The light is a factor allowing us to see - to perceive shapes and colors.
Whether we're looking at a work of art, whether it's a breathtaking landscape or a shabby wall - the picture reaches our eyes through the the light waves emitted by the light source and reflected on the surface of the things we're looking at. However some of them are made of translucent materials. They have ability to reflect but also to pass the light rays.Those materials are: water, air and so the glass. To see the opaque objects in the reflected light the viewer must be located in the same space as the light source. With the translucent materials it's the opposite. The stained glass and fused glass windows have to be watched against the light.
In consequence, the room in which the viewer is located, must be darker than the space behind the glass
So if the stained glass panel is applied to the window there is no problem- these are the perfect lightning conditions for glass windows.
If the stained glass is situated between two rooms it will be visible in all its glory only with a considerable difference in brightness between those two spaces. In that case, the stained glass will work properly for those in the darker room (in the transmitted light). In the brighter one it'll look more like mosaic, flat and desaturated (in the reflected light).
If the level of brightness in two rooms is the same and we want it to make the stained glass noticeable, we must consider artificial lightning. Placing the reflector on one side, we have to be conscious that the stained glass panel will be well visible only from the opposite side.
It's not the amount of the light that counts but difference in the brightness between two spaces.
In short - we have to decide which side of glass panel is the one we want to expose and place the spotlight on the opposite one.
The picture below explains the issue.
Naturally, we can place the spotlight on both sides of a glass panel and use it alternately, depending in which room we actually reside. The best kind of reflectors to lighten up our stained glass panel are the ones with adjustable beam and light intensity. This kind of spotlights is applied frequently for museum lightning.
In big front window of our studio we show art glass. When it is dark outside we turn on the lights inside our studio and people passing by can observe the gallery of art glass.