Can a full spectrum light bulb serve the same purpose as a grow bulb?

The term “full spectrum” is misleading. In truth, it is about as informative as the label “lower calories” on a food product. (Lower calories than what?) Full spectrum lighting is not a technical term but a marketing term. The manufacturers want you to believe light from their bulbs duplicates natural daylight. In fact, full spectrum bulbs from different companies neither duplicate natural daylight nor do they compare well with each other. There is no standard by which manufacturers can or must measure their bulbs labeled “full spectrum.” And they are anywhere from two times to ten times more expensive than other bulbs. The light required by plants depends on the type of plant and their natural environment. Grow lights are designed to have a balance of light rays found favorable to most plants. On the other hand, full spectrum lights are usually marketed to people concerned about Seasonal Affective Disorder (SAD), which is believed to cause some people to have negative emotional and physical responses to the lack of natural daylight during winter. Comparing the two as categories is impossible, comparing one specific bulb to another specific bulb would be difficult but more fruitful.

A good and inexpensive solution to your problem is to get some of those compact fluorescent bulbs. While a specialty grow bulb would be the best choice because they’re designed for the purpose, they aren’t cheap and I’m not sure if they make compact models (if you’re still interested, you might have to check out what the optimum spectrum is for your plants in order to choose the right one).

Fluorescent bulbs give off a wider spectrum than incandescents, though likely at lower levels than a grow bulb, and can be used to grow plants. I have used them successfully in the past to supplement natural daylight.