®
Instruction Sheet
012-11060A
Light Level Sensor
PS-2177
*012-11060*
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*See the PASCO catalog or web site at www.pasco.com for compatible PASPORT interfaces and Data Acquisition Software..
Introduction
Photometry deals with the measurement of visible light as perceived by human eyes. The PASPORT Light Level
Sensor measures illuminance in lux. The readings of the sensor mimic the wavelength sensitivity of the human
eye, which is most sensitive in the green part of the spectrum (peaking at about 555 nanometers). This is
achieved with a green filter in the sensor.
In photometry, illuminance is the
luminous flux
incident on a surface,
per unit area
. In other words, it is the mea-
sure of the intensity of the incident light, wavelength-weighted to correlate with human brightness perception.
Illuminance is measured in lux, or lumens per square meter. Luminous flux, measured in lumens, is the perceived
power (energy per unit of time) of light. One lumen is defined as the luminous flux of light produced by a light
source that emits one candela of luminous intensity over a solid angle of one steradian. Luminous intensity, mea-
sured in candela, is the wavelength-weighted power emitted in a particular direction per unit solid angle. If a
light source emits one candela, a metric (SI) base unit, it emits monochromatic green light with a frequency of
540 terahertz (THz) that has a radiant energy of 1/683 watts per steradian in a given direction. A one-hundred
watt incandescent light bulb emits about 120 candela. A uniform one candela source emits 12.6 lumens.
Included Equipment
Part Number
Light Level Sensor
PS-2177
Recommended Items
PASPORT Extension Cable
PS-2500
PASCO Interface
Catalog or web site*
Data Acquisition Software
Catalog or web site*
Eight pin mini-
DIN connector
Light Dome
Light Level
Sensor
Range Select
Buttons
