FOR IMMEDIATE RELEASE:                  Linda Joy
May 31, 1994                            (301) 975-4403

                                        TN-5979


              NIST'S NEW 'ELECTRONIC EYE' IMPROVES

                 ACCURACY FOR LIGHTING INDUSTRY


     In colonial times, lamp makers relied on whale oil-based
candles as a standard measure of light.  Today, a new "electronic
eye" developed at the National Institute of Standards and
Technology is giving the lighting industry its most accurate
measure of brightness ever.

     The new electronic eye is twice as accurate as the lighting
standard it replaces, explains NIST physicist Chris Cromer.
Scientists now are using the electronic eye to maintain the
candela, the international base unit for measuring light.  The
electronic eye, a photometer with a green filter, silicon
photodiode and an electronic circuit for signal processing, has
an aperture that works much the same way as the human iris.

     Technology has come a long way since the time of the whale
oil candle standard, and so has the demand for precise and
accurate lighting.  For example, lighting in cockpits and
dashboards must be at specific brightness levels for safety
reasons.  Proper lighting is also important for accurate color
perception.  Even federal grain inspection programs carry
specific lighting requirements.

     This new candela standard will help the lighting industry
meet new light bulb labeling requirements for brightness, energy
efficiency and color rendering.  It also will help ensure proper
illumination for vehicle control displays.

     "NIST's electronic eye is a detector which mimics the human
eye," Cromer says. "It's more sensitive in the green region of
visible light, just as the eye is."

     Using a detector as the candela standard has advantages over
previous methods, which were based on a light source, Cromer
explains.  The electronic eye replaces a multistep method based
on radiation from a black surface at the melting point of gold.

     The previous system used standard candela lamps as primary
reference standards.  Manufacturers could purchase these lamps
from NIST for calibrating their own products.  However, all the
intermediate steps in developing the standard lamps increased the
uncertainty of their calibration.  The brightness of the standard
lamps would drift slightly over the life of the lamp, Cromer
explains. 

     With the electronic eye, NIST has shifted from a light
source to a light detector as a primary standard.  Although
manufacturers can still purchase standard bulbs from NIST, they
can now send their own detectors to NIST for on-site calibration. 
NIST has eight standard detectors that are used to calibrate
detectors for the lighting industry. 

     The new method of calibrating detectors offers lighting
manufacturers a more direct comparison to NIST's primary lighting
standard.  The NIST device's stability fluctuates by no more than
0.1 percent per year, Cromer says. 

     The candela is one of the international base units of
measure maintained in NIST's Physics Laboratory.  The laboratory
also maintain standards for the second and the kelvin.

     As a non-regulatory agency of the Commerce Department's
Technology Administration, NIST promotes U.S. economic growth by
working with industry to develop and apply technology,
measurements and standards.

                              -30-

Note to editors: Black and white photos and color slides of the
new electronic eye are available upon request from Linda Joy at
(301) 975-4403.