The most common effect is the standard light box, primarily used to make self-illuminated signs. Architectural applications include luminous walls, ceilings, and backlit panels. The box is painted matte white on the inside and has rows of lamps mounted behind a diffusing material. The light box epitomizes the trade-off between efficiency, depth, and the ability to hide lamp images. For a shallow box, the lamps must be close together and the diffusing media must be very dense. White “sign” acrylic was developed to solve this problem; white pigment is added to the acrylic material, making it very dense even when relatively thin. Its transmission decreases and the “hiding power” increases with thickness; one common product is 45 percent transmissive at 3 mm (about .125”) thickness and 25 percent at 6 mm (about .25”). It is not uncommon to use 15 mm (1/2”) thick acrylic for very shallow signs to create a smooth, even light without lamp images or shadows (see figure 1). The depth of lamps behind the diffuser is about the same as the spacing between lamps. Using thicker acrylic allows the box to be shallower and the lamp spacing to be greater than the depth, although at about 4 inches from the face of the lamps, it is almost impossible to hide the lamp image of fluorescent or LED lamps with any practical material.

There are two other important variations on the light box:

  • An indirect light box uses hidden light sources to illuminate the back wall of the box, and the light is reflected back through the media (see figure 2). The media can be obscure (partially clear) and patterns on the back wall will be hazed, giving an interesting sense of depth.
  • In the gradient wash, lights hidden from view wash the acrylic directly at a grazing angle from behind. This effect can be accomplished with either pure white translucent or obscure media. With obscure media, the gradient wash can be combined with indirect wash to create a combined effect that has a gradient and depth.
FIGURE 1: In a standard light box, the box is painted matte white on the inside and has rows of lamps mounted behind a diffusing material.

When creating light box effects in architecture, be sure to investigate polymer bead materials. They have significantly greater transmission than ordinary acrylic, with surprisingly good hiding power. For instance, at 3 mm thickness, polymer bead can attain 85 percent transmission. Keep in mind the potential increase in brightness—you may find it necessary to dim the light sources.

In addition to these qualities, diffusion may be the result of light transmission through insulating material. Using layers of air-trapping material, insulating glazing panels can pass daylight by day and take on dramatic lighting qualities at night.

Among diffusing media, there are several distinct types with different qualities. Table Two - The Light Box: Alternative Light Panel Materials, reviews respective media and their qualities.

MIXED MEDIA

Beyond color and diffusion, glazing assemblies can combine several effects to create exciting new media. Included are:

Refraction
When light moves from one medium (such as air) to another (such as glass), light waves change angle as a function of wavelength. Lenses use the principle to magnify or focus light, while prisms bend light into patterns and rainbows. Refraction is a basic quality of glass, and it can be used to create a multitude of effects.

FIGURE 2: An indirect light box, a variation on the standard light box uses hidden light sources to illuminate the back wall of the box.

Apart from the conventional uses of lenses and prisms, specially made materials can embed refractive elements such as beads, mini-lenses, patterns, ribs, and linear prisms. This easily can be combined with other effects to achieve a mesmerizing result. For example, imagine a ribbed glass with an acid-etched smooth face, a combination just itching for the application of light.

Reflection
Obvious uses of reflectivity aside, some special reflective qualities can be used to create or further enhance the effects of glass or acrylic materials.

One current example is channel glazing, consisting of vertical channels creating air pockets between the front and back surfaces that insulate while creating an obscuring texture. Each channel is open, and light will enter a "light pipe" using the principle of total internal reflectance (TIR). If clear, the imperfections of the channel will be highlighted, but if one side of the panel is frosted, light will be emitted and diffused from that side, creating a textured, glowing wall.

Another possibility employs small pieces of specular reflectors used to create sparkle, one of lighting's most treasured effects. A product that achieves a sparkle-effect, Scintilla, uses a combination of channels and embedded small reflectors.One amazing product, Scintilla (www.sensitile.com), is a combination of channels and embedded small reflectors. Each channel behaves independently, so that both external incident light and TIR channel light can cause interesting sparkle effects. The result is a wall that seems to glow with static lighting and then scintillate when a moving source, such as video, is projected onto it.

These are just some of the special effects materials now being made to play with light. Part 3 will look at these materials and how they work as inspiration for lighting designers, architects, and interior designers alike.