ILLUMINATION REQUIRED BY THE HUMAN EYE

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B05171A000100020039-5
• Release Decision: RIPPUB
• Original Classification: S
• Document Page Count: 2
• Document Creation Date: December 28, 2016
• Document Release Date: April 18, 2003
• Sequence Number: 39
• Publication Date: April 5, 1968
• Content Type: MF

Approved For Release 2003/05/1 : Q- LT78BO5171AO00100020039-5
NPIC/TSSG/DED-1165-68
5 April 1968
MEMORANDUM FOR: Chief, Development Engineering Division, NPIC/TSSG
SUBJECT : Illumination Required by the Human Eye
1. The recently distributed "Human Engineering Design Guide by the
has proved quite valuable as a reference in evaluating
the illumination system for the High Precision Stereo Comparator.
2. The specifications state that the Stereo Comparator will
provide 0.2 stubs at the operators eye under most conditions. In ex-
treme cases such as looking at a step wedge and attempting to differen-
tiate between 2.9 and 3.0 density film at 200X magnification, the illumin-
ation level will automatically be reduced to 0.026 stilbs to prevent
damage to the film. Neither previously available reference material nor
the past experience of the DED personnel could provide information to the
effect that these illumination levels were adequate.
3. While reviewing the new Guide I found in Section 4 that
15 foot lamberts is adequate illumination level at the eye for young in-
terpreters and 25 foot Lamberts adequate for the general interpretation
population.
4. General Physics and Optics Books indicate that 1 stilb = 2919
foot Lamberts? Therefore, 0.2 stilbs is equal to 584 foot Lamberts and
0.026 stilbs == 90 foot Lamberts. Thus even at the worst condition the
interpreter will have three to four times as much light as is required
(90 f.l. as opposed to 15 or 25 f.l.).
5. This information then provided what I needed in setting up an
acceptable specification with the Contractor.
25X1
Distribution:
Orig - Addressee
2 - NPIC/TSSG/DED/R&DBII
TaSG[DE11
Declass Review by NIMA/DOD
Approved For Release 2003/05/14: CIA-RDP78B05171A000100020039-5
SECRET
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