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Model 401025
Digital Light Meter
USER MANUAL
Additional User Manual Translations available at
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Introduction
Congratulations on your purchase of the Extech Digital Light Meter. This device is shipped fully tested
and calibrated and, with proper use, will provide years of reliable service. Please visit our website
check for the latest version of this User Guide, Product Updates, and Customer
Support.
Meter Description
1. LCD Display
2. Data Hold Switch
3. Power Off/Range Switch
4. Analog Output Terminal
5. Battery Compartment (rear)
6. LUX/Fc Switch & Response Switch
7. Light Sensor
8. Zero adjust
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Operation
1. Select Units (Lux or Ft-candle) and the Response Time (Fast/Slow) using the slide switch. Typical
selection is Slow and Fc using the gray lettering.
2. Select the maximum range using the Range Switch.
3. Hold the Light Sensor so that the sensor faces the light source to be measured.
4. The display will indicate measured values. Use a range display multiplier if on the Lux 20,000 and
50,000 ranges or on the Fc 5000 range (see notes below).
5. To hold (freeze) a measurement, slide the Data Hold Switch to the Hold position. The reading will
freeze in the display until the Data Hold Switch is released.
Note 1: An Over Range indication is a display of "1__ ". If this occurs, switch to a higher range.
Note 2: For measurements made on the Fc 5000 range, the displayed reading must be multiplied by
Note 3: For measurements made on the Lux 20000 or 50000 ranges the displayed reading must be
Note 4: The meter will indicate values above the maximum ranges. The accuracy of these
10.
multiplied by 10 and 100 respectively.
measurements is unknown.
Range Display Multipliers
Range Units Multiplier
200 Fc Direct reading
2000 Fc & Lux Direct reading
5000 Fc Reading x10
20,000 Lux Reading x10
50,000 Lux Reading x100
Example: If a measurement on the 5000 Fc range displays 350 the actual measured value is:
350 x 10 = 3500 Fc.
Lux
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Selecting a Measurement Range
The meter has three measurement ranges for each unit of measure (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 2856OK. 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
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Replacing the Battery
(see range table
When the left corner of the LCD display shows LO BAT the battery output is below the design limit and
the battery needs to be replaced. However, reliable measurement can still be taken for several hours
before the tester becomes inaccurate or switches off.
1. Open the Battery Cover at the back of the tester and remove the old battery.
2. Replace with a new 9V battery and install the cover securely.
Never dispose of used batteries or rechargeable batteries in household waste.
As consumers, users are legally required to take used batteries to appropriate
collection sites, the retail store where the batteries were purchased, or wherever
batteries are sold.
Disposal:
life devices to a designated collection point for the disposal of electrical and electronic equipment.
Do not dispose of this instrument in household waste. The user is obligated to take end-of-
Specifications
General Specifications
Display 13mm (0.5") LCD (Liquid Crystal Display)
Measurement types Lux, Ft-candles (Fc)
Ranges
below)
Sensor Exclusive photo diode & color correction filter, spectrum
Zero Adjust Manual adjustment
Sampling Time Approx. 0.4 seconds
Response Time Fast: 0.4 seconds; Slow: 2 seconds
Over input indication Indication of "1__"
Analog Output 0.1 mV/1 digit (maximum output: 200mV)
Operating Temperature 0OC to 50OC (32OF to 122OF)
Operating Humidity Less than 80% RH
Power Supply 9V DC battery
Power Current Approx. 2 mA DC
Weight 220 g (0.52 lbs.)
Dimensions Main instrument: 163 x 70 x 30 mm (6.4 x 2.8 x
Optional Accessories Vinyl pouch carrying case (Part Number 409996)
Lux: 0 to 50,000 Lux in 3 ranges
Foot-candles: 0-5,000 Fc in 3 ranges
designed to meet C. I. E.
Sensor Probe: 85 x 55 x 12 mm (3.2 x 2.2 x
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Range Specifications
300 400 500 600 700 800
Lux
Range In-range Display Resolution Accuracy (FS)
2,000 Lux 0-1,999 Lux 1 Lux ± (5% + 2digits)
20,000 Lux 2,000-19,990 Lux 10 Lux ± (5 % + 2digits)
50,000 Lux 20,000-50,000 Lux 100 Lux ±(5 % + 2digits)
Foot-candle (Fc)
Range In-range Display Resolution Accuracy (FS)
200 Fc 0-199.9 Fc 0.1 Fc ± (5% + 2digits)
2,000 Fc 200-1,999 Fc 1 Fc ± (5% + 2digits)
5,000 Fc 2,000-5,000 Fc 10 Fc ± (5% + 2digits)
Frequency Spectrum
1
0.8
0.6
0.4
0.2
0
Wavelength (nm)
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Appendix A - Typical Light Levels
Factories
Home
Office
Restaurant
Store
Hospital
Lux Foot
Candles
Lux Foot
Candles
20-75 2-7 Emergency Stairs,
75-150 7-15 Exit/Entrance Passages 150-200 15-20 Recreational
150-300 15-30 Packing Work 200-300 20-30 Drawing Room,
300-750 30-75 Visual Work: Production
750-1,500 75-150 Typesetting: Inspection
1,5003,000
75-100 7-10 Indoor Emergency Stairs 75-150 7-15 Corridor Stairs
100-200 10-20 Corridor Stairs 150-300 15-30 Entrance, Wash
200-750 20-75 Conference, Reception
750-1,500 75-150 Clerical Work 750-1,500 75-150 Show Window
1,5002,000
75-150 7-15 Indoors 30-75 3-7 Emergency Stairs
150-200 15-20 Corridor/Stairs 75-100 7-10 Stairs
200-300 20-30 Reception 100-150 10-15 Sick Room,
300-500 30-50 Display Stand 150-200 15-20 Waiting Room
500-750 50-75 Elevator 200-750 20-75 Medical Exam Room
750-1,500 75-150 Show Window, Packing
1,5003,000
150-300 Electronic Assembly,
150-2000 Typing, Drafting
150-300 Storefront, Show Window 5,000-
Warehouse
Line
Work
Drafting
Room
Table
100-150 10-15 Washing
Activities
300-500 30-50 Makeup
500-1,500 50-150 Reading, Study
1,0002,000
300-750 30-75 Cooking/Dining
750-1,500 75-150 Operating Room
10,000
100-200 Sewing
500-1000 Eye Inspection
Table
Room
Room
Warehouse
Appendix B - Common Terms and Conversion Factors
Illuminance (Visible Flux Density)
Luminance (Visible Flux Density per Solid Angle)
Luminous Intensity (Visible Flux per Solid Angle) 1 lm/sr = 1 candella
Luminous Flux ( Visible Flux) 1 lumen (lm) =
1 lm/m2=
1 lm/m2/sr = 1 candela/m
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All rights reserved including the right of reproduction in whole or in part in any form
ISO-9001 Certified
1 lux (lx)
10-4lm/cm
10-4phot (ph)
9.290 x 10-2lm/ft
9.290 x 10-2foot-candles
1.464 x 10-3watts @ 555 nm
2
2
2
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