I'm not sure about the lower end of the spectrum on what benefit the plants will actually get from the light. You should replace the bulbs with something in the 6500K range or higher.
Yep, sorry about that. Full sunlight is a broad range we can't even get close to with regular bulb lighting. I believe in that range, it amounts to the same thing as very weak light plants would be getting only at sunrise and sunset. More like a soft, warm, yellowish desk lamp - regardless of brightness or wattage. To thrive, plants need a certain amount of daytime light.
Visibly, we can't tell too much ourselves. So if something seems bright to us, we tend to think it's good for plants too. But it's not just brightness or wattage or adding more time.. it needs to be within a certain spectrum to be usable light for plant growth.
Why don't you tell us more about the fixture itself.. what kind of setup this is? Lots of members here can help you find appropriate bulbs for just about anything. There are fluorescent grow lights for various kinds of sockets.. bright daytime CFL bulbs for regular household lamps. We know many inexpensive DIY suggestions for substandard (for plants) lighting.. plus inexpensive sources for retrofit kits. No need to limit yourself with what you're starting with. And there are practical options you can choose to get full advantage from what you already have without having to go out and buy a pricey new fixture.
By that, I guess it's not a "standard" fish tank strip light. Then, here you are.. get these from any department store lighting section, some grocery stores, and hardware places like Home Depot or Lowes. The brand name on the package doesn't matter, unless you have a quality/standard preference. But see how the 6500K spectrum is real easy to see on the package.