light fixture, and coincidentally, it can be used to approximate how effective a light fixture is. But, obviously, a ten watt light that produces mostly infrared or ultraviolet radiation is not going to be as effective as one that produces a spectrum that mimics a 6000 K black body, and if that light is three feet above the water it isn't as effective as if it is three inches above the water. It just isn't a valid parameter for anything approaching a scientific method. Just be happy it works reasonably well for tanks in the 20-100 gallon range.

 

[Dave Spencer]

Have a butcher`s at this Graeme. Personally, i think the calculator at the bottom overestimates the light levels required.

Lighting in Amano Aquaria

Dave.

 

[JamesC]

I think what Graeme is trying to understand is why the rule breaks down for smaller tanks. My first thought was that possibly the lumen to wattage ratio for fluorescent bulbs wasn't linear but actually looking at some figures for different bulb sizes this isn't the case, so rules out that theory.

I then thought about surface area and this is where I think the watt per gallon rule goes wrong. If you have a 5 gallon tank and a 50 gallon tank this equates to a volume difference of 10 fold but the surface area difference will be a lot less, possibly about a quarter depending on tank dimensions. Now doing some quick figures in my head a 50 gallon would require about four times the amount of light than a 5 gallon to achieve the same level of 'brightness'.

So calculating watts against surface area may give a more accurate representation because changing the depth of a tank greatly affects the watt per gallon figure but not the watt per surface area figure. To my way of thinking it's the amount of light on top of the tank that matters as the depth (within reason) doesn't make too much of a difference to the lighting levels

If memory serves me correctly then this has all been gone into many times before on different forums and the conclusion always seem to be that for simplicity sake it is best to stick with watts per gallon.

Hope that makes some sort of sense
James

 

[Tom Barr]

Simply put: smaller bulbs suck.

The 13w PC lights stink ve an 18 w or a 40 watt relative to distance and micromols of light put put relative to watts.

I have 26w of 2x13 w PC lights putting out only 80 micromols at 4" and the an 18 w lamp, less watts mind, still a PC and still 4" and it puts out about 180 micromols.
The 40 watt on a tank 2x the size puts out 250.

So.............the ability for a dinky little light to produce the same amount of light per watt goes down as you reduce tank size.

Regards,
Tom Barr

 

[Moody]

So there is no real reason, it just so happens it works.
Is there a test to be done here?
There was something I read about LUX per square inch. Below 20Gal is this a much better aproach to lighting a nano?

Sould it not be more, watts to surfice area AND depth? If so, how would you figure that out.

Im just realy exploring why, I know it works, and i know how to implement it.

Thanks for the link Dave, found that a while back, still doesnt answer anything.

Cheers,
Graeme.

 

[Anti-Pjerrot]

Sould it not be more, watts to surfice area AND depth? If so, how would you figure that out

Thats volume!

 

[Moody]

Doh, your right!!

So there you have it. Back to the begining. How do we get the right light for nano's and pico's. Sould there be a WPG for tanks from 10gal-200gal, and then a second set for 0-10gal and 200-........gal?

Why would the WPG rule also not work for extra large tanks, whats going on with light in small and large volumes?

Graeme.

 

[Tom Barr]

Well, the smaller bulbs have less area, thus are more light a point source, they are cheap, wimpy and have namely poor light from the electrical nodes which on a small short tube means less for the rest of the bulb.

They also have junkier reflectors as a rule.

The scale for micromols per watt is not linear.
Other issues such as finding a small enough light for a nano is also a reason.
Water mixing is also easier in a nano.
On a large tank with many bulbs, you have many different angles that light can strike the leaf, but in a very small tank close to the surface, all you have is one direction and little diffusion.

Rather than guessing the light intensity, I just use a light meter that measures micromols, they cost 249$ now for the Apogee, much less than the old days of 600-1200$ for the licor meters.

Regards,
Tom Barr

 

[defdac]

It's all about the area.

See the applet: http://standards.nctm.org/document/eexamples/chap6/6.3/part2.htm

So when you change the volume and the wattage down to half, you've not changed the area nearly as much - thereby less wattage and intensity per area unit.

 

[Moody]

Cheers for all that, but you dont know how confusing it can be to read all that when your NOT an academic science nut ,like your selfs.

So it realy comes down to practical gear for the job?
A small bulb/tube doesnt cover as much of the tanks water surfice area?
So its efficiancy rather than watts used, its how they are used thats more important?

Its all abit vauge,

So would say 12 ,1 Watt tubes spaning over a 30cm cube be more efficiant than one 24Watt over the same tank in the centre with a reflector? Or even 6, 1 Watt Tubes over a 30cm cube against one 24 Watt in a central position.

I fear this is making me look realy thick, im just trying to understand how it all works.

Am i making scence?


Cheers,
Graeme.

 

[defdac]

Cheers for all that, but you dont know how confusing it can be to read all that when your NOT an academic science nut ,like your selfs.

