Lights requirement... Im confused !!

[melissa1977]

When you calculate the light per gallon factor do you use the dimension of the tank or the volume of water that sits in the tank ?

For example I have a 20 gallons (high) aquarium (2122). I have 4" of gravel in the bottom and I fill it up to 20". That would mean that im losing about 6" in height and that the volume of water in my tank would be about 16 gallons.

I have 2 florescent bulb both 14w (total 28 W) That would give me a factor of 2W/gallons...regarding lights requirement I would have a medium lighted tank.

Am I right ???
8O

 

[julicat]

Perhaps related, perhaps not: also, don't lights light coralife power compacts put out more lumens that standard fl fixtures? This came to mind because I, too, have a twenty gal and use a 28 watt light fixture...but it is a power compact. Does using power compacts change the two w/gallon rule?

Interesting question, melissa1977. I never thought of it. But I also have very deep gravel on half the tank (the planted half).

 

[chasgood]

A 29gal and a 37gal both have the same footprint 312.5. height is the only difference. If you use the same lights on both, the 29gal would be at 1.3 watts per gal and it will be 1.0 watts per gal on the 37gal. They have the same floor space so really plants in both would get the same amount of light.
Is that right?

 

[medge00]

the standard for finding an approximate way to judge light on a planted tank is watts per gallon or wpg. Many of us shoot for anywhere from 1.5 to 2 wpg for a 'low light' tank w/out co2 or 2.5 to 3.5 for a higher light tank with co2 addition. This is just a way to uniformly look at how much light we should put over our tanks. Its not a science. The 'rule' breaks down on tanks below 20 gallons and does not account for tanks over 30" tall.

Melissa, with 28 watts and 16 fluid gallons you'd be at 1.75 wpg. I'd still stick to low light plants, especially if you're not doing additionaly co2. Thats just my suggestion. You may find 'med' light plants work, you may find they don't. Try an easy one and find out!

julicat, to my knowledge, powercompacts don't really change the rule. 28 output watts of flourescent light is 28 watts. Your bulbs are probably smaller and more efficient than standard flourescents, but they're putting out the same number of watts. Lumens, to my understanding, aren't necessarily the best way to measure light for our uses. I could be wrong, but this is how I understand this whole light issue.

Chasgood, 1.3 wpg and 1.0 wpg are both LOW light. Its hard to say they'd be the same or different. I don't think they'd be dramatically different, but I'm willing to bet plants would do a fraction better in the 1.3 wpg, IME. Light is just one factor, there is also the types of plants, substrate, fertilizers, co2, condition of water, etc.

HTH! I"m no expert, its just how I understand things here!

 

[chasgood]

I was using my Eclipse 3 hood as a example. It is sold with for use with the 20L, 29 and 37 gal glass as well as 40 gal acrylic tanks. But you get different watt per gal for each tank even thou they are all 30x12.
Maybe I should have used the 20L in my example above.
20L 1.9 wpg
29 1.3 wpg
37 1.0 wpg
40 0.95 wpg

I think a better rule of thumb is needed. Like the surface area or square inches of aquarium bottom.

 

[gone fishin]

I would just calculate the gal. and go higher light from there. 3WPG is a good start, it's only that bright brand new, then if it's growing good, you have a cusion from there. Any one reading posts that say, "I bought this light and it's so bright it sucks !" -crank it up ! You have to know what you want first. Taller tanks can require twice as much light as one half as big with the same footprint. Find some cool plants you like, and get a light to grow them. If your just trying to grow crappy plants with a crappy light you just get a crappy feeling in the end.

 

[Guest]

I doubt there will ever be a better rule of thumb than that WPG we have now. There are so many variables that it's almost silly. But height of the tank does have an effect. Not much of one but it does. As does the width and length of the tank. WPG works for the vast majority of people and tanks.

 

[vega]

Not mention the water color too. A tank using peats in filtering will have brownish water which will need more wpg then a crystal clear water tank.

