Good thinking. More light can increase growth for at least some plants. The problem is mostly the cost of the power and equipment. Plants getting more light will probably also need more water. Can you figure out why?

You might want to consider a career in botany, agriculture, or plant ecology.

Yes - this is actually a way that the FDA catches marijuana growers, because they keep these greenhouses full of plants with lots of bright lights on at night, which consumes a great deal of power. The police can see if someone has been doing this just by looking at their electricity bill.

The problem with doing this on a scale that would be sensibly economical is that artificial light costs energy, and that energy either comes from sunlight, from fossil fuels, or from nuclear power, all of which mean (for different reasons) have less energy during the daytime when the sun is shining. Thus unless you're trying to grow a small amount of a very expensive (and secret) crop - like the aforementioned marijuana growers who don't want to grow above ground because they'd be spotted - using lights to grow plants double-time just isn't practical. You can do it, but there's no reason to.

Artificial light does help plants that do not receive good quality light indoors for sure! And in regions where there are long days (e.g. Alaska in the summer with 18-20 hours or more of sun), many crops bloom like crazy (try searching Google images with the search term "alaska giant cabbage" - those things are huge!)

However, artificial light at night may not be the best for all plants. Light can serve as a signal for plants to enter into different stages of growth and development. Darkness may be required for a plant to be able to properly develop. A plant may be fine for short periods of continual light but may not grow as well if it is constantly kept under light all the time. Artificial lights can also get pretty hot and can overheat the plant, causing wilting or even frying the plant. This sounds like it might be an interesting science fair experiment to do! Thanks for your question!