Weston Model 594 Photronic Cell

Weston 614, 615, 650, 703, 756, 819 & others

© Brooke Clarke 2008 - 2016

Background
594 Photronic Cell
    Photos
    Description
614 Foot-Candle Meter
615 Illumination Meter
617 Light Meter
650 Photronic Exposure Meter
703 Sight Light Meter
Weston 715 Master Light Meter
756 Foot Candle Meter
819 Cine Exposure Meter
Light brightness units
Reference
Patents
GE 8DW58Y Exposure Meter
Related
Links

Background

Light (Wiki: Electromagnetic Radiation) is part of the electromagnetic spectrum and broadly speaking covers the wavelength range of 40 nm to 1,000,000 nm.  This is from short Ultraviolet through long infrared (IR).  Only the narrow band of about 400 to 750 nm (blue to red) is what's called visible light (Wiki).  Near IR (Wiki) light (about 700 through 1200 nm) can be seen by using a digital camera that has the IR blocking filter removed.  This is sometimes called X-Ray since you can see through some clothes.  When measuring the light output from something that makes light there are two ways.  One is to measure the total power output at all light wavelengths and the other is to measure only the visible light output.  If the light is to be used by people seeing something with their eyes then the visible light output is the important thing.  Note that digital cameras have silicon imaging chips that can see near IR light, but they also have a filter that eliminates near IR light so that the overall response of the imaging chip comes close to human eye response so that color photos will look correct.

There are a number of ways that light can be converted into an electrical signal allowing it's brightness to be measured.  One of the key problems they face is to have a response that matches that of the human eye (Wiki: Luminosity, CIE 1931 color space).  If the spectral response of the sensor does not match that of the eye then the reading may be too high or too low.  When modern Silicon sensors are used to measure light something needs to be done to cut the IR response of the Silicon that's much more sensitive than the eye.  The  filtering that's used on Silicon sensors is a reasonable approximation, but not as good as the Weston 594 Photonic Cell with the Visible Correction (VISCOR) filter. 

Weston 594 Photronic Cell

I think the Weston 594 Photonic Cell is the basis of a number of specifications for visible light and they are still being made today by Huygen (the company is named after Christiana Huygens [Wiki]).  Which is triply fitting since the son of Edward Weston 1850-1936 (309 patents mostly relating to electric meters) named his son Edward Faraday Weston 1878-1971 in honor of Michael Faraday [Wiki].  The patents signed Edward Weston are the fathers and Edward F. Weston the son.  Although the "Weston" light meter was/is a standard of the photographic industry and popularized by Ansel Adams and Edward Weston the photographer used them it was made by Weston Electrical Instrument Co. and mostly due to Edward F. Weston.  That's three different people called Edward Weston.  Called a dry disk type photoelectric cell.

An ad in the Dec 1932 issue of Electrical World says that 14 months prior ( Oct. 1931) Weston started advertizing the Photronic cell (and relay).

See:Transactions of the I.E.S.:  New, Color Corrected Photronic® Cells for Accurate Light Measurements by Marlin E. Fogle (R&D Engineer at Weston Electrical Instrument Corp.).
Dr. H.P. Gage of Corning glass developed the blue-green glass filter specifically for the VISCOR filter to remove the excess red and near IR response. 
The other filter is yellow to remove the excess blue response.
Cites a prior article in the same Transactions of the I.E.S., but in XXVII, No. 9, pg 828-835 (1932).
Fig 2 shows the 614 and 756 Illumination Meters.

Photos

Weston Model 594
                  Photronic Cell
Weston Model 594
                  Photronic Cell
Weston Model
                  594 Photronic Cell

Weston 594
                  Photonic Cell



Description

Prior art Photoelectric Cells did not have a stable light to output conversion factor, they degraded over time so could no be used to make a light measuring instrument.

This is a Selenium based photo cell where each cell only generates a small voltage, but with strong current and so a number of these can be connected in series to get a useful current.  This version (called YY or Yellow Yellow (see the color dots in photo above) has an output of 46 to 58 micro amps at 20 foot candles with a 200 Ohm load.  The (output at 200 fc) / (output at 20 fc) >= 8.6.  The 200 Ohm load was used back in the vacuum tube days, but today a virtual short input amplifier will improve the linearity compared to what you would get with the 200 Ohm load.

There are different filters available for the 594 but I don't yet know which is on this one.

Weston 614 Foot-Candle Meter (Reflected Light Meter?)

