168 TRANSACTIONS OF THE 
of the room. Hence variation in this case cannot be 
represented by a smooth curve. 
As is to be expected, the distribution of illumination 
intensity diminishes regularly to the far side of the uni- 
laterally lighted rooms. The ratio of diminition for suc- 
cessive rows, starting with the row nearest the window, 
is a constant, and found in this investigation to be about 
1.3, meaning that the intensity on a given row is 1.3 
times that on the next row farther on. The variation for 
a unilaterally lighted room is shown in fig. 2. This 
curve has the same characteristics as the curve plotted 
from the equation I,—I,/N where I, is the intensity on 
the row nearest the window, I, the intensity on any given 
row, N the number of the row, and k a constant, in this 
case 1.3. Hence, by knowing the daylight factor for the 
first row, and the value of k it is possible to obtain the 
amount of illumination for any row of desks at any hour 
of the day, for any season of the year and for any kind 
of a day, by merely measuring the outside intensity 
adjacent to the room considered. 
To illustrate: Let the daylight factor for the first 
row be 15% and k~—1.3. Suppose, now, on a certain 
day the outside illumination is found to be 300 foot can- 
dles. Then I,—45 foot candles. If there are six rows 
of desks, the intensity on the last row, I,—45/6'! °=4.38 
foot candles. 
Distribution is affected by the time of day. It was 
found from the average of a large number of readings 
that the illumination on the first row was about 114 
times as much in the afternoon as in the forenoon and 
about 3 times as much on the last row in the afternoon 
as in the forenoon. This seems to indicate that the after- 
noon sun gives a higher intensity than does the forenoon 
sun and that the afternoon light penetrates farther into 
the room. This conclusion is further borne out by a com- 
parison between the light intensities on the first and 
\ast rows for mornings and afternoons. In the morning 
iours, it was found that the intensity on the first row 
‘was more than four times as much as that on the last 
ale in the afternoon it was less than twice as 
much. 
