Most of Japanese living rooms adopt a general lighting system with a suspended luminaire at the center of a room. A rational design of their lighting must be based on a prediction of the luminous emittance of the room surface.In order to predict the horizontal illuminance distributions on the floor or a horizontal plane 40 cm above the floor in a room (2.7m ×2.7m×2.4 m), we made a calculation of interflections using the light distributions of the luminaire.
In this case the considered square room was replaced by a cylinder one which has the same floor area and height as those of the square room so that the shape factors and the initial luminous emittances might be easily calcualted.
However, to apply this treatment in practice, it is necessary to know how the results obtained from the cylinder approximation agree with those obtained from the square room.
To study this problem the square room and the cylinder one were divided into 18 and 9 surface elements respectively and the following linear simultaneous equations were solved by using a digital computer.(Bendix G-15).
L_i=L_oi+ρ_i nΣ(j=1) F_ijL_j
where F_ij=1/πA_i∫A_i∫A_jcosθ_icosθ_j/rij²dA_idA_j
ρ_i=reflectance of an element i,
L_oi=inital luminous emittance of an element i,
and L_i=final luminous emittance of element i,
When the calculated results of interflections in the cylinder room were compared with those of the square room, the former showed lower values than the latter because of self-interflections being neglected in the reentrant surface elements.It, however, became clear that those two results were in exceedingly good agreement when self-interflections in the reentrant surfaces were taken into account.
We also measured the horizontal illuminance distributions on the floor and on a horizontal plane 40cm above the floor in a model room to check the reliability of our calcuation. The experimental results showed good agrement with those of calculation within the experimental errors.

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The design of the reflecting layer that is the first step in the production of ceramic electroluminescent lamps is one of the important factors deciding the characteristic of these lamps.
Two important factors for the design of the reflecting layer are dielectric concentration and layer thickness.
Theoretical concentration and thickness will be geometrically and electrically calculated. In this experimentation, titanate oxide is applied as the dielectric.
Dielectric concentration and layer thickness will depend on the relations between the concentration of titanate oxide and the electric current, between the concentration of titanate oxide and the impedance of the reflecting layer, and between the impedance of the reflecting layer and the brightiness or the efficiency of the electroluminescent lamp.
The impedance of a reflecting layer will increase in proportion to its thickness. The interaction between binder and titanate oxide has considerable influence on the relation between the rate of increase and the concentration.
The equivalent circuit of the electroluminescent lamp will give the impedance of the reflecting layer, and therefrom the relation between layer thickness and brightness will also be obtained.

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