I’ve got firefly petunias, and while cool as hell, IRL they are very dim. (Most of the time at least. There are occasional days they are especially active). You need to have either no or low competing light, and be somewhat dark adapted to see them. A street light 2 houses away can completely drown them out so that you’d need to put them in your shadow to see. Note that the still curled up new flower buds are the brightest, and more comparable to glow powder that was charged and left to dim for an hour.

It’s very difficult to actually take a picture of them to accurately show the level of glow. Either your camera is unable to focus on them, or it does too good a job at amplifying the low light, making them seem way more impressive than they are.

Fundamentally, emitting light has a significant cost in ATP, so it’s not practical to simply tell the plant to dump more energy into doing so. A smarter person than me might be able to estimate how many luminaries you’d get per some unit of ATP. Firefly petunias also need full sun throughout the day large or they get leggy and don’t do great.

There are a few things which could make plants as lights more conceivable:

1. Somehow fixing the release of luciferase enzymes to dark conditions only (currently the glowing is always active). I have bioluminescent dinoflagellates that only glow during the times they expect it to be dark, because that’s when they’ll release an enzyme when disturbed. In contract to my petunias, these are very bright, enough to read with, for a single second anyways.

2. Somehow modifying the cellular structures to allow more light to escape like actual fireflies. (https://www.psu.edu/news/research/story/firefly-inspired-sur...) Currently much of the light is reabsorbed internally, and this only gets worse with pigments as shown with crossbreeding with other colored petunias. (https://old.reddit.com/r/FireflyPetunia/)

Both of these things are going to be extremely hard.

All that being said, yeah I’d love turning every plant in a park from grass to trees a glowing equivalent, but I’d not ever expect them to provide street lamp level of light. But if you have an area that becomes too dark to see the grass and aren’t going to put up lights anyways, then that’d be a perfect place for such plants.