Light and lighting . three-quarters of theobserved illumination, the remainderbeing due to the secondary reflection fromthe ceiling and to repeated reflection fromthe walls, and to the mercury lamps. On the other hand. Raanming that three-quarters of the illumination is directly due to the cove, this gives 15 randies per foot-run as a fair value for the a source of light, and from this and the observed value 22 we obtain -71 as thecoefficient of diffused reflection of thecove. \- an approximation, consider(platter of the theatre OABC, to Scale, the middle point being <». and AH being half t
Light and lighting . three-quarters of theobserved illumination, the remainderbeing due to the secondary reflection fromthe ceiling and to repeated reflection fromthe walls, and to the mercury lamps. On the other hand. Raanming that three-quarters of the illumination is directly due to the cove, this gives 15 randies per foot-run as a fair value for the a source of light, and from this and the observed value 22 we obtain -71 as thecoefficient of diffused reflection of thecove. \- an approximation, consider(platter of the theatre OABC, to Scale, the middle point being <». and AH being half the long side and BC half the shortside. Draw the diagonal P, and drawOD and OB to the middle points of A BC. Draw <;F at right-angleOD. This represents the side AB swung round to face 0. Similarly draw a line through F at right angles to 0E. line <;F BOales 27 2 ft. and the other ft. At 15 candles per foot-run Iare equivalent to Jos and ?! cat THE ILLUMINATING ENGINEER (may) 231. A view of the Lecture Theatre of the Institution of Civil Engineers, London. Theillumination is derived mainly from the white frieze lighted by concealed lights,and there aie also mercury vapour lamps above the glass in the central a knowledge of the dimensions of the room and the area and surface-brightness of the illuminated frieze it is possible to estimate the illuminationprovided at the level of the seats and Council table (Mr. A. P. Trotter). B 2 232 THE ILLUMINATING ENGINEER (may) The point at which the illumination Is tobe found is 20 ft. below the cove. From0 draw an arc OH of 20 ft. radius, anddraw OH at right-angles to OD. JoinDH, then DH, which scales 324 ft., isthe slant height from the point D onthe cove to point H 20 ft. below it, and
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