The 614 and 615 light meters are very similar and I think they both use either the 594 cell or a version of it based on the wording in their description.
"Corrected to Visual Response" on meter face.

The photocell in both the 614 and 615 meters can be rotated up about 90 degrees so that you can hand hold the meter in your right hand using the strap while walking around a room and measure the light intensity falling on a horizontal surface (the photo cell surface should be parallel to the surface being measured.

The 614 does not need a battery.  It only contains the photocell and some wire wound resistors for the range switch.

mentioned in patent:  2050224 Projector for color motion pictures - filed Sep 5, 1933 - so in use then.

Still photographers typically use reflected light metering (Wiki: light meter), i.e. from the camera position looking at the subject.

When the pancake probe of a Bicron 50 radioactive Survey meter is placed on top of the photocell it reads 20,000 counts per minute.
But when the Bakelite (Wiki) lid is closed the reading drops to background count.
Weston 614 Foot Candle Meter
Weston
                      614 Foot Candle Meter
Weston 614 Foot-Candle Meter with photocell rotated up
Weston
                      614 Foot Candle Meter
Inside
Weston
                      614 Foot Candle Meter

Radioactivity measured using Bicron 50 Surveyor & PGM pancake probe.

The radioactivity is coming from the photocell and not other
parts of the 614.

When a sheet of copy paper is placed between the photocell
and the probe there is a slight drop in the count.
Without Paper  CPM = 20,500
Weston
                      614 Radioactivity
With Paper  CPM= 17,500 (varies from 17,000 to 20,000)
Weston
                      614 Radioactivity


When Aluminum foil folded twice (4 layers) is interposed
the Counts Per Minute drops slightly more than for paper.
Without Aluminum foil CPM = 20,500
Weston
                      614 Radioactivity
With 4 layers of Aluminum foil  CPM= 13,500
Weston
                      614 Radioactivity


When the Bakelite lid (3.9mm thick) is closed no radiation is sensed.

One theory is that they use thorium for refraction reduction and uranium for color filtering?
With Bakelite cover closed CPM = 0
Weston
                      614 Radioactivity



Weston 615 Illumination Meter (Incident Light Meter?)

The 615 meter uses a common 9 Volt battery and contains an op amp and associated precision metal film resistors.
The 615 has a white cap on the photocell.
"Corrected to Visual & Cosine Response" on meter face.

Movie photographers typically use incident light metering, i.e. the light meter is at the subject location and measures the light falling on the subject. The Sekonic movie light meter (Wiki) has a white hemisphere on a swivel mount and it is the brand I used with a Bolex H16 16mm camera (Wiki).

Since the Model 614 and 615 have sequential model numbers and one is for still photography and the other is for movie photography, they may be the first light meters intended to measure light for the purpose of exposing film.  But the table inside both models is for light for various tasks like reading, etc.

The geiger counter reading is only 4,000 counts per minute for this meter, much less than for the 614 above.  Probably because the white diffuser blocks the radiation.
With the Bakelite lid closed only background radiation is measured.

Weston 615 Foot Candle Meter
Weston
                      615 Foot Candle Meter

Under the yellow paper is says:
Weston
Schlumberger
Made in U.S.A.
Weston 615 Foot-Candle meter with photocell up and back off
Weston
                      615 Foot Candle Meter
Weston 615 Foot-Candle meter with back off showing 9V battery and zero and another adjustment pots.
Weston
                      615 Foot Candle Meter

Weston 617


Weston 7

One of the earliest photoelectric exposure meters and marked the introduction of the Weston film speed system (Wiki).
It wasn't till 1949 that the Weston exposure meters switched to the then new ASA system. 
Note:  The difference between the Weston film speed and the official ASA film speed was a difference of 1/3 stop.
I expect at that time it amounted to no difference and may have been done so that Weston could not claim to be the total basis for the ASA system.

Weston 650 Photronic Exposure Meter

In the late 1920s film speeds (Wiki) were not yet standardized between manufacturers, so each brand had their own system.

Weston 650 Photronic Exposure Meter
Patents shown on front:

1579849  see below
1779574 see below
1982406 see below
Weston 650 Photronic Exposure Meter Place for Emulsion Speeds
since films were not standardized.
Weston 650 Photronic Exposure Meter Weston Film Ratings Booklet


D97827 Photoelectric Exposure Meter, Edward F. Weston (Weston Electrical Instrument Corporation), Dec 10, 1935, Application September 12, 1935, Serial No. 58,536

Weston 703 Type -3 Sight Light Foot-Candles Meter 

About 1926 based on patents on meter face.  Note not intended for photographic exposure, but rather Illumination (Wiki) and Photometry (Wiki), Foot-candle (Wiki).

