Watts and Gallons?

[Kalavek]

This has been driving me nuts ever since I started researching tank options and recommended lighting for tank setups. I want to be set straight on this once and for all.

Mention plants in a tank, and everyone starts spitting out recommended "watts per gallon" numbers, but the they feel useless to me. I'll try and explain why...

First, the Watts: When I was taught stage lighting for film, the two important numbers were Color Temperature and Lumens. The only thing Watts described was the amount of power it took to produce those Lumens. You measure the light with a light meter on the stage, not at the wall with a multimeter.

Second, the Gallons: This is a volume, and does not at all describe the depth or dimensions of what you are trying to light. Plants don't care how much you're spending on electricity, they care how much light reaches them - and in water the distance between the light source and the plant must be considered. A depth one foot is fairly easy to light, while a four-foot deep tank will give you a bit more of a challenge.

These days the lighting industry is spending oodles of money researching ways to produce more lumens per watt. CF bulbs are a perfect example - fifteen watts into one of those will give you roughly the same lumens as (wild guess here) a 60-watt incandescent bulb. So how anyone can relate Watts to a measure of light is beyond me.

So, why say I have "1.4 watts/gallon" when I feel I should really be saying I have "2900 lumens at 5000k on a 45 gallon tank, with a depth of 18 inches"?

I'll admit it seems more complicated, but it does so much more to describe what you *really* have for lighting!

Now, have at it - shoot me down for not seeing something obvious. Please.

 

[Chris_A]

You've hit the nail on the head actually. Watts/gallon is nothing more than a rule of thumb.

So the lumens will describe the total amount of light leaving the lamp but what you really want is LUX which is the measure of lumens/ ft squared (IF I remember correctly... might be a different area unit, point is still the same though) Thats where light meter's come in and why there is the watt/gal guide line, most people don't care to or can't afford one.

You are also correct about the color temp. I don't care how many watts a lamp pulls or how many lumens produced if the color temp is 2000K (extreme example).

The other factor that you don't seem to see talked about in freshwater is PAR. The actual amount of that light that is usable for photosynthesis.

If you start looking *in depth* at reef lighting all of those come into play.

Chris

 

[Kalavek]

Oh good, so I'm not going insane!

You are correct, there are a number of other types of measurements that describe lighting very accurately. I can't remember half of it now, and going over all the different factors (directional light vs omnidirectional light, what reflection and refraction does to light, etc etc) would have just been confusing... so I stuck with Lumens as the most likely unit to be recognized.

And actually I made a slight mistake up there, these bulbs are supposedly 2700k - but it took some googling to find that number. Your "2000k" comment comes into play here - these bulbs are Philips "Plant & Aquarium" T8 tubes, and they raised some very different opinions in the forum I'm flipping through.

Several people began talking about the red end of the spectrum versus the blue end, and which color temps were needed for reef tanks versus planted freshwater - others referred to the output charts and stated quite flatly the bulbs are useless. But on the other hand, a couple people claimed to have been using the bulbs and found they work very well for everything they have put under them.

Here is a link to the forum I'm looking at:

Philips Plant & Aquarium - Growing under Lights Forum - GardenWeb

Any thoughts on this? The bulbs were inexpensive, so it wouldn't be a huge loss if I made a mistake buying them, but as far as I'm concerned the numbers mean nothing if the product actually works as advertised.

 

[brian1973]

On that note I will be following this thread as I will be starting building my hood to go along with the stand in a few weeks and I am going to do all the lighting myself, I have always understood lighting the way you described as well. We have had a few discussions on it in the past but everyone tends to stick to the WPG rule.

 

[Kalavek]

On that note I will be following this thread as I will be starting building my hood to go along with the stand in a few weeks and I am going to do all the lighting myself, I have always understood lighting the way you described as well. We have had a few discussions on it in the past but everyone tends to stick to the WPG rule.

Well, it's not just here on this board - everywhere I looked for info on figuring the correct amount of light for a new setup, I saw the WPG rule used like it means something. I just couldn't decide if I was being a fool.

So now I have to wonder what would be a better way of deciding where to start with lighting, short of finding some tank lighting guru who knows all the variables and has tried all the bulbs on the market and somehow knows what specific plants thrive under whether the numbers fit or not...

Bit of a tall order?

 

[brian1973]

Avalon is the hands down plant expert here IMO..he knows his stuff. Just remember you can still experiment and form your own opinions.

 

[Orion]

So now I have to wonder what would be a better way of deciding where to start with lighting, short of finding some tank lighting guru who knows all the variables and has tried all the bulbs on the market and somehow knows what specific plants thrive under whether the numbers fit or not...

Bit of a tall order?

And that's exactly why people tend to use the WPG guide. Tell me who in their life time could sit down and try out every combination of bulb from every manufacturer and not die an old man before it's over?

And a lot of people are scared off from planted tanks because they think the whole light aspect is too complicated as it is when people talk about the WPG. If everyone went by the LUX that would probably just discourage more people from getting a green thumb. It's all about accessibility. Once you've got the basics down and understand why some plants need more light to do better in some tanks than others, then you can get into the deeper subjects like LUX and what not, but to have a successful planted tank you don't have too.

 

[Lotus]

This article has a comparison of various bulbs (PAR, lumens, etc.), if you feel like getting technical: Aqua Botanic-light bulb comparison

The chart was done a while back, and there are a lot more bulbs on the market these days.

In addition, compact fluorescent and T5 fixtures have become much more popular than NO (normal output fluorescents). It's just a lot easier to get enough light in the space above a tank with smaller bulbs.

If you'd rather get recommendations, just let us know your tank size/dimensions, what kind of plants you want, and whether you will have pressurized CO2.

 

[Kalavek]

And that's exactly why people tend to use the WPG guide. Tell me who in their life time could sit down and try out every combination of bulb from every manufacturer and not die an old man before it's over?

This article has a comparison of various bulbs (PAR, lumens, etc.), if you feel like getting technical: Aqua Botanic-light bulb comparison

If you'd rather get recommendations, just let us know your tank size/dimensions, what kind of plants you want, and whether you will have pressurized CO2.

THIS is why I've stuck around here - real, useful advice and information! Thank you.

Lotus, that was an excellent article - and far too much for anyone half-normal to absorb in one sitting. I'll probably keep a copy of it around if only because it was so well researched and thought-out, regardless of any error factor it may contain.

In regards to my own tanks and applications; I'm not quite there yet, but I will be coming back to this topic. I need to get the two tanks I have sorted out first, there is still a lot of work to be done just on those!

Thank you all again.