USER MANUAL
White LED Light Meter
Model LT40
Additional User Manual Translations available at www.extech.com
Introduction
Congratulations on your purchase of the Extech LT40 LED Light Meter that measures light intensity
from white LED light sources. The LT40 can also measure light from fluorescent, metal halide, high‐
pressure sodium, and incandescent sources, for reference only (unspecified accuracy). The LT40
can measure light up to 40,000 Fc (400,000 Lux). This instrument is shipped fully tested and
calibrated and, with proper use, will provide years of reliable service. Please visit our website
(www.extech.com) to check for the latest version of this User Guide, Product Updates, and
Customer Support.
Features
Overload Indication: The LCD will show OL.
Low battery Indication.
Display Update Rate: 2.5 times per second.
Cosine Angle corrected.
Measures white LED light.
Measures the intensity of illumination in Lux or foot‐candles.
Data hold freezes displayed reading.
Maximum/Average/Minimum reading Hold.
Zero Calibration adjustment.
Auto power off with disable function.
Auto range.
Safety
Do not operate the meter in environments where the following are present: explosive gases
(or materials), combustible gases (or materials), steam, or dust.
Please replace the battery immediately when the low battery symbol appears on the LCD.
Do not touch the meter’s circuit board for any reason; static electricity or contamination
could damage the sensitive components.
For Indoor use only. This instrument was designed for pollution degree 2.
Operation Altitude: Up to 2000m (7000’).
2
LT40-en-GB_V3.0 10/17
Meter Description
1.
2.
3.
4.
Battery compartment and tripod mount are located on
rear of instrument
Photo detector (remove protective cover to expose sensor)
Display (LCD)
Control push‐buttons
Power Button: ON/OFF
Push‐Button Description
1.
2.
3.
4.
Lux/Fc units selector
Zero Calibration button
Maximum/Average/Minimum memory button
Data hold button
Operation
Power ON/OFF
Long press the Power button to power the meter. To power the meter OFF, short press the
Power button.
Taking Measurements
1. Switch the meter ON and remove the sensor’s protective cover to expose the light sensor
dome. The display should switch ON; if not, check that batteries are installed and fresh.
2. The meter measures the intensity of the light (illuminance) that strikes the sensor dome in
foot‐candles and Lux units (1 fc = 10.76 lux), displaying this measured value on its LCD.
3. Position the meter and light source so that the light strikes the sensor dome straight on
(perpendicular) with as little an angle as possible.
4. The meter’s display can show a value up to 9999. However, for readings that represent
measurements higher than this, the meter uses x10 or x100 feature. For example, to
represent a measurement of 11,000 fc the meter will display 1100 with the x10 indicator.
3
LT40-en-GB_V3.0 10/17
Auto Power OFF
To save battery life, the meter powers down automatically after approximately 12 minutes of
inactivity.
Enable/Disable Auto Power Off
While the meter is ON, long press the Power button to disable the Auto Power OFF utility (the
Clock symbol will switch OFF). To enable the Auto Power OFF utility, repeat this process.
LUX/FC Button
Press the LUX/FC button to toggle between Lux and FC (foot‐candles) measurement units.
MAX/MIN Button
The meter can record the maximum, minimum, and average readings as described below:
1. Short press the “MAX/MIN” button and the meter will begin to track the
maximum/average/minimum measurements; the “MAX” icon will display at the top of the
LCD window indicating that the meter is now showing the maximum reading. The reading
will not change until a higher reading is registered.
2. Press the “MAX/MIN” button again to switch from “MAX” to “AVG”, where the meter will
show the average measurement value. The “AVG” icon will be displayed above the displayed
value.
3. Press the “MAX/MIN” button again to change the mode from “AVG” to “MIN”, where the
meter will show the minimum value measured. The “MIN” icon will be displayed.
4. Press the “MAX/MIN” button again to switch from “MIN” back to “MAX”.
5. To exit this mode, hold the “MAX/MIN” button for at least 2 seconds. The MAX/AVG/MIN
icons should all be switched OFF when the unit returns to the normal operating mode.
HOLD Button
Press the HOLD button to freeze the current reading on the LCD. Press the HOLD button again to
release the reading. In the Data Hold mode, HOLD is displayed on the LCD.
Zero Calibration Procedure
1. Ensure that the protective cap is attached to the light sensor.
2. Power the meter and the LCD should display ‘0’.
3. Short press the “CAL ZERO” button to perform the zero adjustment (CAL will appear on the
display).
4. The CAL display will switch off when the calibration has been completed.
5. If the protective cap is not covering the sensor when the Zero calibration is started the LCD
display will read CAP. In this case, please cover the sensor with the cap and restart this
procedure.
4
LT40-en-GB_V3.0 10/17
Measurement Considerations and User Tips
For maximum accuracy allow the light being measured to fall directly on the sensor as
perpendicular as possible with a minimal angle of incidence.
When the meter is not in use, please keep the protective cap in place over the light sensor. This
will prolong the life of the sensor.
When the meter is to be stored for long periods, please remove the batteries and store them
separately. Batteries can leak and cause damage to the meter’s components.
Avoid areas of high temperature and humidity when using this instrument.
Battery Replacement and Maintenance
Cleaning and storage
1. The white plastic sensor dome should be cleaned with a damp cloth when necessary. Use
only a mild soap if needed. Do not use solvents, abrasives, or harsh detergents to clean the
dome.
2. Store the meter in an area with moderate temperature and relative humidity.
Battery Replacement
When the battery power decreases to a critical level, the low battery
”will appear on the LCD. Replace the 2 x 1.5V AAA
symbol “
batteries located in the rear battery compartment.
1. Press and hold the battery compartment lock button (see diagram).
1
2. Slide the battery compartment cover off in the direction of the
arrow.
2
Install two (2) 1.5V ‘AAA’ batteries observing correct polarity and close
the battery compartment. Ensure that the compartment cover is securely
fastened before using the meter.
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: Do not dispose of this instrument in household waste. The user is obligated to take
end‐of‐life devices to a designated collection point for the disposal of electrical and electronic
equipment.
5
LT40-en-GB_V3.0 10/17
聊聊、笑笑、闹闹
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
