Unless you have metal halide lighting you'll never have enough light.

is it expensive to light a 150 gallon tank for plants?

Tropicals and most hardy require a minimum of 6 hours of full sun to even think about blooming and growing properly. YOu can make a small hardy grow ok, i f your not looking for daily day after blooms out of it, and they do not get excessively large.
MOst typical aquarium hood lights are not sufficient for proper growth of lilys though.

I do have a 55 gal setup which is kept outside in the gazeebo that has had a hardy variety (Helvola) lily in it for 2 or so years now and doing good. It gets a sufficeint amount of sun but it still does not do as good as it could or as good as the same plants divisions do in full sun..

For normal underwater plants [crypts, swords, etc] it's not too expensive but water lilys need at least 4 hours of full sun to bloom. Metal halide or sodium lamps are expensive to buy [@ $200] and run [200-400watts]. Regular aquatic plants can survive on multiple florscent or high output florscent lamps [$25 shop lamps work OK]. Even most dwarf lilys are too big for the average tank.

Also keep in mind that above 2 watts per gallon you will need CO2 injection. For a large tank the yeast style ones aren't adequate. You can get some tropicals that have lower light requirements that are lillies (with much smaller flowers then what you have in mind) The problem is if uyou have to much surface blockage with larger lillies then other plants will be deprived, unless you provide side lighting. Cabomba flowers, also the "lily bulbs" sold at walmart.

woeisme, good point...light blockage

This used to be a fairly common goal back about 15 years ago, and was usually pretty easy of you were careful with the plant you picked. I had great success with N. 'Dauphin' in a 20 gallon long tank. This was usually the plant that was suggested, as it will flower in low light conditions. I had it flower year round with just 2 flourescent light strips - it never flowered with more than one flower at a tine, but it would send up a flower or three every month.

The plant was placed in a tupperware container with good lilly soil, and was fed on an as-needed basis - you can tell when the plant is growing strongly, and you feed more. I only had a couple of inches of headroom for the flowers, and I kept the temperature pretty hight - 78 - 82 F.

Joe 'it can be done' DeRosa

What about if you use reptile bulbs instead of aquarium bulbs though? Those bulbs for high uvb requirement reptiles might be good (iguanas, other herbivores, and desert species). I might just pull one of my lower output bulbs and replace it with a reptile bulb because I have a painted turtle I'm going to put in my big tank.

Would that maybe help with the light for growing lillies?

I use shoplights with phillips daylight deluxe bulbs they are 6500K. Usually aquarium plants reccomend between 5500K-8000K. I also used them to start seeds this past winter in the basement for the garden. They are available at Home Depot for about $6.50 for a 2-pak. Worth a shot. To get light below you can try to do it from the back or sides. I guess if this is what you are aiming for its worth a shot.

I have 4 compact flourescent tubes over a 125 gal. tank. The total output is about 320 watts when tubes are new. Since light yield drops as the tubes age, I've found that it is best if I replace bulbs on an alternating basis because four new ones create a lot of light. I have grown some of the "tiger lotus" waterlilies offered on mail-order sites. They do get too big eventually but you can grow them as submerged plants for a year or so by cutting off each leaf that reaches the surface. You won't get flowers but the leaf texture is very attractive among "grass-like" plants. I have Cryptocoryne species that grow leaves above the water and Echinodorus that flower in this tank. I don't think you would have any trouble flowering a waterlily in this set up.

I love the veriegated lilies in my tank. But as others have mentioned, they can be surface hogs and shade large areas of your tank.

I have been playing with lillies for a bit now since my previous post. A daylight bulb is sufficient for lilys.....with a temp of 6500K with 10K being better.....So far I have a tropical lily (Dauben) in a 10 gal tank for a bit more than a month now, and its been constantly in bloom and have had as many as 3 blooms at once on this one lily. Its a tropical, but it is very well suited for a small container as it readily adjusts to water level and its size constraints.....It is also known as the Madagascar Dwarf Lily....

I have a 20 gala tall with another dauben in it and it too is just fine, not quitea s great as the 10 gal setup, but then this lily was just planted from a cutting from the one in the 10 gal tank, so there is no doubt it too will do fine. Its leaves alal reach the surface without a proble.

In yet another tank along with the Helvola mentioned previously, I have a Charlies Choice. Its not a slouch by any means and its leaves etc also adjust readily to its container size. It grows quite vigorously and its a constant leaf factory on steroids. I moved the Helvola over to ne side and put the Charlies Chlice Lily on the opposite side...Both are still blooming just fine

As some one stated above they need 4 hours of light....they need 6+ hours of good light if you want them to bloom and remain in good condition, anything less is not going to give you good results.....

I can recomend the Dauben (tropical), Helvola (Hardy) or Charlies Choice (Hardy) for use in aquariums.....with the Dauben doing fine in either deep or smaller tanks, and the Helvola and CC needing a bit more space than a 10 gal but it should still grow and bloom but with these 2, your going to have to keep removing leaf growth sooner. Tropoicals do fine in water 70+ deg and Hardys in 60+ but all like water temps normally kept in a freshwater aquarium so will all do just fine........but use a 6500K or 10,000K temperature bulb if you want results.

When I had first set up a 90 gallon in my basement, I had 4 normal 40watt tubes over it (two phillips high par bulbs, 2 cool white bulbs). The tropical water lillies I had in there flowered no problem. They were what the pet stores sell as nympaea lotus (green tiger lotus). I later identified them as "Woods white Knight", night bloomers. Once I put two 150 watt double ended metal halides over the tank the leaves never even came close to the surface as they had ample light toward the bottom of the tank, hence, they never flowered again. The banana plants I had (Nymphoides aquatica), on the other hand, loved the very high light from the HQI's. They got so out of control I ended up pulling most of them out. I would regularly bring dozens of plantlets to pet stores and give them away or trade for coral fragments or fish. I even brought a few mother plants to Hanover Pet and Adam's Pet Safari (both in NJ) and most people thought they were lillies due to the size of the floating leaves and legth of the stems. They also flowered regularly. The banana looking storage tubers (for lack of a knowing the actual term) do not exist on mature plants. If I can figure out how, or someone can tell me where to post a picture of the tank with the lillies I will.

another angle you might take is to only allow underwater leaves to develop and clip any floating leaves. you lily will not bloom like that but you will get terrific underwater foliage and you won't need all the light requirements mentioned above. in this case, sufficient light would be a detriment. put it in its own pot with some heavy clay topsoil. and it will do great. the temp is the important part, high 70's. If you want it to bloom, take it outside in full sun, fertilize it and you will have more flowers than you can shake a stick at. (not in winter of course) and just as a side note, N. 'Tiger Lotus' is so similar to N. 'Missouri' that the two are often confused. if there is clarification needed on that topic, email me.