Cincpac File No.
A2-11/FF1-1(2)/
S64/(0536) |
UNITED STATES PACIFIC FLEET
U.S.S. PENNSYLVANIA, Flagship |
|
| CONFIDENTIAL |
Pearl Harbor, T. H.
April 12, 1941. |
PACIFIC FLEET CONFIDENTIAL NOTICE 3CN-41
| From: |
Commander-in-Chief, United States Pacific Fleet |
| To : |
PACIFIC FLEET |
| |
| Subject: |
Dim Illumination during Blackouts and on Board Ships under Darkened Conditions. |
| |
| Reference: |
(a) |
Director, Naval Research Laboratory, Anacostia, ltr. C-S66-9 RPB/vhw dated 18 March 1941. |
1. Reference (a) is quoted for information.
"1. Recent experiments completed at this laboratory and published information concerning visibility of illumination from various sources, as well as Intelligence reports from Great Britain, indicate that the use of colored lights for dim illumination is most deceptive. Blue lights of the same intensity as a weak white (yellowish) light at the source has three times the intensity of the white light at 1/2 mile. The blue light in itself is a relatively ineffective illuminant for the dark corners and passageways on board ship and is relatively very visible to a distant observer dark adapted.
2. The following is a resume of data collected by the laboratory from its own experiments and from published information:
(a) A point source of light of 1/10 candle may be observed at a height (range) of 1000 yards under favorable conditions.
(b) The momentary flare of a lighted match amounts to 10 to 20 foot candles and may be visible at 5 miles or more under best conditions.
(c) The light of a match burning steadily in quiet air gives 3 candles and might easily be visible at 2 miles.
(d) The glow from a puffed cigarette gives 0.02 candle and would be visible up to 500 yards.
3. The maximum permissible illumination in foot-candles on circular areas of diffuse reflectivity 30 percent is given in the following table. The illumination is the maximum which the area may have and still not be observed from a height (range) of 1000, 3000, and 10,000 feet.
TABLE I
CIRCULAR AREAS |
Height of
observer,
clear weather |
|
0.5 ft. |
|
3 ft. |
|
30 ft. |
|
300 ft. |
| 1000 ft. |
|
1.4 |
|
0.03 |
|
0.002 |
|
0.0004 |
| 3000 |
|
13 |
|
0.2 |
|
0.005 |
|
0.0006 |
| 10000 |
|
120 |
|
1.5 |
|
0.03 |
|
0.0013 |
4. The diffuse reflectivity of the present Navy gray paint is about 30 percent, and of grass, trees, etc. 4 to 6 percent. The illumination of a well lighted room is 10 foot candles and above, with the lowest illumination for reading 0.1 foot candle. The illumination of full moonlight is 0.02 foot candle, and of daylight 500 to 10000 foot candles.
5. This information is forwarded as a matter of interest to the addressees."
DISTRIBUTION:
List II, Case 2. O. X.
AA1, AAA1, ND11-14.
P. C. Crosley,
Flag Secretary. |
H. E. KIMMEL. |
USS Penn.-13^1-12-41-1,125.
|