With respect to the evaluation of discomfort glare, the valuable works with a large number of observers involved have been reported since Nutting, P.G. in 1916. But in Japan up to now we have not made any fundamental research for such studies in spite of great demands from industry f or evaluation of glare.This study was planned as one of the research projects of the Research Committee of Recommended Levels of Illumination in the Illuminating Engineering Institute of Japan.For the criterion of glare evaluation, we adopted a brightness sensation, which was at the borderline. between comfort and discomfort, independently of a disability veiling brightness. We have termed this the BCD brightness according to the Luckiesh's expression.In this experiment, the aim was to examine a possibility of calculating the value of BCD brightness under similar conditions of Luckiesh's original experiment.The structure of apparatus for this preliminary experiment is shown in Figs. 1 and 2.This apparatus included a circular source having a diameter of 3.7 cm at middle of surrounding field at a distance of 100cm from the eyes, which is measured on the line of vision, and three steps of surrounding field brightness 1, 10, 100 footlamberts are prepared.In this test condition, the circular source subtended a solid angle of 0.0011 steradian. This circular source was able to change the brightness in the range of from 80 to 8, 000 footlambrts using a smoke wedge separately in surrounding brightness. The exposure time of this absolute method is 1 second following 5 seconds off period. Ths surrounding field was illuminated by two high-pressure fluorescent mercury lamps (400W).Results:Fifteen female subjects varying in age from 15 to 17 years were tested for this experiment. The BCD brightness value for each of the subjects is presented in Table 1. In this. experiment the background subtended field brightness of 10 footlamberts. The results show that the individual BCD brightness ranges from 1072 to 5920 footlamberts and that the arithmetic mean BCD brightness of the standard source, as named by Luckiesh, is 2903 footlamberts.With respect to the influence of field brightness, the effect of the adaptation brightness wass tested under the surrounding brightness of 1, 10 and 100 footlambrts. We found the average BCD brightness to be 1005, 2903 and 5283 footlamberts, respectively.It is interesting that in our investigation the relationship among the values of the threshold of BCD brightness at any luminance of surrounding field agreed with those of Luckiesh and Holladay, and of Nutting, but the values were higher than those of their results regardless of similar condition.It is questionable, whether these characteristics in our investigation are the result of incomplete condition of the experiment of not; it seems necessary for us to pursue more precise studies.We decided to manufacture an apparatus for more precise experiment instead of the present apparatus, especially for the illumination of adapting field and for exposure time of the brightness source.We shall report next time more precise results on these studies.