General Tools and Instruments DLM204 - Manual (Page 3)

The meter displays measured light intensity in either of two
units: lux and foot-candles. The lux is the standard
international unit of illuminance, or how much luminous flux
is spread over a given area. One can think of luminous flux as
a measure of the total amount of visible light present, and
illuminance as a measure of the intensity of illumination on a
surface. A given amount of light will illuminate a surface more
dimly if it is spread over a larger area, so illuminance is
inversely proportional to area.
The standard international unit of luminous flux is the lumen,
and one lux is equal to one lumen/m
2 . For perspective on lux
readings from the natural world, a moonless clear night sky
has an illuminance of about 0.002 lux, while direct sunlight
has an illuminance of 30,000 to 130,000 lux.
The foot-candle (or lumen per square foot) is a non-standard
unit of illuminance. Like the Btu, it is mainly in common use
only in the U.S., particularly in construction-related
engineering and building codes.
Lux and foot-candles are different units of the same quantity.
One foot-candle (ft-cd) = 10.764 lux, and 1 lux = 0.0929 ft-cd.
The DLM204 has a 2 in. diagonal LCD with 1 in. high digits.
The meter is powered by a “9V” battery (included in the
package).
KEY FEATURES
• Readings displayed in lux or foot-candles
• Choice of four ranges for each unit
• Large 2000 count LCD
• Uses cosine angular correction, silicon photodiode and
filter to approximate relative spectral response curve
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