401025 Datasheet, PDF (4/6 Pages) Extech Instruments Corporation. – Digital Light Meter

Selecting a Measurement Range
The meter has three measurement ranges (0-200, 0-2000, and 0-5000 Fc) and (0-2000, 0-
20000, and 0-50000) Lux). The proper range selection will produce the most accurate
reading. Always select the range that produces the maximum number of digits without
exceeding the maximum count for that particular range. For example, a reading of 1456 Fc
should be read on the 0 - 2000 range, not the 0-5000 range.
Zero procedure
The meter zero (display with no light input) may change with time. Occasional checking and
adjustment may be required.
1. Completely cover the sensor to block out any light.
2. Set the range switch to the lowest Lux or Fc range
3. Using a small screwdriver, adjust the “Zero” control for a zero display. The last digit
may change slightly. This is normal and does not affect the accuracy of the meter.
Analog Output
The analog output jacks on the front panel produce a 0.1mV DC per digit signal that can be
used for recording or datalogging purposes.
Lighting Type Correction Factors
The 401025 light meter is calibrated under a precise "Standard tungsten light source of
2856^OK". If the meter is to be used under a different type of light the correction factor of from
the table below should be applied to the readings obtained.
Mercury Lamp
Fluorescent Lamp
Daylight
Sodium
Metal Halide
x1.14
X0.92 to 1.12
x1.00
x1.22
x1.00
Replacing the Battery
When the left corner of the LCD display shows "LO BAT", it indicates the battery output is
below the design limit and the battery needs to be replaced. However, reliable measurement
can still be taken for another few hours before the tester becomes inaccurate.
1. Open the Battery Cover at the back of tester and remove the battery.
2. Replace with a 9V battery and install the cover.
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401025 Ver. 2.1 07/05