Shiny surfaces reflect light. This can be used to direct light to places we want it to go, but it can cause problems when the reflection is accidental and bright dazzling light is reflected toward the viewer.
There is no simple guaranteed solution to this problem, so designers need to be very aware of all the potential sources of glare and reflection. Glare problems are complex and cannot be avoided by designing on plan drawings; controlling glare requires the designer to constantly think in three dimensions and visualize the scene as the viewer will experience it.
All the projects in this book succeeded in avoiding glare problems, but some are particularly good examples, such as the St Mungo’s Museum case study in this chapter (see following pages 100–1) and One Gyle Square in the next chapter (see pages 110–13).
Right
Specular reflections of light sources on glossy surfaces can be particularly problematic in situations where contrast levels are relatively low, such as in galleries and museums.
Lighting for people 99
Exposure to light can be damaging to many fragile materials and this can be particularly problematic for museums and galleries. In order to protect sensitive objects, special conservation lighting standards are applied that restrict the amount of light that can be used to illuminate the exhibits. This leads to the common experience of very low light levels in museums and galleries, which can cause real difficulties for the lighting designermany minor lighting problems, such as glare and distracting reflections, can be greatly exaggerated when general light levels are low.
In exhibition lighting, preventing glare greatly aids the visibility of exhibits lit to conservation lighting standards. Glare and sparkle from badly focused, poorly positioned, or inappropriate luminaires provides the visual system with an excessively bright point of light by which to measure other lit surfaces. Our sense of “brightness” has no built-in scale; it is purely a relative assessment. So, by comparison with an unshielded or reflected light source, any exhibits illuminated to conservation lighting levels appear to be very dim and gloomy.
Glare can be a particular problem when working with exhibits that are behind glass. Minimizing distracting reflections requires a great deal of careful thought, planning, experimentation, and, above all, a lot of time spent perfecting the focus of each light source during commissioning.
We think of glass as a transparent medium. However, this relies on certain conditions. When the objects and surfaces beyond the glass are more luminous than any reflection in the glass, we can see through the glass. When the reflections in the glass are more luminous than the objects beyond, it can be difficult to see through the glass. This “veiling reflection” disrupts our view through the glass. This effect can be clearly seen in any street at night. As we walk along the street we are able to see into rooms that have internal lights switched on. It is dark outside and little light is reflected off the window glass, so we can see into the room beyond. During the day, the same room could be much brighter because of daylight streaming through the windows. However, the observer on the street outside receives far more light reflected from the bright sky and so finds it difficult to see into the room. Note that this effect has nothing to do with the difference in light levels during the day and night; it is about the relative intensity on each side of the glass. If we stand inside the lit room at night and look at the window, we are likely to see little more than ourselves and the room reflected in the glass.
In less extreme situations, distracting reflections can be created when there is a significant contrast between the bright points of a reflected light and the background they are seen against. This is particularly apparent with point sources such as spotlights, but can also apply to linear ones such as fluorescents. These problems can often be avoided
by repositioning the light sources, the reflective surface, or the viewer. People often unconsciously move position slightly to try to avoid reflections interfering with their view. This repositioning cannot always be achieved, so other solutions sometimes have to be found to deal with reflective surfaces such as glass.
Rather than directing concentrated beams of light from small sources such as spotlights toward the reflective surface, it is possible to light an object indirectly by bouncing the light off diffusing surfaces such as walls and ceilings. With skill and thoughtful design it is possible to minimize the contrast between the brightest and darkest surfaces reflected in the glass. With minimal contrast it is much easier for the visual system to see through any reflection in the glass to the objects beyond. This technique can be adapted to work for a seemingly impossible lighting task (see the case study on the following pages).
Below
Lighting the paintings on the end wall, with glass display cases below, presented one of the greatest challenges for the lighting designers. The specially created illuminated void above provides the diffused lighting required.