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1947-48 Theatre Catalog, 6th Edition, Page 267 (253)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 267
Page 267


1947-48 Theatre Catalog, 6th Edition, Page 267

medical instruments or mysteriously spotlighted signsehave a tendency to overshadow other important, though less obvious, uses for the phenomenon. Designers take advantage of light-piping in as simple an article as a Plexiglas jewel chest or cigarette box. In a traditional design, using right-angle core ners and square bottoms, the top edges of such a piece are dull and lifeless because the light simply passes from the top edge through to the bottom. If, on the other hand, the sides and bottom (or the ends and bottom) are formed as a single curve piece, the top edge will be brillianteglowing with the light that enters one edge emerging from the other. When curved sides or ends are not desired, it is often practicable to bevel the bottom corners to 45 degrees and thus secure considerable edge brilliance (Figure 6).

Edge-lighting can be achieved by excluding air from a surface without actually destroying the surface, Any material which adheres tightly to the plastic and thus excludes the air will glow when seen from the opposite side of edge-lighted sheets (Figure 7). Such coatings produce the same result as





Surface

critical angle = 42 .20

FIGURE SeThe critical angle describes the angle between the light ray and an imaginary line perpendicular to the surface. It is more practical, however, to employ the complementary angle.

shading or engraving the surface; that is, they change the angle at which light beams striking the surface are reflected.

The coating or machining, being the immediate source of the escaping light, appears to glow. Obviously, since the flowing design is due to internal reflections, the design is more brilliantly lighted when viewed through the surface opposite the interruption than it is when seen direct. In the former case the light seen is reflected from the interruption and is nearly all visible, but in the latter instance, the only light visible is that which has been able to escape through the interruptions. Opaque paints are often used in producing edgelighted designs and these, of course, must be viewed through the plastic.

The most brilliant edects are obtained when all possibility of light transmission is blocked since a portion of the light in an edge-lighted panel will be transmitted if the interruption is not opaque. Machined or embossed designs, for example, may be filled with opaque pigments of the proper color. Unpainted, sand-blasted surfaces are brighter than simple machined areas since they are more irregular.

1947-48 THEATRE CATALOG

NO YES (2)

(l)



YES (3)

FIGURE Gain a traditional design, using right-angle corners and square bottoms. tap edges are dull and lifeless because light simply passes from the top edge through to the bottom (1). If the sides, ends. or bottoms are curved or beveled, the top edge will be brilliant. glowing with light that enters one edge and emerges from the other (2 and 3). Style of the article determines method.

PRODUCING EFFECTS

A variety of techniques is available to produce different effects (Figure 8). A painted design glows with a uniform diffuse light but actual cutting of the plastic surface produces sparkling highlights, An engraved line appears most brilliant, seen directly, if given a "V" profile. A foll profile reflects a thin highlight from any angle. A square groove is not well lighted on the flat bottom, but is brilliant on the sides which are least visible.

Scribing, as distinguished from engraving, consists of closely spaced lines and is reminiscent of dry-point etching. Since these lines are microscopically rough they are evenly lighted at any angle. Highlights, in this process, are made by using masses of fine lines. Since there is always some of the original sure face not disturbed by scribing, the reflection of the light is extended from one interruption to another, and a uniform illumination results. Many pleasing results are obtained by combining several techniques.

Painting in Light

If the edge through which the light enters the sheet is colored with a transparent dye, a white painted or an engraved design on the sheet will be similarly colored (Figure 9). If different colors are spotted along one edge, blended colors in the design are produced (Figure 10). One technique, known as upainting in light" has been found especially effective. It is produced by engraving parts of the design on successive sheets of plastic so that when bound together an entire scene is rep resented. The edge of each sheet is colored as desired, and when edge-lighted the complete scene appears in depth, light, and color.

There are endless variations for this process. If desired, some of the engraving can be placed on each side of all but the top sheet. The back surface of each sheet, of course, redects the most light but the reduced brilliance of front surface reflection from the back sheets may be useful in certain designs. Paint and engraving may be combined for still further modification of the result. The distance betWeen the sheets may be varied or each of the sheets may be of different thicknesses. In some cases the designer may find it desirable to cut out sections from one or more of the sheets. If color is added to the edge thus formed, light of pleasing tint may be thrown on some other part of the design.

It is often desired to provide some sort of backing for an edge-lighted panel. This need be nothing more than a single sheet of paper or other material, and any color or design may be chosen. Such a background, being unattached to the sheet, remains unlighted when a design is illuminated.

Here again is one of the places where the originality of the designer can be used to produce almost endleSS variations in the effect. By having the background color match that of the design painted on the plastic a sign can be made to appear or disappear as the light goes on and off. If the edge of a sheet is colored red and the design is white against a white background, the design is only faintly visible when not illuminated. When the light is on, how FIGUBE 7-Paint, wax, or any material which disturbs the air-acrylic relation, will glow when the sheet is edge-lighted. Such coatings produce the same result as shading or engraving the surface: they change the angle at which light beams striking the surface are reflected. Any material which adheres tightly to the plastic will glow when seen from the opposite side of edge-lighted sheets.

Light ray





PAINT 0R WAX (etc)

surface

<- Light ray,hitting painted surfacediffuses

surface

This part of diffuse light hits the other surface steeply enough to escape
1947-48 Theatre Catalog, 6th Edition, Page 267