GB1566553A - Transparency viewing apparatus - Google Patents

Description

(54) TRANSPARENCY VIEWING APPARATUS (71) We, LUCAS INDUSTRIES LIMITED, of Great King Street, Birmingham, B19 2XF, a British Company, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to transparency viewing apparatus.

The invention resides in transparency viewing apparatus including a housing having an opening at one side of the housing, a diffusive screen located within said opening, one or more light sources mounted within the housing adjacent the opposite side thereof so as to direct light normal to, and an acute angle to, the screen, the or each light source having a respective light obstructing element fixedly positioned between the screen and the or its respective light source, and the or each light obstructing element being arranged to permit more of the light from its associated source to pass through the peripheral area of the element than through the central area of the element.

Preferably, said element is formed of a translucent material.

Preferably, the peripheral area of said element is formed with uniformly distributed cut-away portions so that the element includes a broken, peripheral edge.

Conveniently, said light source includes an elongated fluorescent tube and said element extends along the length of the tube in a direction parallel with the axis of the tube, each longitudinally extending edge of the element including said cut-away portions.

Preferably, the internal surface of the housing is reflective.

Preferably, the apparatus includes a plurality, and more preferably two, of said light sources.

In the accompanying drawings, which illustrate one example of the invention, Figure 1 is a sectional view illustrating diagrammatically the overall apparatus Figure 2 is a sectional view showing the light source of the apparatus, and Figure 3 is a plan view showing part of the light obstructing element.

Referring to the drawings, the apparatus includes a housing in the form of a shallow, rectangular tray 11 having a length and width externally of 28 inches and 17 inches respectively, and internally of 21 inches and 16 inches respectively. The internal surface of the tray 11 is reflective and at its upper, open end the tray is closed by a diffusive screen 12 which is seated on inwardly directed shoulders 13 defined by the side walls of the tray at a distance of 2.75 inches from the internal base surface of the tray.

Mounted within the housing beneath tbe screen 12 are a pair of elongated, fluorescent tubes 14, each of which has a diameter of 0.625 inch and extends along the length of the tray 11 parallel with the screen 12 so that its external surface is spaced at a distance of 0.25 inch from the internal base surface of the tray and at a distance of 4.75 inches from a respective upstanding side wall of the tray. Each tube 14 conveniently has a power consumption of 13 watts and, as shown in Figure 1, the end, terminal caps 15 of each tube are arranged so as to lie below respective extensionsla which project inwardly from the free ends of the end walls respectively of the tray 11.

The extensions 1 lea are 2 inches in length and define with the shoulders 13, the seating for the screen 12.

Associated with each tube 14 is a light obstructing element in the form of an elongated strip 16 of translucent material which is located against the portion of the respective tube 14 presented to the screen 12 so as to extend parallel with the tube and the screen. Each strip 16 has a thickness of 0.125 inch and, as shown in Figure 3, is provided at each of its longitudinal edges with uniformly distributed cut-away portions in the form of triangular serrations 17.

Conveniently the serrations each define an included angle of 90" and are arranged three to every inch length of the strip so that the width of the strip varies between n maximum value of 1 inch and a minimum value of 0.75 inch. By virtue of the serrations 17, it will be seen that each strip 16 will, in use, permit more of the light from its respective tube 14 to pass through the peripheral area of the strip than through the central area of the strip.

With the apparatus described above, when the tubes 14 are energised, it is found that the illumination of the diffusive screen 12 is sufficiently uniform to permit viewing of X-ray plates through the screen. By way of contrast, to obtain a similar uniformity of illumination of the screen 12 when the light obstructing elements 16 are absent, it is found that the distance between the screen 12 and the internal base surface of the tray 11 must be increased to 4.5 inches, which of course results in an overall increase in the size of the apparatus.

While in the example described, the light obstructing element is a translucent element having triangular serrated longitudinal edges, there are many other forms which would allow more light to emerge through the peripheral edges than the central portion of the element. For example scallop-shaped cut-away portions and/or projections would achieve a similar result. Also, while a rectangular cross section of the light obstructing element is described, the crosssection could be in the form of a rectangular trapezium having its parallel sides parallel with the diffusive screen. In this case, there would be no need to provide cut away portions to obtain a substantially uniform pool of light on the diffusive screen.

While the light obstructing element has been described as translucent, it could be opaque and the light allowed to penetrate the element through appropriately shaped apertures therein, although a diffusive spread of light as provided by a translucent element is to be preferred.