1579849 see below
1635595 see below
1661214 see below
2003919 see below



Weston
                      703 Sight Light Meter exposure
Back Cover Removed
Weston
                      703 Sight Light Meter exposure


Weston 715 Master Light Meter

This is very similar to a light meter I used decades ago.  I remember the hinged light baffle that also changed the meter scale.
Note in the photo where the baffle is opened the meter is reading the daylight in the room.


Weston 617 Master Light Meter
Weston 617 Master Light Meter Weston 617 Master Light Meter
Weston 617 Master Light Meter




Weston 756 Foot Candle Meter

Weston 756 Illumination Meter with VISCOR filtered Photronic cell


Weston 819 Cine Exposure Meter

Weston 819 Cine Exposure Meter

Weston 819 Cine Exposure Meter

Physically looks like the 650 still camera exposure meter, but the circular calculator and meter face are specific to movie cameras.
Dates:  Instruction book 1937
Weston Film Speed booklet: 1938
Kodak K135 Kodachrome Film sheet: 2-1957
Patent numbers: identical to the Weston 650 above

A letter to the first owner explains how to use it for still cameras.


Light brightness units

Lumens (Wiki) are a measure of the total visible light emitted by a source and it typically measured using an integrating sphere (Wiki).  For example the Lumen output of a LED would be the same after it's lens was filed off as it was with a narrow beam.  But the Foot-Candle reading with a narrow beam will be much higher than for the same LED after filing off the lens.  Some LEDs have their light output specified in MCD (milli candelas Wiki) and they get high numbers by using a very narrow beam lens.

On the other hand some flashlights advertize high lumen numbers, meaning they contain a bright LED, but do not have the optics to focus all that light into a beam to provide a high Candela value on the subject being illuminated.  The Xenide AEX25 1500 Lumen HID flashlight uses a High Intensity Discharge Xenon Short Arc lamp which allows designing an optical system that gets very close to all the light on the target, but an LED is far from a point source, i.e. it has a very directional light output pattern making it difficult to get all the light where you want it.

from Wiki Foot-Candle, Exposure Value,

Foot
Candle
Lux
(lumen/m2)
Exposure
Value (EV)

594


1
10.764


Sunny
Day
15220
163,840 16
163 ma
open
Shadow
950
10240 12
0.55 ma
Indoor
Art Gallery
60
640
8

Christmas
Tree Lights
4
40
4

?
0.23
2.5
0

Indoors Window Light



0.02 ma
Maglite 2 AA Flashlight



0.35 ma
594 Notes:
Sunny Day 13 Mar 2009 39 deg North into ma range of Fluke 87 DMM.
A photographic light meter that reads in EV can be used to measure Lux.  See Table 3 in the Wiki EV article
L [lx] = 2.5 x 2EV

Reference

Book:
The Photronic Photoelectric Cell, Monograph B-8, Weston Electrical Instrument Corp, Newark, NJ, 1935
Chapter 1 Historical
Barrier Layer Cells
1876 Adams & Day
1883 Fritts
1926 Lars O. Grondahl ( Union Switch & Signal Co)
1970135 Light Sensitive Apparatus, Aug 14, 1934, 136/255 ; 136/265; 250/214R - many prior patents for rectifiers
2089830 Light Sensitive Apparatus, Aug 10, 1937, 250/214SG ; 136/255; 136/265; 250/210; 250/214.1; 307/5; 361/173 - copper oxide w/ Large Bolt in Center
Chapter 2 Light Units
Chapter 3 Fundamental Concepts
Chapter 4 Some Practical Applications of the Photronic Cell
Chapter 5 Experiments
Chapter 6 Suggestions for Proper Instrument Use
Chapter 7 Bibliography

Patents

In the 1920s there was a lot of patent activity related to adding sound to moving pictures typically done using vacuum tube technology.  There was also a lot of work on transmitting images electrically, later called television, again typically using vacuum tube technology.   In both these applications speed of response was very important.  But for measuring light for photography or to determine the light needed for various industrial applications a light meter with a response matching the human eye was required.

