Yes, and in fact most aquariums do with under 1 watt per gallon. E.g. 55 gallon tanks tend to have full hoods equipped with 1 40W bulb. This is fine for fish and Java Ferns, Anacharis.
For those that don't know, or are interested...
Thought it's not really your question, I'd like to respond to the plant issue by saying that most planted tanks require more like 3-5 watts per gallon. This "rule" changes depending on how tall (deep) your aquarium is. If it's taller, you generally need more light to combat the diffusive properties of water. The general guidelines for "low" "moderate" and "high" light plants are these...
"Low" light plants (that *can* survive in low light, not that have to have low light) need at least 1 watt per gallon. These include Java ferns, anacharis and some Cryptocoryne species.
"Moderate" light plants tend to need between 2.5 and 3.5 wpg
. Most plants fall under this category, including Anubias spp., Hygros, Water Spirites, many "worts" and swords.
"High" light plants tend to need between 3.5 and 5 wpg
. Some plants, such as Glossostigma elatinoides need really intense light to simulate the tropical streams and rivers they come from.
Of course, other factors also come into play! Compact fluorescent bulbs generally deliver more lumens per watt, and so are better for plants... But this is all info for another thread!
, I keep 3 wpg
on my 10G planted and it does very well. I keep just under 3 wpg
on my 55 (150W) and the plants look beautiful (will post some new pix soon). With this much light, I also have to have CO2