Spherical Photo-meter for Linear Light Source

Abstract

Measurement of the total luminous flux of linear light source by the integrating photometer rends to involve some errors due to unlike light distribution. The error of measurment can by discussed in terms of the coefficient of final illumination, K (θ, ψ) and relative sensitivity, Pm/Po. From the view point of proceeding coef f icinents, the author explains the following in this paper.(1) It is possible to divide the error due to presence of the screen into two components, i. e. screen error and shadow error.(2) The best position of the screen is 2/5 of radius from the spherical center.(3) In the interest of the relative sensitivity, it is better to locate the linear source in parallel than at the right angle with the screen.(4) The coefficient of relative sensitivity drops rapidly to about 80% of diameter, with more approaching to a spherical wall. Therefore, it is [desirable that the length of source is about 85% of diameter.(5) As f ar as the linear source is measured within the limit of Pm/Po≅1, the substitution for the linear source and the point source can be measured at the same accuracy as for the susbtitution for the point and point source.(6) It is certain that H. Korte's transmission screen is effective for avoiding the aforementioned screen error, but it is useful only in palliating the difference of the light distribution, the disposition of the source, etc.