1579849 Pointer for electrical measuring instruments, Edward F Weston (Weston Electrical Instr Corp), Apr 6, 1926, 116/330 - helical spring screwed onto pointer for balance
1635595 Electrical measuring instrument, E.F. Weston, et al (Weston Electrical Instrument Corporation), Jul 12, 1927, 324/151.00R, 324/156, 324/155 - meter movement
1661214 Zero corrector, Carpenter Grant (Weston Electrical Instr Corp), Mar 6, 1928, 116/291, 324/154.00R -
1779574 Direct-reading photometer, Samuel Wein (Radiovision Corp)Oct 28, 1930, 356/218, 429/111, 250/214.0SG, 315/55 - photocell + meter
1982406 Exposure meter, Ferdinand Tonnies Hans (), Nov 27, 1934, 396/293, 356/225, 250/214.1 -meter points to camera setting (speed or f/stop)
2003919 Meter, Canfield Earl L, Jun 4, 1935, 356/227 - Weston 703  (This patent and the ones above are related to the 703 meter)

2000642 Photoelectric Device, Anthony H. Lamb (Weston Electrical Instrument Co), May 7, 1935, 136/251 ; 136/244; 250/214.1; 257/42
This may be the patent for the Photonic Cells
Called by:
2699521 FILAMENT BAR CASING
2677715 OPTICAL-ELECTRICAL CONVERSION DEVICE COMPRISING A LIGHT-PERMEABLE METAL
2728809 METHOD OF MANUFACTURING PHOTO- ELECTRIC CELLS
2919353 SOLAR POWERED PORTABLE RADIO RECEIVER OR THE LIKE
3018377 PHOTOELECTRIC DEVICE
3036219 PASSIVE RADIATION PROXIMITY DETECTOR
3445686 SOLID STATE TRANSFORMER


2016469 Exposure Meter, Edward F. Weston (Weston Electrical Instrument Co), Oct 8, 1935, 356/225 ; 250/237R; 356/228 - cylindrical with variable iris
2041816 Light sensitive cell, Carpenter Arthur, Ross Ernest (United Res Corp), May 26, 1936, 338/19, 369/120, 338/199, 136/259 - variable resistance
                Citations:
                1940245  Light sensitive cell, Arthur W Carpenter (United Res Corp), Dec 19, 1933, 428/433, 136/264, 338/15 -
                                variable resistance  - mixtures of platinum, osmium and iridium, either with or without palladium
                1942958   Light-sensitive cell, Arthur W Carpenter (United Res Corp), Jan 9, 1934, 338/15, 136/256, 338/292, 338/309 - variable resistance       
                1948766 Light sensitive cell (mounting methods)
               
2203209 Exposure meter, Weston Edward F (Weston Electrical Instr Corp), Jun 4, 1940, 356/228, 235/64.7, 235/86 - knob moves belt with exposure values
2046665 Exposure meter, Weston Edward F (Weston Electrical Instr Corp), May 19, 1933, 356/225 - cylindrical
2058562 Light intensity self-adjusting camera, Albert Einstein, Gustav Bucky (), Oct 27, 1936, 396/213 - mentions "Weston Photronic"

2073790 Photographic exposure meter, Goodwin Jr William Nelson (Weston Electrical Instr Corp), Mar 16, 1937, 356/222, 235/64.7 - Model 617 Type 1
2088070 Photoelectric tube, Spencer Percy L (Raytheon Production Corp), Jul 27, 1937 - sensitive in red and near IR
                313/538, 252/181.4, 427/74, 445/11, 445/12, 427/124, 204/164, 445/13, 427/126.5
2105255 Exposure meter, Green Newton B, Joseph Mihalyi (Eastman Kodak Co), Jan 11, 1938, 235/88.00R, D16/238, 235/64.7, 356/228 -w/exposure calculating disk
2123670 Electrical measuring instrument, Weston Edward F (Weston Electrical Instr Corp), Jul 12, 1938, 356/226, 235/64.7 - Light Meter (filed: Aug 16, 1935)
                Compact square with light sensitive rectangle in meter face.
2123470 Control Device, Anthony H. Lamb (Weston Electrical Instrument Co), Jul 12 1938, 361/173 ; 250/206; 250/214AL; 250/229; 250/554; 315/159; 361/157 -
Street light control uses time clock to change sensitivity.  I.e. not turn lights on the morning at same brightness as they were turned off at night.
2244264 Photoelectric Cell, Louis J. Seitz Jr.  (Weston Electrical Instrument Co), Jun 3, 1941, 136/256 - This is an improvement on the Photronic Cell.
2320185 Photoelectric Cell, Anthony H. Lamb (Weston Electrical Instrument Co), May 25 1943, 136/256 ; 257/E31.13 -
             ridged surface so sensitivity is dependent on the direction of the incoming light. 
            Why? Ans: so that the included angle of light would match a normal 46 deg. camera lens. 
            See:  Ollinger's Light Meter page & patent 1982406
2403863 Photoelectric Cell, Anthony H. Lamb (Weston Electrical Instrument Co), Jul 9, 1946, 136/256 -
Method of making contact to the top transparent layer (talks about the GE units, but not by name).
2425250 Encased Electrical Device, Anthony H. Lamb (Weston Electrical Instrument Co), Aug 1947,
 250/239 ; 116/206; 174/14R; 174/50; 174/564; 312/31; 324/156; 55/385.1; 55/512; 73/29.02; 73/73; 96/108 -
Looks like Weston 703 Light meter.


