The Mari皿 e traffic system consists of hu 皿 an being， vessels and environment ． This study shows the physical characters of the visual environment which is the back − ground of the visual perception of the targets at sea for safety and for a good lookout in prevent − ing 皿 aritime traffic accidents ． Author shows three points ． The first is the illuminance at the place of fore inside of the nav − igation bridge． The second is the luminance at the view point 〔 the sky)about 2 degrees over ho − rizon ． The third is the luminance at the view point (the sea surface)about 2 degrees under ho − rizon ． All measurements were carried out through the windshield glasses of the navigation bridge ， The main results are as follows； 1．The illuminance at the place of fore i 皿 side of the navigation bridge is standardized by the sun ' s altitude ． The relation between illuminance at the navigation bridge and the sun ' s alti − tude is under ； 〔 Sun ' s Altitude in degree ｝ ＝ 〔 nluminance of approximate value in lux：1x) ： (more 10 degrees) ＝ 〔 1000-100001x) 〔 − 3 degrees) ＝ 〔 101x) 〔 10degrees ｝ ＝ (10001x) (− 6 degrees ｝ ＝ 口 1x) 〔 Odegree) ＝ (1001x) 〔 − 9 degrees) ＝ (0． 01-0． 11x) 2 ． The luminance at the view point 〔 the sky about 2 degrees over hQrizon)towards the sun ' s direction in case of fine weather and in summer is about 7 ， 000-27， 000 cd ／ ． This luminance can be shown by the approximate formula Y 一 a ／ X 十 b ｛ Y ： luminance in cd ／ ， X ： sun ' s altitude in degree ， a ： constant ＝ one million ， b：constant ＝− 5，000) ． 3． The luminance at the view point ｛ the sea surface about 2 degrees under horizon)to − wards the sun ' s direction in case of less than 30 degrees of sun ' s altitude has sun glitter ' s in − f！ uence which makes watch officers to prevent his visual perception ．
