Abstract
The human face has been taken up as one of the main visual targets and the provision of its brightness has been a theme. There are some studies with regard to the necessary luminance of the face. However, with lighting design there are many cases where it is difficult to deal with the luminance, therefore it is desirable to convert this to illuminance, which is easier to work with.
Before now, the face was assumed to be a perfect reflacting diffuser and a method whereby this was converted to vertical illuminance was employed.
From the results of experiments regarding human identification in residential areas, J.F. Caminada et al have concluded that the semi-cylindrical illuminance is more pertinent than vertical illuminance and hemispherical illuminance. From the results of experiments in a dark room, the author has concluded that we can provide for brightness of the face by semi-cylindrical illuminance under the condition where an excess of shadow does not occur.
In this paper, the author investigates the influence of shadow when converting luminance to illuminance in real environments (general indoors, underground passages, parks and residential areas at night), and found the following:
(1) Within these kinds of environments and without regard for the influence of shadows, the face can be assumed to be a perfect reflecting diffuser and converted by means of the formula.
Esc=π·Lf/ρ
where Esc: semi-cylindrical illuminance.
Lf: luminance of the human face
ρ: reflectance (ρ=0.3)
(2) Semi-cylindrical illuminance is more pertinent than vertical illuminance in real environments.