African violets have unusually low light requirements therefore you should ask this question in the African Violet forum.

I suspect that your African Violets have all the light that they need from the window. If not, you would be better off using one or more of these 8.5 watt LED bulbs:

http://www.homedepot.com/p/Philips-60W-Equivalent-Soft-White-A19-LED-Light-Bulb-2-Pack-455576/205815532

Incandescent bulbs sold for plant growth are a scam.

Using incandescent bulbs to grow plants probably is not any less efficient than using regular fluorescent tubes. The chlorophyll in plants absorbs best in the deep red region of the spectrum (660-670nm wavelength) and regular fluorescent tubes simply do have these deep red wavelengths.

"Using incandescent bulbs to grow plants probably is not any less efficient than using regular fluorescent tubes. "

Not true. Whereas it is true that, "The chlorophyll in plants absorbs best in the deep red region of the spectrum (660-670nm wavelength) and regular fluorescent tubes simply do have these deep red wavelengths.", your first statement does not logically follow because plants have accessory pigments that cause photosynthetic action spectra to differ substantially from the absorption spectra of chlorophylls. Photosynthetic action spectra have been empirically measured. See:

http://www.general-cathexis.com/images/ActionSpectra001.png

http://www.general-cathexis.com/images/ActionSpectra002.png

http://www.general-cathexis.com/images/ActionSpectra003.png

and note that light at 611 nm is typically 95% as efficient as light at 660 nm. Most typically, the red light in fluorescents peaks at 611 nm.

Excellent post, aruzinsky. I did not realize that.

However, I will point out this: A white light source that contains longer wavelengths of red light will contain substantially more red light, because the human eye is less sensitive to those longer wavelengths, and in order for the source to be white-balanced there needs to be more of that red light.

Yes, but you meant "proportionately more red light" otherwise someone might falsely conclude that incandescent is better than fluorescent. But, I have often used this rationale to advocate the use of typical 2700 K household LED bulbs over typical fluorescent bulbs which have the same lumen efficiency.

Aside from photosynthetic efficiency, the proportionally large amount of far red light, > 700 nm, from incandescent bulbs will cause many plants to etiolate via a phytochrome reaction. See https://en.wikipedia.org/wiki/Phytochrome . I am uncertain whether this would be a problem with African Violets.