Color-matching properties on the basis of metameric gray object colors were derived for Planckian radiators and CIE standard daylight illuminants with different values of correlated color temperatures with respect to the reference illuminant D₆₅.
Then, color-matching properties of CIE daylight illuminants were compared with those of fluorescent lamps, which are different kinds of reconstituted fluorescent lamps with the same chromaticity as that of D₆₅ and four kinds of actual fluorescent lamps with high R_a values and with correlated color temperatures 4, 200 K, 5, 000 K and 5, 500 K.
The results confirmed following conclusions:
1) Adequateness of north skylight for color-matching work was estimated by following two reasons.
a) Pretty good stability of illuminance as compared with other directions of daylight, and
b) good color-matching properties of daylight illuminants irrespective of large variations in their spectral power distributions for different days of observations.
(2) In the case of the reference illuminant D₆₅., the reconstituted fluorescent lamp with the same
chromaticity as D₆₅. and with R_a=92.1 (the maximum R_a value is 94.6 for these reconstituted
fluorescent lamps) has better color-matching property than fluorescent lamps with high Ra
values (R_a=97-98) but with correlated color temperatures lower than 6, 500K.

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Generally, study of economical illumination is not considering productivity by lighting improvement, therefore, these studies are fear to digress from the actual conditions.
Relations of Illumination Levels E as exponential function and Productivity P introducing from psychometrics and econometrics in behavioral sciences, are followed.
P=klogE+α
where, k and α: coefficients
Coefficient k and α are indroduced from various seeing tasks
ksinθ+αcosθ=0Q
where, θ and OQ: coefficients
Generally, θ=70° and OQ=42 for various seeing tasks in Past experiments.
Economical illumination levels of industrial lighting are introduced
E (logE+123.5/k-3.77) =B/k₂
where, B: fixed charge (yen/day), k₂: lighting cost (yen/day).

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