The duration of light emission from the fluorescent lamp is very long but its deterioration is so large that if we leave the lamps in a fluorescent lamp lighting installation to burn out, the illumina tion level decreases to some considerable extent and we must equip it with so many lamps. Now we have a new problem in lighting economics, which is solved in this paper.

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One of the anthers found the new deep red phosphor, magnesium arsenate, in 1949. By using this phosphor we developed “De Luxe” type fluorescent lamps: Daylight, Cool White, 3500°K White and Warm White.(Fig. 1-4) As this phosphor is excited by ultra violet light of shorter and longer wave-lengths as well as blue light, the lumen outputs of our “De Luxe” type lamps are larger thin other ones which apply other red phns phers and are 75% to 80% of those of the correspon ding standard colors.
The following three methods of the specification of color-rendering properties of fluorescent lamps were used by the authors.
1. Harrison's color contrast factor method
2. Azuma's method using C. I. E. and Munsell renotation color systems.
3. Our method using Hunter's a and β systems and Judd's equation
ΔE=f_gΔC=f_g√(k⁴√Y·ΔS)²+(Δ√Y)²
f_g=const, k=7, ΔS=√(Δα)²+(Δβ)².

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