There are many organic and inorganic material have fluorescent naturaly, they are called “Proper Fluorescent”, but none or few fluorescent material are afforded fluorescent material, they are called “Second Fluorescent”, and these two materials are stimulated by Ultra-Violet Ray, especially near Ultra-Violet about 3650 Å.
They have wide application and important work applying these fluorescent reduction or many industrial and scientific techniqu.

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When the radiant energy emitte 1 from a disk source is measured by a radiationmeter located at any distance, it is important to have a knowledge of the relations between the radiant flux and the distance which are obtained from a structural dimension of the radiationmeter.
If the whole distance is devided into three regions to introduce the above-mentioned relations on a radiationmeter, a formula for the radiant flux 4, taking the distance as a variable is given for each region as follows:
(1)l<D≤l(R₀+r)/a+rΦ=πr²J-a²/l²+a²(φ, independent on the distance, D) (2) l(R₀+r)/a+r<D<l(R₀-r)/a-rΦ=2πJ∫^r₀Z(D, x)xdx=K(D)J(3) D≥l(R₀-r)/a-rΦ=πr²JR₀²/R₀²+D²In treating the case (2), a proposed approximation is suggested by the author in calculating the function φ, instead of solving theoretically.
A graph is shown here for the radiant flux incident to the thermopile of the radiationmeter, in case the radiancy of a circular disc source equals unity, taking its radius as a parameter, which was made in applying the above-mentioned approximation.
The use of this graph is desirable for practice where the radiancy and total emissivity of a circular disc source are measured by a radiationmeter.

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