Ceilings become transluminous

Glare is caused by significant differences in brightness between conventional luminaires and the field of the ceiling. Glare can reduce a person’s visual comfort and productivity.

It may be a stretch to describe variations in a luminous ceiling surface as a ‘biophilia’ strategy, 
but natural environments have non-uniform illumination—clouds constantly change the skyscape, and walking under a forest canopy animates light and shadow. Like the patterns in stone, wood, or a patinated metal, variation can make a surface more interesting. The eye easily adjusts to subtle variations in brightness.

Some luminous ceilings earn recognition as biophilic by offering graphic or simulated representations of the sky. Several companies, for example, offer light-transmitting photographic panels that are very realistic, especially when set in recessed frames enhancing an illusion of depth. The authors have experimented with artificial ‘leaves’ installed above luminous panels; the leaves sway gently in response to airflow and vibrations to cast moving shadows emulating a mottled arboreal canopy.

Another approach is to program red, green, and blue LED lamps to replicate circadian changes in the color of skylight and the movement of simulated clouds. (Red, green, and blue [RGB] are primary colors of light—they can be blended to create white and any color of illumination.) The same technique is used to change the scene and establish a mood according to the time of day. Restaurants, for example, can change the color for each of their dayparts—soft lighting for the breakfast trade, full-spectrum daylight to hurry crowds through the lunch rush, warmer hues to relax diners, and pulsing colors for nighttime revelers.

Alternatively, colored LEDs can be used as pixels to turn luminous ceiling panels into a dynamic canvas for entertainment or to communicate vital information. Visitors to a hospital, for example, can be given a transponder that communicates with the ceiling to create an overhead yellow brick road leading to their destinations. Emergency lighting can flash panels in sequence to direct occupants to exits.

Another option involves rear projection. In this strategy, translucent and frosted ceiling panels function as screens for video or still images projected from above. This can be used to create sky scenery, art installations, or entertainment displays. The option is also receiving interest from retailers 
and the hospitality industry for branding and promotional placements.

These translucent panels have 32 percent transmittance; they would provide even more uniform light diffusion if lamps were spaced closer together. The panels reflect 50 percent of light from below, making them practical for use with indirect light sources to provide hybrid lighting schemes. Frosted panels with approximately 77 percent transmittance and nine percent reflectance offer significant improvement in energy efficiency while still providing a modicum of light diffusion. Clear panels with 88 percent transmittance have found use due to their unique functional and aesthetic properties.

Architectonic considerations
Various architectonic considerations are explored in the following paragraphs.

Fire safety
It is important to specify thermoformed panels with Class A surface burning characteristics and self-extinguishing plastic composition. Class A indicates 
a 25 maximum flame spread and a 450 maximum smoke development when tested according to ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials. Self-extinguishing vinyl is V0-rated under Underwriters Laboratories (UL) 94, Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances. It is critical to always comply with any requirements of the authorities having jurisdiction (AHJs).

Hiding luminaires above panels helps create a clean, uncluttered ceiling—one of the principal reasons for using luminous assemblies. This can be enhanced by also placing fire sprinklers above ceiling panels that will drop out when exposed to heat, which is a characteristic available with some thermoformed vinyl ceiling products. The thermoplastic softens at approximately 57 C (135 F), before sagging and then falling to the relatively cooler floor without melting or burning. This allows heat to rise to the now-exposed fire sprinklers so they can activate at about 66 C (150 F) and do their duty.

Drop-out ceilings must comply with National Fire Protection Association (NFPA) 13, Standard for the Installation of Sprinkler Systems, and be listed or approved by building code evaluation services such as International Association of Plumbing and Mechanical Officials Uniform Evaluation Service (IAPMO UES), FM Global, and UL. As many local AHJs have limited experience with drop-out ceiling systems, it can be useful discussing the topic with them while still preparing construction documents.

Sprinklers and related piping should be located where they will not cast unacceptable shadows on the luminous ceiling.

When acoustic vibrations (i.e. noise) impinge on the bottom of a lightweight suspended ceiling panel, the panel acts as a diaphragm and transfers mechanical energy into the above-ceiling cavity, where it is dampened by the viscous mass of air in cavity. Tests following ASTM C423, Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method, should use Type E mounting to hold specimens above the test chamber floor to simulate cavity depth.

While results vary depending on manufacturer, material thickness/formulation, and panel style, thermoformed ceiling panels have noise reduction coefficients (NRCs) of about 0.25 or 0.30 with a backer panel. Perforated panels can have an NRC of up to 0.40. These values make thermoformed panels suitable for a wide range of occupancies. Additional noise reduction can be obtained by installing acoustic insulation in the ceiling cavity.

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