Method of and assembly for measuring equivalent sphere illumination

A method of determining the amount of equivalent sphere illumination on an object as viewed from a selected viewing point, said method including (a) positioning a specific object including a flat surface having a darker colored symbol thereon in a lighted first area, (b) selecting a viewing point and orienting said object relative to said point such that, at said point, the flat surface of said object is viewed at an acute angle to a line normal to said surface, (c) at said viewing point, viewing said surface through adjustable light filtering means, (d) adjusting said light filtering means to a position which will provide threshold visibility of said symbol, as viewed from said viewing point and causing the luminance of said flat surface at least to appear unfiltered as viewed through said adjusted filtering means from said viewing point regardless of the adjusted position of said filtering means, (e) positioning a reference object including a flat surface having a symbol thereon in a second area said second area being partially defined by a hemispherical surface which substantially uniformly diffusely reflects light directed thereon, (f) orienting said reference object relative to said selected viewing point such that, at said point, the flat surface of said reference object is viewed at an acute angle to a line normal to said last-mentioned surface, said last-mentioned angle being substantially identical to the angle at which said specific object is in view, (g) illuminating said reference object with sphere illumination, (h)with said light filtering means in said adjusted position, viewing said reference object through said filtering means from said viewing point, (i) varying the intensity of sphere illumination on said reference object until the visibility of the symbol on said reference object, as viewed from said viewing point through said light filtering means, is substantially equal to the threshold visibility of the symbol on said specific object as viewed from said viewing point through said filtering means and causing the luminance of the flat surface of said reference object at least to appear unfiltered as viewed through said adjusted filtering means from said viewing point, and (j) thereafter measuring the intensity of sphere illumination, the improvement comprising:

• a. using a single object including a flat surface having a darker colored symbol thereon as both said specific object and said reference object;
• and
• b. moving said single object from said first area to said second area after said step of adjusting said light filtering means.

An assembly for determining the amount of equivalent sphere illumination on a task, said assembly including (a) means for supporting said task and contrasting colored given reference in a lighted area, (b) a substantially closed housing including means for supporting a task and a contrasting colored reference therein, (c) means for illuminating said task and said reference within said housing with sphere illumination, (d) means for adjusting the intensity of sphere illumination on said task and reference within said housing, (e) adjustable light filtering means, (f) means for simultaneously viewing said task and reference in said lighted area through said light filtering means and for simultaneously viewing said task and reference in said housing through said light filtering means, whereby the visibility of said task, as viewed through said filtering means, can be altered by adjusting said light filtering means, (g) means for making the luminance of said reference at least appear unfiltered, as viewed through said filtering means, regardless of changes in visibility of said task, and (h) means for measuring the intensity of sphere illumination on said task and reference in said housing, the improvement comprising:

• means for moving a single task and contrasting colored reference from said supporting means in said lighted area to said supporting means in said housing, said single task and reference being used as both said task and reference in said lighted area and said task and reference in said housing.

An assembly for determining the amount of equivalent sphere illumination on a task, said assembly including (a) means for supporting said task and a contrasting colored reference in a lighted area, (b) a substantially closed housing including (i) an internal hemispherical surface which substantially uniformly diffusely reflects light directed thereon, and (ii) an internal flat surface capable of passing light therethrough and adpated to support a task and contrasting colored second reference, (c) means providing light through said flat surface and into said housing for illuminating said task and reference within said housing with sphere illumination, (d) means for varying the light passing through said flat surface and into said housing whereby to vary the intensity of sphere illumination of said task and reference within said housing, (e) an optical device having opposite first and second surfaces, said device being capable of passing variable amounts of light therethrough from said first surface to said second surface along a predetermined path and being capable of reflecting off of said second surface at least some light which is directed onto said second surface, (f) means for supporting said optical device in a predetermined orientation, (g) means for viewing simultaneously said task and reference in said lighted area from a predetermined viewing point through said optical device and for alternatively viewing simultaneously said task and reference in said housing from said viewing point through said optical device, whereby the visibility of said task, as viewed through said device from said viewing point, can be altered by varying the amount of light passing through said device from said first surface to said second surface, (h) means for making the luminance of said reference at least appear unfiltered, as viewed through said optical device, regardless of the changes in visibility of said tasks, (i) means for measuring the intensity of sphere illumination on said second task and second reference, the improvement comprising:

• means for moving a single task and contrasting colored reference from said supporting means in said lighted area to said supporting means in said housing, said single task and reference being used as both said task and reference in said lighted area and said task and reference in said housing.