2433566 Process for manufacturing photoelectric cells of the dry disk type, Anthony H Lamb (Weston Electrical Instr Corp), Dec 30, 1947, 136/256, 136/259, 257/42, 257/431, 257/658
                 May be for Photronic cells              
2606215 Encased and hermetically sealed photocell, Anthony H Lamb (Weston Electrical Instr Corp), Aug 5, 1952,
                136/259, 174/50.52, 228/124.6, 174/50.6, 174/50.54, 313/523, 174/564, 174/528
2629039 Selenium Cell and Process for Making Same, George H. Shoemaker (Weston Electrical Instrument Co), Feb 17 1953,
             338/15 ; 136/264; 257/42; 257/E21.07; 29/620; 427/123; 427/372.2; 427/383.7; 438/102; 438/486 -
            Simpler and better process to convert amorphous Selenium to crystalline form.  In glass tube.
            Calls:
                866462 Selenium Cell, W.J. Hammer, Sep 17 1907, 338/19 ; 114/21.2; 136/259; 250/214.1; 338/237 - cell acts as variable resistance
                2186085 Method of Making Selenium Rectifier Films, Samuel Weta (B-L Electric Mfg Co), Jan 9, 1940,
                 257/42 ; 148/270; 257/E21.071; 423/510; 427/76; 428/937; 428/938; 438/102; 438/84 -
                2196830 Photoelectric Cell, Clarence W. Hewlett (GE), Apr 9 1940, 136/255 ; 338/15 -
                2342278 Manufacturing Selenium Cells, H. Herrmann (Germany), Feb 22 1944,
                2364642 [typo in patent?]
                2413013 Method of Making Selenium Rectifiers, A. Von (Federal Telephone & Radio Corp), Dec 24, 1946,
                 438/102 ; 257/42; 257/658; 257/E21.071; 257/E21.072; 427/370 -
                2433401 Selenium Paste and a Method of Making it, Otto Saslaw (Intl Tel & Radio Corp), Dec 30, 1947, 438/102 ; 106/287.35; 252/62.3S; 257/E21.071 -
                2479301Selenium Rectifier, Wayne E. Blackburn (Westinghouse), Aug 16, 1949, 257/42 ; 252/62.3S; 257/E21.071; 257/E21.073; 257/E21.074 - blocking layer

2855567 Instrument adjuster element, Arthur D Clark, Anthon H Lamb (Daystrom Inc), Oct 7, 1958, 324/154.00R, 116/291 - zero adjuster


Patents that reference the Weston "Photronic Cell"

