This applies to plants that exposed to high levels of ultraviolet in order to cause a biological reaction in them. In the case of tomatoes, peppers and other edible plants, it forces them to produce more flavenoids, making them taste better. In the case of cannabis, it forces the plant to produce significantly higher levels of THC, as THC absorbs ultraviolet and serves as the plants only defense mechanism from UV.

The goal of stressing is to push the levels of UV to at least as high as the natural sun, or even higher, up to the point that it causes minimal damage to the plant. This high level is what forces the plant to change modes from growth to resin production, and is generally used during the flowering and fruiting portion of the plant cycle.