 

[betowess]

O.K. I am going to throw another bolt into this stew. Try computing WPG with AH Supply's reflector which measures about 60% brighter than say Coralife or All Glass and similar big name PC aquarium light manufacturers. So by the WPG method, my AH Supply 55 watt is giving me a mere 2.11 wpg. But by using AH Supplies tested observation, its more like 3.38 WPG. Now, since I can grow the bright light loving Alternanthera Reineckii like gangbusters, I have to go with the 3.4 wpg interpretation rather than the standard WPG. This is one example of why a general rule should be individually evaluated.

 

[shawmutt]

 

[vega]

Just stick to wpg rule at moment. As for others parameter, probabily only experience will help.

 

[Guest]

O.K. I am going to throw another bolt into this stew. Try computing WPG with AH Supply's reflector which measures about 60% brighter than say Coralife or All Glass and similar big name PC aquarium light manufacturers. So by the WPG method, my AH Supply 55 watt is giving me a mere 2.11 wpg. But by using AH Supplies tested observation, its more like 3.38 WPG. Now, since I can grow the bright light loving Alternanthera Reineckii like gangbusters, I have to go with the 3.4 wpg interpretation rather than the standard WPG. This is one example of why a general rule should be individually evaluated.

Nothing personal but the AH Supply reflectors are not "magic" but they are efficient. They do get more of your light energy into the tank. AH Supply fixtures are brighter, and do bend the WPG rule but don't break it. The WPG rule was formulated without the knowledge of the AH Supply reflectors. If all light fixtures had reflectors as good as the AH Supply reflectors the WPG rule would reflect that and a high light tank would more likely be in the 3 WPG range.

 

[betowess]

Well said Rex. But 60% brighter is still 60% brighter.

 

[Guest]

But they are not brighter. Brightness comes from the bulb. They are more efficient. They get more light into the tank.

 

[waffleman]

I believe the real answer is that what is important is the Lumens that the light puts out.
As one pointed out a PC of the same wattage will put out more lumens (units of light) than a regular fluorescent bulb.

What goes along with brightness is the Color temp. of the bulb. What our eyes/brain belive is brighter, may actually be the same if not even less lumens.
i.e. an actinic bulb puts out the same amount of light than a 10000K bulb yet it looks totally different, but the corals love the intensity that we can not see.
The fact of using a reflector only prevents loss of light, and redirect it towards the water.

I too use the WPG as a rule of thumb, just a lot easier and it gets you close.
m2c
Waffleman

 

[julicat]

I have a Coralife PC with a 50/50 bulb set and 28 watts (that's the bulb it came with). As I have a twenty gallon tank, I understand I should have a higher-wattage fixture (which I can't afford). Nonetheless, I've been told I should get a different bulb set for the benefit of the plants. But in the end nothing I do will make my 28 watt PC sufficient for a lushly planted tank, yes?

 

[betowess]

You might do O.K with some low light plants like Java Fern etc., if you get a 6700K lamp and toss that smartlamp. But yes, you need more like a 65 watt coralife or a 55 AH Supply setup would be nice, IMO.

 

[malkore]

AH reflectors simply do not provide any more light than what the bulb is already rated at. What the reflectors do is grab up to 60% of the light that was being lost due to restrike (the top half of the bulb, basically) and divert it back down to the tank.

So if anything, without AH reflectors, a tank with a 55watt bulb might only be sending 30watts down to the plants. With the reflector, you're getting as close to all 55watts reaching the plants as you can get.

As Rex said, they aren't magic reflectors....but they are REALLY good.

 

[shawmutt]

soooo...the wpg rule is more accurate when using AH reflectors?

 

[waffleman]

Julicat,
the 50/50bulb will encourage algae growth. I would get a 6700K or 10000K bulb. Those 50/50 bulbs are great for reef tanks, as they need coraline algae.


Waffleman