Hey Kadra...You can likely go to a hardware store, garden center, or even a hydroponic supply store. Sounds like your grandma has an incandescent grow light bulb, which is what I would ask one of the associates at the store to help you find. Generally, these lights are used as supplements to natural light and will not completely replace them. There are other types of grow lights, but these require special manifolds to house the bulbs. An incandescent grow light bulb will fit in a normal light socket. The important thing for these grow lights is that they produce relatively more colors in the spectrum of light that the plants use for photosynthesis. Those colors are specifically red and blue. The light may still look to be white when you look at it, but it should be producing more red and/or blue light for the plants. I'm not too sure where you can buy these bulbs online, but I'm sure a simple web search on "incandescent grow light bulb" will result in some fine sites. I hope this is helpful. Let me know if you have any further questions...Dr. Robby
