illumination meter with quartz filter
Date: 1935-1945
Inventory Number: 2004-1-0394
Classification: Light Meter
Maker: Weston Electrical Instrument Corporation (founded 1888)
Owner: Lawrence Bogorad (1921 - 2003)
User: Biological Laboratories, Harvard University (founded 1932)
Cultural Region:
Place of Origin:
Dimensions:
11 × 21 × 17.5 cm (4 5/16 × 8 1/4 × 6 7/8 in.)
Accessories: original case; photoelectric probe; lead wires
DescriptionA Weston Illumination Meter, model 756, with a leather case with handle. The measurements are made in foot candles, a non-SI unit of measurement for illumination, defined as the amount of light that the inside surface of a sphere with a radius of 1 foot would receive if there were a point source of one candela in the center of the sphere. In other terms, it is equal to one lumen per square foot.
From the included information card on this instrument: "The instrument indicates the illumination in Foot Candles, based on the New Candle, on the surface of the light target, or lumens per square foot evenly distributed. It is provided with a filter which changes the color sensitivity of the photoelectric cells to match that of the human eye, and can therefore be used to measure tungsten light, fluorescent lights of various colors, etc., without correction."
The "New Candle" refered to here is what would later come to be the SI united of the candela. In 1946, what constituted a "candle" was standardized by the Commission Internationale de l'Éclairage (International Commission on Illumination). It was based on the illumination of a black body set at the freezing point of platinum
To use the instrument, the subject range is set by means of a selection switch, and the target is placed on or near the surface to be measured, with the photosensitive side parallel to the light rays. To measure maximum illumination, the photosensitive side should be placed perpendicular to the light rays.
To view another example of this object, please refer to object number 2003-1-0117 in this collection.
From the included information card on this instrument: "The instrument indicates the illumination in Foot Candles, based on the New Candle, on the surface of the light target, or lumens per square foot evenly distributed. It is provided with a filter which changes the color sensitivity of the photoelectric cells to match that of the human eye, and can therefore be used to measure tungsten light, fluorescent lights of various colors, etc., without correction."
The "New Candle" refered to here is what would later come to be the SI united of the candela. In 1946, what constituted a "candle" was standardized by the Commission Internationale de l'Éclairage (International Commission on Illumination). It was based on the illumination of a black body set at the freezing point of platinum
To use the instrument, the subject range is set by means of a selection switch, and the target is placed on or near the surface to be measured, with the photosensitive side parallel to the light rays. To measure maximum illumination, the photosensitive side should be placed perpendicular to the light rays.
To view another example of this object, please refer to object number 2003-1-0117 in this collection.
Signedon plaque: WESTON INSTRUMENTS, INC. / WESTON-NEWARK DIVISION / NEWARK, NEW JERSEY / ZERO CORRECTOR
Inscribedon scale: QUARTZ FILTER NO.3828 / FOOT-CANDLES / WESTON MODEL 756 SUNLIGHT ILLUMINATION METER / USE ONLY WITH TARGET BEARING SAME NUMBER AS METER
in paint pen on readout instrument : 68-020
on tape on sensor: Bogorad 582
in paint pen on readout instrument : 68-020
on tape on sensor: Bogorad 582
FunctionMeasures light illumination in foot-candles.
ProvenanceFrom the office of Prof. Lawrence Bogorad, Dept. of Molecular & Cellular Biology, Bio Labs 5100 by Sara Schechner, Spring 2004.