1963128 MEASURING APPARATUS - for sheet material
1940772 Oil TESTER
1990361 Exposure meter, BAILEY - cylindrical with iris
1993788 FIRE PREVENTION SYSTEM
1967583 TRANSPARENCY METER
1974522 COUNTING OP MICROSCOPIC BODIES-
2159181 ELECTRIC CONTROL SYSTEM
1938544 COLORIMETER
1940373 METHOD OF OIL TESTING
RE19255 METHOD OF TESTING Oil
2089859 SLOW ELECTROMAGNETIC RADIATION DEVICE
2068712 HIGH TEMPERATURE SLOW ELECTROMAGNETIC DEVICE
2051320 APPARATU for USING PHOTOELECTRIC - fatigue if exposed for an hour or so and wavelength dependent
2050486 AREA MEASURING MACHINE
2152645 PHOTOELECTRIC COLOR MEASURING AND ANALYZING APPARATUS
2054382 RADIATION PYROMETER DEVICE B
2111585 HEAD LAMP TESTING APPARATUS
2125639 APPARATUS FOR DETERMINING THE OPACITY OP PAPER AND OTHER MATERIALS
2149076 METHOD FOR THE MANUFACTURE OF CRYSTALLINE BODIES
2335655 CONTROL SYSTEM PANI S
2118082 COMPASS ALARM
2161004 PHOTOGRAPHIC DEVICE
2181841 MOTOR AND MOTOR-OPERATED APPARATUS
2114479 SHANNON AUTOMATIC STEERING COMPASS F
2184159 APPARATUS FOR MEASURING AREA O
2074641 MEASUREMENT OF HIGH TEMPERATURES
2171881 APPARATUS FOR MEASURING VISUAL EFFICIENCY
2102587 SOLAR NAVIGATOR
2177133 MEASURING INSTRUMENT
2239452 METHOD AND APPARATUS FOR PRODUCING SEMITRANSFARENT COATINGS
2230262 LIGHT POLARIZING SYSTEM
2232169 COLOBIMETEK IWUMS BL
2208147 PHOTOELECTEIC INCLINOMETER
RE22345 PROCESS FOR
2322225  CRANE ETAL
2298667 COLOR TEMPERATURE METER
2288807 AUTOMOBILE HEAD LAMP TESTING APPARATUS
2452038 PHOTOELECTRIC RADIO COMPASS TRAINER CONTROL
2454503 AUTOMATIC AURAL-VISUAL SIGNAL TRANSMITTER FOR AVIATION GROUND TRAINERS
2283190 FLIGHT INDICATOR
2323311 AUTOMATIC ALTITUDE CONTROL
2313733 LEVELING DEVICE
2333762 ANALYSIS
2397195 HEAT ABSORBING GLASS
2305442 BESSEMER CONVERTER BATH MEASURING
2892402 GRAVITY CONTROLLED MINE FIRING MECHANISM
2431899 PHOTROOSNTC CELL CIRCUIT
2501790 SILVERMAN
2489221 CRAFT LOCATING APPARATUS
2622221 FLUORESCENT DISCHARGE LAMP
2484809 COPY TABLE ASSEMBLY
2444442 PHOTO-ELECTRIC APPARATUS
2492148 AUTOMATIC NAVIGATING INSTRUMENT FOB CRAFT GUIDANCE
2467810 BARIUM MAGNESIUM LEAD SILICATE PHOSPHOR
2747455 DIFFERENTIAL REFRACTOMEIER
2780600 LEAD- AND MANGANESE-ACTIVATED CADMIUM-SODIUM FLUOROPHOSPHATE PHOSPHOR R
2899859 EXPOSURE METER FOR CATHODE-RAY TUBE PRESENTATION PHOTOGRAPHY
4380396 Method and apparatus for measuring the opacity of sheet material

GE Exposure meter Patents (from model 8DW58Y) i.e. a model 58

Design probably from the late 1920s, using "GE" film speeds.  They switched to ASA film ratings in 1946 (Wiki).
Note: this meter says on back "For film or plates use exposure index American Standard speed number".  Sold by the Army Exchange Service.


GE Exposure
                      meter model 8DW58Y

GE Exposure
                      meter model 8DW58Y

GE Exposure
                      meter model 8DW58Y
The front just pulls off - snaps back on
GE Exposure
                      meter model 8DW58Y



1779574 Direct-reading photometer,  Samuel Wein (Radiovision Corp), Oct 28, 1930, 356/218, 429/111, 250/214.0SG, 315/55 - simple & cheap
2073790 see above - Weston 617 Type 1
2096170 Light-sensitive device, Geisler Ottmar, Eisele Josef (Int Standard Electric Corp), Oct 19, 1937,
                 136/256, 428/668, 428/621, 428/686, 428/931, 257/431, 257/E21.75, 257/42, 428/657, 204/192.26, 338/15
                
cadmium (sulfide?) gold sensor
2196830 Photoelectric cell, Clarence W Hewlett (Gen Electric), Apr 9, 1940, 136/255, 338/15 - selenium
2209815 Photometer, Goss James H, Mccune Francis K (Gen Electric), Jul 30, 1940, 356/226 - inexpensive unit
2296670 Photoelectric cell, Clarence W Hewlett (Gen Electric), Sep 22, 1942, 136/259, 204/192.15, 136/264 - process for making a selinium photocell

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page created 22 May 2008.