WHAT WE CLAIM IS: 1. Transparency viewing apparatus including a housing having an opening at one side of the housing, a diffusive screen located within said opening, one or more light sources mounted within the housing adjacent the opposite side thereof so as to direct light normal to, and at an acute angle to, the screen, the or each light source having a respective light obstructing element fixedly positioned between the screen and the or its respective light source, and the or each light obstructing element being arranged to permit more of the light from its associated source to pass through the peripheral area of the element than through the central area of the element.

2. Apparatus as claimed in Claim 1, wherein said element is formed of a translucent material.

3. Apparatus as claimed in Claim 2, wherein the peripheral area of said element is formed with uniformly distributed cutaway portions so that the element includes a broken, peripheral edge.

4. Apparatus as claimed iP Claim 3, wherein said light source includes an elongated fluorescent tube and said element extends along the length of the tube in a direction parallel with the axis of the tube, each longitudinally extending edge of the element including said cut-away portions.

5. Apparatus as claimd in, any one of the preceding claims, wherein the internal surface of the housing is reflective.

6. Apparatus as claimed in any one of the preceding Claims and including a plurality of said light sources.

7. Apparatus as claimed .n any one of the preceding Claims and including twa of said light sources.

8. Transparency viewing apparatus of the kind specified comprising the combination and arrangement of parts substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. 0.125 inch and, as shown in Figure 3, is provided at each of its longitudinal edges with uniformly distributed cut-away portions in the form of triangular serrations 17. Conveniently the serrations each define an included angle of 90" and are arranged three to every inch length of the strip so that the width of the strip varies between n maximum value of 1 inch and a minimum value of 0.75 inch. By virtue of the serrations 17, it will be seen that each strip 16 will, in use, permit more of the light from its respective tube 14 to pass through the peripheral area of the strip than through the central area of the strip. With the apparatus described above, when the tubes 14 are energised, it is found that the illumination of the diffusive screen 12 is sufficiently uniform to permit viewing of X-ray plates through the screen. By way of contrast, to obtain a similar uniformity of illumination of the screen 12 when the light obstructing elements 16 are absent, it is found that the distance between the screen 12 and the internal base surface of the tray 11 must be increased to 4.5 inches, which of course results in an overall increase in the size of the apparatus. While in the example described, the light obstructing element is a translucent element having triangular serrated longitudinal edges, there are many other forms which would allow more light to emerge through the peripheral edges than the central portion of the element. For example scallop-shaped cut-away portions and/or projections would achieve a similar result. Also, while a rectangular cross section of the light obstructing element is described, the crosssection could be in the form of a rectangular trapezium having its parallel sides parallel with the diffusive screen. In this case, there would be no need to provide cut away portions to obtain a substantially uniform pool of light on the diffusive screen. While the light obstructing element has been described as translucent, it could be opaque and the light allowed to penetrate the element through appropriately shaped apertures therein, although a diffusive spread of light as provided by a translucent element is to be preferred. WHAT WE CLAIM IS:

1. Transparency viewing apparatus including a housing having an opening at one side of the housing, a diffusive screen located within said opening, one or more light sources mounted within the housing adjacent the opposite side thereof so as to direct light normal to, and at an acute angle to, the screen, the or each light source having a respective light obstructing element fixedly positioned between the screen and the or its respective light source, and the or each light obstructing element being arranged to permit more of the light from its associated source to pass through the peripheral area of the element than through the central area of the element.

2. Apparatus as claimed in Claim 1, wherein said element is formed of a translucent material.

3. Apparatus as claimed in Claim 2, wherein the peripheral area of said element is formed with uniformly distributed cutaway portions so that the element includes a broken, peripheral edge.

4. Apparatus as claimed iP Claim 3, wherein said light source includes an elongated fluorescent tube and said element extends along the length of the tube in a direction parallel with the axis of the tube, each longitudinally extending edge of the element including said cut-away portions.

5. Apparatus as claimd in, any one of the preceding claims, wherein the internal surface of the housing is reflective.

6. Apparatus as claimed in any one of the preceding Claims and including a plurality of said light sources.

7. Apparatus as claimed .n any one of the preceding Claims and including twa of said light sources.

8. Transparency viewing apparatus of the kind specified comprising the combination and arrangement of parts substantially as hereinbefore described with reference to and as shown in the accompanying drawings.