GLOSSARY

Photometry
The measurement of light visible to the human eye.

Radiometry
The measurement of light within the total optical spectrum.

Color Temperature
The temperature of a blackbody whose radiation has the same visible color as that of a given non-blackbody radiator. Usually expressed in °k.

Foot-candle
Unit of incident illumination.

Foot-lambert
A unit of illumination emitted or diffusely reelected by a source. Two additional units are commonly used:
the lux (the metric unit of illuminance) and
the nit (the metric unit of luminance).
1 foot-candle = 10.76 lux
1 foot-lambert = 3.426 nits

Illuminance
The amount of luminous flux through a unit of surface area and is usually measured in foot-candles (lumens/ft²).

Inverse Square Law
The decrease of light intensity with increasing distance. Twice the distance, reduces the illumination to one-quarter.

Irradiance
The amount of radiant flux received by a unit of surface area and is usually measured in watts/cm^{2 *}.
^* Other units of irradiance such as uW/cm² and W/m² are also used extensively.

Lambert's Law
Describes the spatial characteristics of a perfectly diffusing surface which may be either emitting or reflecting light. The light emitted or accepted by such a surface decreases with angle (from perpendicular) according to the cosine of the angle.

Luminance
The amount of light emitted or scattered by a surface and is usually measured in  foot-lamberts.

Photopic
Spectral (color) sensitivity of the average human eye, predominantly peaked in the yellow-green region.

Steradian
A unit of area on the surface of a sphere equal to the radius squared. There are 12.6 steradians total area on a sphere.

Spatial
The directional characteristics of light in space.

Spectral
The distribution of light by wavelength within an electromagnetic spectrum.

Note that each radiometric unit has a photometric equivalent differing only in spectral response of the sensor. However, the units are not interchangeable.

PROBE CHARACTERISTICS

for probes: J6501 J6511 J6502/J6512 J6503 J6523 J6504 J6505

Source: Tektronix Catalog 1986

Attachments:

• US_Tek_J16_ProbeCharacteristics (71 KB)
• US_Tek_J16_SensorDiagram (34 KB)

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