. Light and lighting. ows should be properlydistributed over the walls of the class-rooms so that every desk shall be suffi-ciently lighted. The glass line of thewindow furthest from the teacher shouldbe on a line with the back of the last rowof 7 (a)—Ventilation. Although lighting from the left handis considered so important, ventilationdemands also the provision of a swingwindow as far from the lighting as possibleand near the ceiling. APPENDIX II. The Measurement of Solid Angles. As the solid angle plays such an im-portant part in daylight calculations, itmay be well to add a few
. Light and lighting. ows should be properlydistributed over the walls of the class-rooms so that every desk shall be suffi-ciently lighted. The glass line of thewindow furthest from the teacher shouldbe on a line with the back of the last rowof 7 (a)—Ventilation. Although lighting from the left handis considered so important, ventilationdemands also the provision of a swingwindow as far from the lighting as possibleand near the ceiling. APPENDIX II. The Measurement of Solid Angles. As the solid angle plays such an im-portant part in daylight calculations, itmay be well to add a few notes on themeasurempijt of such angles, and their usein photometry. This matter has beendealt with in an article in The Illumina-ting Engineer for January 1912, byProf. Silvanus P. Thompson. Solid angles are measured in terms ofthe area subtended at the point ofmeasurement divided by the square ofthe distance. The amount of solid anglewhich at unit distance radius is subtendedby unit area is known as one steradian. (or sterean), and the above formulamakes use of solid angles expressed interms of this unit. The whole solid angleof space around any point will be 47rsteradians. A window 6 feet high and3 feet wide at a distance of 30 feet sub-tends approximately 6X3 1 ,. (30? = 50 steradian- There is another method of measuringsolid angles which is sometimes con- 368 THE ILLUMINATING ENGINEER (jcly) v. nil nt and has been widely adopted byContinental authorities in researches nBchool lighting, namely, squaredegn i \ square degree is equal to tin-solid angle subtended by a Bquare eachnf whose sides subtends one angulardegree. Now on a sphere ol unit radiusthe length of 1 degree is obviously - I vu-Hence the area of one squan d<mapped out on the surface of such a Bphere will be (^)«=0-0003046unite of : t herefore one Bquare degn •? i-equal i 00003046 Bteradians. •• Fifty square degrees (Conns valuewhich occurs frequently in tin foregoingreport i is equal to about 0*015
Size: 1577px × 1584px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthori, bookcentury1900, bookdecade1900, bookpublisherlondon
