[saalweachter]

Doing plausibility calculations from another direction--

Let's say that we want to have a glowing forest. The glowing trees will absorb sunlight from a certain area and emit it over the same area with a certain efficiency.

Photosynthesis has an efficiency of between 0.1% and 1%. I don't know what the efficiency of glowing is, so let's assume it's 10%. So your plants will illuminate the area with about 0.01%-0.1% of the intensity of the light which they absorb.

Full daylight is about 100,000 lux, so your forest will be illuminated to somewhere around 10-100 lux, which is somewhere between "twilight" and "a poorly lit room".

It gets even worse if you want your plants to illuminate a larger area than they themselves cover: if you have a plant illuminating (say) 10x more area than it covers (a tree in the middle of an open field, or next to a road), you're down to 1-10 lux, optimistically.