403125 Datasheet, PDF (5/8 Pages) Extech Instruments Corporation. – Digital Light Meter

Operation
1. Set the function switch to the desired unit of measure; lux or fc.
2. Remove the light sensor cover.
3. Hold the sensor head steady or place it in a secure area and allow the sensor to collect
light. The light must encompass the entire sensor dome. Ensure that the user does not
cast a shadow on the sensor dome. The sensor is connected to the meter by a 4’
(1.5m) cable. While measuring, the sensor can be kept docked on the meter (as it is
shipped) or it may be disconnected and used remotely.
4. Read the illuminance value on the display. If the approximate magnitude of the light is
not known, step through the ranges using the RANGE button until a measurement is
displayed. If x10 appears on the LCD, the meter is in the 20,000 range and the reading
must be multiplied by 10. The OL (overload) icon appears if readings are out of range.
5. While taking a measurement, press the HOLD button to freeze a displayed reading.
Press HOLD again to release the displayed reading. The H icon will appear on the
display when the meter is in the HOLD mode.
6. If it is desired to know only the highest reading of a given measurement period, press
the PEAK button at the start of a measurement period. The PMAX display icon will
switch on in the PEAK mode and the display will only show the highest reading.
Momentarily press the PEAK button again to exit the PEAK mode.
7. Press and hold the PEAK button for seconds to activate the display backlight. Press
and hold the PEAK hold button again for 2 seconds to switch the backlighting off.
8. Cover the sensor when not in use.
Measurement Considerations
1. For best results, repeat measurements several times to ensure that the light source
has remained stable.
2. Avoid flexing the cable excessively at either end.
3. The Inverse Square Law: The law states that the illuminance E at a point on a surface
varies directly with the intensity I of a point source, and inversely for the square of the
distance d between the source and the point. If the surface at the point is perpendicular
to the direction of the incident light, the law is expressed as E = I / d².
4. Cosine Law: The law states that the illuminance on any surface varies with the cosine
of the angle of incidence. The angle of incidence θ is the angle of the surface plane
and the direction of the incident light. The inverse-square law and the cosine law can
be combined as follows: E = (I cos θ) / d².
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403125 V3.1 9/06