Illuminating Engineering Practice: Lectures on Illuminating Engineering Delivered at the University of Pennsylvania, Philadelphia, September 20 to 28, 1916

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McGraw-Hill Book Company, Incorporated, 1917 - 578 halaman
 

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Halaman 41 - Symbols. — In view of the fact that the symbols heretofore proposed by this committee conflict in some cases with symbols adopted for electric units by the International Electrotechnical Commission, it is proposed that where the possibility of any confusion exists in the use of electrical and photometrical symbols, an alternative system of symbols for photometrical quantities should be employed. These should be derived exclusively from the Greek alphabet, for instance: Luminous intensity r Luminous...
Halaman 36 - I, of a point source of light is the solid angular density of the luminous flux emitted by the source in the direction considered; or it is the flux per unit solid angle from that source. Defining equation: . da or, if the intensity is uniform, fwhere u> is the solid angle.
Halaman 35 - K,,,, over any range of wave-lengths, or for the whole visible spectrum of any source, is the ratio of the total luminous flux (in lumens) to the total radiant power (in ergs per second, but more commonly in watts).
Halaman 39 - Mean horizontal candle-power of a lamp, — the average candlepower in the horizontal plane passing through the luminous center of the lamp. It is here assumed that the lamp (or other light source) is mounted in the usual manner, or, as in the case of an incandescent lamp, with its axis of symmetry vertical.
Halaman 116 - When auxiliary devices are necessarily employed in circuit with a lamp, the input should be taken to include both that in the lamp and that in the auxiliary devices. For example, the watts lost in the ballast resistance of an arc lamp are properly chargeable to the lamp. 889 The Specific Consumption of an electric lamp is its watt consumption per lumen. " Watts per candle " is a term used commercially in connection with electric incandescent lamps, and denotes, watts per mean horizontal candle-power.
Halaman 195 - In perfect diffuse reflection, the flux is reflected from the surface in all directions, in accordance with Lambert's cosine law. In most practical cases, there is a superposition of regular and diffuse reflection.
Halaman 37 - Brightness, b, of an element of a luminous surface from a given position, is the luminous intensity per unit area of the surface projected on a plane perpendicular to the line of sight, and including only a surface of dimensions negligibly small in comparison with the distance to the observer. It is measured in candles per square centimeter of the projected area.
Halaman 37 - For most purposes, the millilambert (0.001 lambert) is the preferable practical unit. A perfectly diffusing surface emitting one lumen per square foot will have a brightness of 1.076 millilamberts.
Halaman 38 - Coefficient of diffuse reflection is the ratio of the luminous flux reflected diffusely to the total incident flux. Defining equation: Let m be the coefficient of reflection (regular or diffuse). Then, for any given portion of the surface, E' m"H
Halaman 36 - Phot." One millilumen per square centimeter (milliphot) is a practical derivative of the cgs. system. One foot-candle is one lumen per square foot and is equal to 1.0764 milliphots. The milliphot is recommended for scientific records.

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