Glowbulbs are powered by the sap of the plant they are a part of. It is possible for a glowbulb to exist as a separate device, which is then powered by placing it in sugar water. However, this is difficult in practice as the glowbulb is a living thing, and therefore must be kept alive even when not in use.
Glowbulbs are usually part of telehorticulture networks. Since the vines used in telehorticulture already allow sap to shift between large numbers of plants, it is relatively simple to divert a small portion of this sap to power lights. They are also used as street lighting in wood cities.
Because glowbulbs require external energy input, they have limited use away from telehorticulture networks. In such locations, it is usually simpler to use more self-contained light sources.