Good question!

[aquariumfishguy]

I opened an email from someone asking a VERY good question and while I had somewhat of an idea how to answer, I still wanted your input.

I have a 20 gallon high tank and I upgraded lighting recently. anyway I bought the lightening so I could keep some nicer plants. I have what is called an eclipse florescent lighting strip and it says 17 watts on it. What i was wondering is, does this mean that it only puts off 17 watts of lighting? My incandescent had more than that so I thought this would have MEGA-watts! So my question is, how many watts is this 17 watt strip putting out and is this ok for a 20 gallon High?

...as you can tell, this is a confused person and I was getting confused as I read it which is why I posted it here. Any help and we'd both thank you! lol

 

[jdheff1982]

I can help ya!!! Most flourescents use about 15 watts of power, but produce anywhere from 40+ watts of lighting. That is why they are such energy savers. Think of it this way. You have 2 light bulbs. One is a standard 100 watt bulb the other is a 100 watt flourescent. Which one do think uses more power? Or do you think they use the same amount of power?? If you said that the standard 100 watt bulb uses more power, you are correct. The 100 watt flourescents can produce the same amount of brightness as a standard bulb but uses only 15 to 20 watts of actual power. So the bulbs on out tanks use 15 watts of power, but the brightness they produce is a much higher value.

Hope this helps!

 

[tomm10]

Watts refer to the amount of power used by the light. For axample you can buy a compact flourescent bulb to replace you incandescent bulb. The package will say something like "Replaces 60 Watt Bulb but uses only 15 Watts"

If you want to know the true output of light you need to look at the lumens.

That's the extent of my limited knowledge

I believe that the old "Watts Per Gallon" standard takes into account that you'll be using flourescent bulbs so his 17 Watts of light on a 20 gallon tank is a very low light situation.

 

[RTR]

Many folks are confused by watts and light output.

Incandescent lights produce much more heat than light. They are very inefficient. Fluorescent lights produce several times the light output per watt of power than do incandescents. They are not directly comparable based on watts alone, but a fluorescent will put out roughly 4 or more times the light at the same wattage. So your questioner will be getting much more light and less heat from the fluorescent than from the incandescent at comparable power ratings.

And the watts per gallon ratings commonly discused are based on standard (normal output or NO) fluorescent tubes, you are correct. PCF and HO/VHO or T5 fluorescents don't fit in the same approximation scheme either, as they are higher output than NO fluorescents.

 

[aquariumfishguy]

Thanks...that cleared a lot up for both of us. I shall email him this link to show exactly what you guys said. But I wanted to know, is that 17 watt florescent strip exceptable for the tank he has? I think last time he emailed me he did say that his plants all required low to moderate light.

 

[RTR]

In a word, no.

At less than one watt per gallon NO fluorescent, he is not going to be able to grow much beyond Java Moss and Java Fern, and that very slowly, little more than basically holing in place and size.

Edit: jdheff - you are confusing yourself, please don't add to the confusion of others. "Watts" are a measure of power consumption which has nothing to do with light. The power consumption of a 100W incandescent and a 100W fluorescent would be similar, except that the 100W fluorescent would use a bit more than 100W total, as you have to add the ballast power waste to the equation. Light output is a differnt measure, and there are multiple scales for that measure. Fluorescents are several times the efficiency of incandescents, so put out more light per watt used, but one 100W bulb/tube of each will each use at least 100W. Light emitting devices are sold by power used - the maker may brag about the light output in relation to other types of units, but if it is not labeled with the correct power rating, it cannot be sold in the USA.

 

[aquariumfishguy]

Ok that helps a lot RTR. I think in the process of helping this other guy it has helped me to.

...so I have a 20 watt florescent tube...which is slightly more than what this guy has on his 20 gallon tank. I have 20 watt tubes on all my 15, and 20 gallon fry tanks. Anyway, if I wanted to grow amazon swords and such, what wattage tube would I need to purchase?

PS: thanks for everyones help. Like I said, you helped both of us and Its made things much clearer.

 

[jdheff1982]

RTR: That's great, but... Why is it when I see a flourescent bulb that rated at 100W but says it only consumes 15W??? That's what I was trying t say earlier.

 

[Locust]

... because instead of rating light bulbs by the light they produce (lumens), light bulbs are rated by the power they consume (watts). It's convenient since it means having to remember a smaller number (a 60W bulb produces several thousand lumens) and while watts doesn't directly measure lumens, lumens is dependent on watts (i.e. more watts equals more lumens). So for most purposes, measuring light bulbs in watts is convenient.

But as RTR mentioned, flourescent bulbs are about 4 times as efficent at producing light then an incandescent bulb. This is why flourescent bulbs are often labelled as being equivalent to a much higher wattage incandescent bulb.

So your 15W bulb rated as 100W would actually be a flourescent bulb that only requires 15W of power, but produces the same amount of light as a 100W incandescent bulb.

 

[RTR]

Please, please be careful and accurate about stated power ratings - the ads on the side of the slipcase saying "equivalent to a xxW incandescent" do not address power ratings, but light output. Power ratings are legally required on the bulb/tube package and must give the actual power usage of the light. They cannot label a tube 100W unless it actually uses 100W. A 15W tube cannot be labeled 100W - it can say on the case it has the light output of a xxW incandescent - that is not power rating.

Light output is not legally required on the unit or package, but is frequently available.