When you change the volume you change the area less. So the one watt per 2 gallons will not have to cover as much area as the half watt per 1 gallon - You've cut the volume and wattage down to half - but not the area.

It's a bit counter intuitive.

Those making fancy packaging is very interested in this since they want the package to look really big (big area) but contain as little as possible.

A small bulb/tube doesnt cover as much of the tanks water surfice area?

With the correct reflector you can have whatever bulb size you want shoot down all it's light into the tank without spilling any wattage.

That said, 2 completely reflected wattage over 1 gallon will shoot more light per area unit than 1 completely reflected wattage over 1/2 gallon.

Rather counter intuitive - A big tank will need less watt per gallon to achieve the same intensity per surface unit as a small tank. The reason is that the area change more than the volume.

So its efficiancy rather than watts used, its how they are used thats more important?

Yes and no.

2 unreflected watt per gallon in a small aquarium is much less than 2 reflected watts per gallon in a big aquarium.

So would say 12 ,1 Watt tubes spaning over a 30cm cube be more efficiant than one 24Watt over the same tank in the centre with a reflector? Or even 6, 1 Watt Tubes over a 30cm cube against one 24 Watt in a central position.

No. The tank size is the same and it's easy to make the 24 watts spread out evenly with a reflector.

12 watts over a 30cm cube will always be less than 24 watts over a 30 cm cube.

Small lamps is also generally less efficient making light out of electricity - 24 1 watt lamps will have less light output than a single 24 watt lamp because of this. It's not overly important though, the difference is managable.

 

[Moody]

Thanks for that, i think im getting it now

So there is an inportant link with volume and surfice area.

Im thinking about 2 cubes i have, one is a 20cm cube and the other is a 30cm cube. One ( 2ocm) holds 8 lts the other holds 27. The volume is a big differance but the sufice area that the light is hiting is not such a big differance.

So i think ive worked this out right, but please correct me if ime wrong, havnt done real math since school.

The sufice area of the 20cm cube is 40cm square. The volume is 8 lts.
The sufice area of the 30cm cube is 90cm sqoare. The volume is 27 lts.

Differance in area is 50cm, in volume is 19lts.

on the 20cm there is 19WPG.
on the 30cm there is 3.4WPG.

Hmm, not sure how to work this one out.

Any theory.

 

[defdac]

(Just to see if I get your data right:
19 wpg = 5 wpl over 8 lts => 40 watts over the 20 cm cube.
3.4 wpg = 0,89 wpl over 27 lts => 24 watts over the 30 cm cube. )

The sufice area of the 20cm cube is 40cm square. The volume is 8 lts.
The sufice area of the 30cm cube is 90cm sqoare. The volume is 27 lts.

20cm*20cm= 400 cm2 =4 dm2 => 10 watts per dm2
30cm*30cm= 900 cm2 =9 dm2 => 2,6 watts per dm2

So you have 5,6 times more watts per volume over the 20 cm cube but only 3,8 times more watt per area.

 

[defdac]

On top of that small aquariums is often much more crowded with fine leaved dense plants with alot of self shading and less open free space which also tends to push light requirements up a bit in small tanks.

 

[Tom Barr]

This is sort of like the issue with explaining the water change 50% weekly and dosing does not build up to infinity, initially it may seem counterintutive, but it's not, the area, which is what we use, not volume, to measure light with does not change/scale up the same.

Overall, nanos and smaller tanks are not as efficient.
You get a lot more for your $, design and light on a larger tank.

Regards,
Tom Barr

 

[Moody]

(Just to see if I get your data right:
19 wpg = 5 wpl over 8 lts => 40 watts over the 20 cm cube.
3.4 wpg = 0,89 wpl over 27 lts => 24 watts over the 30 cm cube. )


20cm*20cm= 400 cm2 =4 dm2 => 10 watts per dm2
30cm*30cm= 900 cm2 =9 dm2 => 2,6 watts per dm2

So you have 5,6 times more watts per volume over the 20 cm cube but only 3,8 times more watt per area.

Cheers, could you explain dm2 please?

The 20cm cube has a 20W hallogen over it, so your calculations are over estimated.I think.

When you are talking per area, are you talking surfice ie ( at the water surfice) ? or something els?

cheers.

 

[defdac]

dm2 is square decimeter. One cubic decimeter is one liter for example. I used it instead of cm2 to get higher values.

When you are talking per area, are you talking surfice ie ( at the water surfice) ? or something els?

Usually the bottom area.

 

[Moody]

Cheers,

This thread isn't very conclusive is it?

So the only real conclusion is that in very small tanks, the reason for the higher light demand is due to poor efficincy light for the tiny area that it is trying to cover.
And for large aquariums, its a case of stronger light to get through the depth and cut through shadows that plants and water may create.

Where there could be a calculation that works I dont know, maybe the one on the " lighting an Amano Aquarium " that Dave posted up?

Are we happy with that, is this all we need to discuss?

Cheers,
Graeme.