A wide range, variable intensity light source of constant color characteristics has been developed for testing and calibrating photomultiplier tubes. A light attenuator first diffuses light from a constant source, then permits variable attenuation through a series of chambers and adjustable apertures

Snow, W. B.

English

NASA Technical Reports Server

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Light Output N 
.
May 1964
	 Brief 63-10424 
NASA TECH BRIEF 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Variable Light Source With a Million-To-One Intensity Ratio 
The problem: Development of a wide-range 
variable-intensity light source of constant color 
characteristics, that can be used for the testing and 
calibration of photo-multiplier tubes. 
The solution: A light attenuator having a 1,000,000 
to 1 intensity ratio that first diffuses light from a 
constant source, and then permits variable attenuation 
through a series of chambers and adjustable apertures. 
How it's done: A lightproof box is divided into 
several chambers, each containing one or more electric 
lamps. The device actually used consisted of three 
chambers, but a greater range can be obtained with 
the use of more chambers. Each of these chambers 
is painted white, and the rear and middle chambers 
have exit apertures leading to the chamber ahead. 
The output aperture is located in the forward cham-
ber on the wall , opposite the middle-chamber exit 
anerture. Each aperture is fitted with an iris which
can be varied to control the output from its respective 
chamber. Apertures are not aligned. In order to pro-
vide the necessary diffusion, a ground glass is placed 
between each light source and its respective exit 
aperture. 
Each chamber is inherently a high initial-loss device. 
Light intensity variation is achieved by manipulation 
of irises to admit light in measured amounts from one 
chamber to the next. Since the source lamps operate 
on constant voltage and current, color temperature 
output remains unchanged throughout the wide inten-
sity range. 
Operation of the light attenuator, as in the testing 
of photo-multiplier tubes, requires only the lighting 
of the required lamps and setting the openings of the 
apertures. In a typical application, the output of this 
device would go into the input of a phototube 
amplifier circuit, either directly, or first interrupted by 
a chopper.
/	 (continued overleal) 
This document was prepared under the sponsorship of the National 	 this document, or that the use of any information, apparatus, method, 
Aeronautics and S pace Administration. Neither the United States Govern-	 or process disclosed in this document may not infringe privately-owned 
ment, nor NASA, nor any person acting on behalf of NASA: A. Makes	 rights; or B. Assumes any liabilities with respect to the use of, or for 
any warranty or representation, express or implied, with respect to the	 damages resulting from the use of, any information, apparatus, method, 
accuracy, completeness, or usefulness of the information contained in 	 or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000073 2020-03-11T16:47:43+00:00Z
Notes 
This light attenuator can be easily and economi-
cally constructed. Its uses within NASA have been 
limited to specialized testing. 
For further information about this innovation in-
quiries may be directed to: 
Technology Utilization Officer 
Jet Propulsion Laboratory 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: B63-10424
Patent status: NASA encourages commercial use 
of this innovation. No patent action is contemplated. 
Source: Space Technology Laboratories, Inc.

under contract to Jet Propulsion Laboratory

(J PL-WOO-008)
is 
. 
Li 
Brief 63-10424


Variable light source with a million-to-one intensity ratio

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