# How much difference would this change make to my light levels?



## NatalieT (Mar 20, 2007)

I'm thinking of changing lights, but I can't figure out how much difference it will make.

The tank is a 20-gallon long (that's 30" long, 12" wide, 12" high)

Current light: 2x 23 watt spiral compact fluorescents. They are in a fixture intended for a 10 gallon tank, so that makes the light concentrated in one part of the tank, with dark spots in the ends. The places where the light is concentrated now are bright enough, but the dark spots are a problem. (And the short fixture looks silly propped up on this longer tank  )

Proposed new light (30" long):
http://www.petsolutions.com/Current-USA-Satellite-Powercompact-Lights+I42901004+C40001713.aspx
This has a single 65 watt bulb.

I can tell that the light will be spread more evenly along the length of the tank, which is good. What I can't tell is whether the "new" light will be *brighter* or *dimmer* than the brightest areas of the "old" light. Does anyone know enough to comment on this?

(If I could find a 30" fixture designed for 3 or 4 screw-in incandescents, I'd probably be delighted--I'd just swap in spiral fluorescents like in my current fixture. However, it seems that kind of fixture doesn't exist.)

Thank you!


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## aquatic_clay (Aug 17, 2009)

the new lights will make a very big difference. And that's a prett good price for them too!


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## NatalieT (Mar 20, 2007)

aquatic_clay said:


> the new lights will make a very big difference. And that's a pretty good price for them too!


I could tell the price is good, but I'm a little afraid of having too much light. I've got an "El Natural" style tank, and I don't want to deal with CO2, fertilizers, etc., so I don't want to "overlight" my tank.

I suppose if it is too much light, I can just be patient for a year or so--I've heard the light output on most bulbs goes down over time


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## aquatic_clay (Aug 17, 2009)

It might be too much for an el natural tank.

If the light is too intense then you could.

Raise the light higher off the aquarium to help with lowering the intensity.

or maybe even shorten the photo period by an hour.

Clay


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## NatalieT (Mar 20, 2007)

Thanks for the help, aquatic_clay. I just ordered the light. After seeing your suggestion to raise the light if needed, I realized I have another solution available, too: just let my floating plants cover the top of the tank to block the light. (They do that anyway if I don't pull them out regularly; if they light turns out to be too intense, I'll just deliberately allow the floaters to take over.)


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## Newt (Apr 1, 2004)

For one thing its a saltwater bulb in that fixture. With all that extra blue light being thrown from the bulb you will have a lot more photoreduction of iron. This can cause alge to appear with the excess 'free' iron now available in the water column. 

You will need to reduce your photoperiod also with the added light intensity.


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## NatalieT (Mar 20, 2007)

Newt said:


> For one thing its a saltwater bulb in that fixture. With all that extra blue light being thrown from the bulb you will have a lot more photoreduction of iron. This can cause algae to appear with the excess 'free' iron now available in the water column.


Iron in the water column? How does it get in the water column? I sure don't put it there!


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## Newt (Apr 1, 2004)

so your substrate has no iron and you add nothing with iron?


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## NatalieT (Mar 20, 2007)

Newt said:


> so your substrate has no iron and you add nothing with iron?


The only things I add are fish food, and water to replace evaporation. I never really thought about whether they might contain iron. The substrate might have some iron in the bottom level (dirt), but that's covered with sand, then with gravel (typical inert stuff sold for aquariums), and it's all buried under a layer of mulm. Since I don't get in there and stir things up very often, I don't think it'll be releasing much iron.

I already have some algae, and most of it doesn't really bother me. I scrape the front glass clean so I can see, but I like the fuzzy green background it makes on the back of the tank. Much easier than a moss wall! If I get green water, it'll be a great excuse to start a daphnia culture 

Since the new light uses about half again as many watts as the current one, I thought it might be about right; but it looks like the consensus is that it will put out a lot more light than would be expected from comparing the watts.

I guess I'll just have to watch what happens, and deal with problems if they arise. Thank you to everyone for the help!


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## Newt (Apr 1, 2004)

Watts are a unit of power consumption not light output. It is quite erroneous to use the WPG Rule.
If you dont use iron you dont need to worry about photoreduction of iron. You do need to worry about the actinic light bulb in the new fixture.


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## NatalieT (Mar 20, 2007)

Newt said:


> Watts are a unit of power consumption not light output. It is quite erroneous to use the WPG Rule.


I do know that, but power consumption is somewhat tied to light output, and I haven't heard of any other easy rule. All I really want is something a bit brighter than what I now have. I was sure that a single-tube fluorescent that only uses 20 watts would be dimmer than my current 46 watts, and a twin tube fluorescent would actually be more expensive than what I ordered, so I figured I'd give this one a try. (Besides, I do have floating plants that regularly block light from the rest of the tank, and they might come in handy if the light proves too intense; and, as aquatic_clay suggested, I could raise the light to reduce intensity.)



Newt said:


> If you dont use iron you dont need to worry about photoreduction of iron. You do need to worry about the actinic light bulb in the new fixture.


I didn't really think I had to worry about iron, but I also know that I don't know everything, so that's why I asked for more info. I know that other bulbs are available that fit the fixture I ordered, but I'll see what happens with the one it comes with before I decide about getting a different bulb.


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