Lighting quality
The decision to use luminous ceilings often begins as a strategy to improve lighting quality. Conventional lighting schemes—especially those using surface-mounted or recessed luminaires—result in ceilings having contrasting areas of brightness, ranging from intense direct light beneath fixtures to areas in shadow or only dimly illuminated by reflected or indirect light. Such variations in brightness create excessive luminous ratios that cause glare and detract from visual quality.
Glare decreases the comfort and efficiency of building occupants, especially if they are performing tasks that require visual acuity. This is made clear in the WELL Building Standard, a program advocating for the wellbeing of people that live and work within buildings. The standard repeatedly warns about detrimental impacts of glare, stating:
Non-diffuse, bright indoor lights create uneven levels of brightness in the visual field. The resulting glare… can cause visual discomfort (discomfort glare), fatigue, visual impairment and even injury (disability glare), and can be attributed to either direct or reflected glare. (This comes from the International WELL Building Institute’s WELL Building Standard, V1, Q2 2017 Version; Feature 55.)
The problem is exacerbated among individuals with poor eyesight—a special concern with an aging population. Consideration must also be given to individuals, including infants or the infirm who may be laying on their backs, looking directly into harsh glare. Light-emitting diodes (LEDs) can also often contribute to glare because they concentrate a strong light source into a smaller area than do incandescent and fluorescent lamps with equal luminous flux.
Luminous ceilings, on the other hand, typically provide diffuse illumination. While they can be designed to any level of illumination desired, their light emits across a large surface of relatively low brightness to distribute substantially uniform light and reduce glare. For this reason, luminous ceilings are frequently used in museums, showrooms, and other spaces requiring glare-free illumination.
Lighting design
Designers have traditionally wanted luminous ceilings to provide shadow-free, uniformly bright ceilings. For the greatest lighting uniformity and efficiency, structural elements above the ceiling, and the bottom surfaces of above-ceiling ducts and equipment, should be painted to have high light-reflectance values (LRV). This helps distribute light within the above-ceiling cavity to improve its uniformity; directing luminaires upward also boosts distribution by reflecting light off the structure. Above-ceiling equipment and services should be located to avoid casting unwanted shadows onto ceiling panels.
An alternative design intent that is now emerging welcomes non-uniformly bright transluminous ceilings; it allows the locations of above-ceiling lamps, pipes, and equipment to be ascertained from below. This has been fostered by several trends, including:
- widespread use of exposed-structure ceilings has accustomed the public to seeing the overhead ‘guts’ of buildings;
- desire to reduce energy consumption in buildings has created interest in luminous ceiling panels with higher light-transmittance values, trading light diffusion for lighting efficiency; and
- a paradigm shift from saturating rooms with high lumen levels to creating a blend of ambient and task lighting.
The standard material used for luminous ceilings has been translucent white panels with relatively low light-transmission values (LTVs) yet excellent light diffusion. In response to the trends just cited, thermoformed ceiling panels are also now made from clear and frosted clear vinyl; these options have higher LTVs that result in better energy utilization yet less diffusion.
The aesthetic potential of clear ceiling panels is just starting to be explored. Clear panels challenge the viewer’s assumptions about ceilings—is it a surface or an idea? A boundary that contains the room or a separator between adjoined volumes? Is the ceiling that which sits in the bottom of a suspension system, the bottom of the roof or floor structure above, or the totality of everything overhead? Is the meaningful architecture the ceiling surface or the mechanical art usually hidden above?
While architectural philosophers and critics argue the meaning and merits, we have already seen examples of clear ceiling panels that sparkle as light catches their edges and molded surfaces. They can be interspersed among opaque and frosted panels to create variations in light transmission and appearance, or arrayed randomly or periodically to reveal larger-scale patterns.
For their functional benefits, clear panels are used in computer server farms, laboratories, and similar spaces to separate the air in an occupied space from an above-ceiling cavity with different temperature, ventilation, hygienic, or other requirements while allowing for visual connection and borrowed light. These assemblies are also specified as peek-a-boo panels beneath equipment that needs visual observation or beneath spotlights and flood lights to semi-conceal the fixtures while allowing use of lower-cost, non-appearance-grade models.
