DescriptionPrior 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: Projector for color motion pictures - filed Sep 5, 1933 - so in use then.
Still photographers typically use reflected light metering (Wiki: ), i.e. from the camera position looking at the subject.
When the pancake probe of a radioactive Survey meter is placed on top of the photocell it reads 20,000 counts per minute.
But when the Bakelite () lid is closed the reading drops to background count.
Weston 614 Foot Candle Meter
Weston 614 Foot-Candle Meter with photocell rotated up
Radioactivity measured using & 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
With Paper CPM= 17,500 (varies from 17,000 to 20,000)
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
With 4 layers of Aluminum foil CPM= 13,500
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 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 () has a white hemisphere on a swivel mount and it is the brand I used with a Bolex H16 16mm camera ().
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.
Under the yellow paper is says:
Made in U.S.A.
Weston 615 Foot-Candle meter with back off showing 9V battery and zero and another adjustment pots.
One of the earliest photoelectric exposure meters and marked the introduction of the Weston film speed system ().
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 () were not yet standardized between manufacturers, so each brand had their own system.
Patents shown on front:
1579849 see 1779574 see
Place for Emulsion Speeds
since films were not standardized.
Weston Film Ratings Booklet
Photoelectric Exposure Meter, (), 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 () and Photometry (), Foot-candle ().
1635595 see 1661214 see
Back Cover Removed
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 756 Foot Candle Meter
Weston 756 Illumination Meter with VISCOR filtered Photronic cell
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
A letter to the first owner explains how to use it for still cameras.
Light brightness units
Lumens () are a measure of the total visible light emitted by a source and it typically measured using an integrating sphere (). For example the Lumen output of a 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 ) 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 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.
Indoors Window Light
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 article
L [lx] = 2.5 x 2EV
The Photronic Photoelectric Cell, Monograph B-8, Weston Electrical Instrument Corp, Newark, NJ, 1935
Chapter 1 Historical
Barrier Layer Cells
1876 Adams & Day
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 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
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.
Electrical measuring instrument, E.F. Weston, et al (), Jul 12, 1927, 324/151.00R, 324/156, 324/155 - meter movement
Zero corrector, (), Mar 6, 1928, 116/291, 324/154.00R -
Direct-reading photometer, ()Oct 28, 1930, 356/218, 429/111, 250/214.0SG, 315/55 - photocell + meter
Exposure meter, (), Nov 27, 1934, 396/293, 356/225, 250/214.1 -meter points to camera setting (speed or f/stop)
Meter, , Jun 4, 1935, 356/227 - Weston 703 (This patent and the ones above are related to the 703 meter)
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
Light sensitive cell, , (), May 26, 1936, 338/19, 369/120, 338/199, 136/259 - variable resistance
Light sensitive cell, (), Dec 19, 1933, 428/433, 136/264, 338/15 -
variable resistance - mixtures of platinum, osmium and iridium, either with or without palladium
Light-sensitive cell, (), Jan 9, 1934, 338/15, 136/256, 338/292, 338/309 - variable resistance
Light sensitive cell (mounting methods)
Exposure meter, (), Jun 4, 1940, 356/228, 235/64.7, 235/86 - knob moves belt with exposure values
Exposure meter, (), May 19, 1933, 356/225 - cylindrical
Light intensity self-adjusting camera, , (), Oct 27, 1936, 396/213 - mentions "Weston Photronic"
Photographic exposure meter, (), Mar 16, 1937, 356/222, 235/64.7 - Model 617 Type 1
Photoelectric tube, (), Jul 27, 1937 - sensitive in red and near IR
, , , , , , , ,
Exposure meter, , (), Jan 11, 1938, 235/88.00R, D16/238, 235/64.7, 356/228 -w/exposure calculating disk
Electrical measuring instrument, (), 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.
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: & patent
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).
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.
Process for manufacturing photoelectric cells of the dry disk type, (), Dec 30, 1947, 136/256, 136/259, 257/42, 257/431, 257/658
May be for Photronic cells
Encased and hermetically sealed photocell, (), Aug 5, 1952,
136/259, 174/50.52, 228/124.6, 174/50.6, 174/50.54, 313/523, 174/564, 174/528
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.
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 -
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 -
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, , (), Oct 7, 1958, 324/154.00R, 116/291 - zero adjuster
Patents that reference the Weston "Photronic Cell"1963128 - for sheet material
1990361 , BAILEY - cylindrical with iris
2051320 - fatigue if exposed for an hour or so and wavelength dependent
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 ().
Note: this meter says on back "For film or plates use exposure index American Standard speed number". Sold by the Army Exchange Service.
The front just pulls off - snaps back on
Direct-reading photometer, (), Oct 28, 1930, 356/218, 429/111, 250/214.0SG, 315/55 - simple & cheap
2073790 - Weston 617 Type 1
Light-sensitive device, , (), 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
Photoelectric cell, (), Apr 9, 1940, 136/255, 338/15 - selenium
Photometer, , (), Jul 30, 1940, 356/226 - inexpensive unit
Photoelectric cell, (), Sep 22, 1942, 136/259, 204/192.15, 136/264 - process for making a selinium photocell
An Integrating sphere () was used by Edison when testing his light bulbs. It collects all the light from a source and so removes any directional aspect so gives you a measure of the total light output. I've watched eBay for a used one that's small, but they are still thousands of dollars.
Amprobe (Meterman) LM631A Digital Light Meter
M-227 Signal Lamp Equipment SE-11 - Gun shaped flashlight, trigger, relay, IR Filter option
Monolight Optical Spectrum Analyzer
& Beseler PM1 Darkroom Color Analyzer
& Wollensak L3524D Direct Vision Spectroscope
& Ocean Optics HR2000 Spectrometer
PAS-6 Metascope IR Viewer & IR Source
Starlight Scope, Night Vision Sight, Individual Served Weapon
SDU-5/E Marker Distress Light
UAS-4 Infrared Surveillance System, AN/AAS-14 Infrared Detecting Set, MK-898/AAS-14A IR Optical Filter Kit
M18 IR Binocular
LinksBack to Brooke's , , , , , , page
page created 22 May 2008.