Illumination is one of the most essential characteristics of stained/leaded glass. Without it, the most intrinsic quality of this medium is lost. Therefore, it is evident that lighting is a crucial element.
Traditionally, stained glass windows relied on natural sunlight. And this is still very much the case with stained/leaded glass. But as this medium made its way into our modern world, artificial lighting is also used today.
As far as which type of lighting gets used, natural or artificial, this really depends on the individual nature and type of each project and its feasibility as well. Sometimes it’s strictly natural; sometimes it’s strictly artificial; sometimes it’s a combination of both. It all depends, really.
The aim is to have the most optimum appearance and presentation in the final product. How this is achieved depends exclusively on the knowledge, skill and experience of the designer/artist according to the architectural vision and layout of the environment.
It is a factor that is considered and optimized in a custom manner uniquely for each project.