LI-COR LI-250 User manual

®
LI-250
LI-250
Light Meter
Light Meter
LI-COR, inc. ●Environmental Division
4421 Superior Street ●P.O. Box 4425 ●Lincoln, Nebraska 68504
Phone: [phone] ●FAX: [phone]
Toll-free 1-800-447-3576 (U.S. & Canada)
E-mail: [e-mail]
Internet: http://www.licor.com
®
Instruction 
Manual

LI-250
Light Meter
Instruction Manual
Publication Number 9604-114
April, 1996
®
LI-COR, Inc.
Environmental Division
4421 Superior Street
P.O. Box 4425
Lincoln, Nebraska 68504
Phone: [phone]
FAX: [phone]
Toll-free 1-800-447-3576 (U.S. & Canada)
e-mail: [email protected]
Internet: http://www.licor.com

ii
How to Use this Manual
This manual contains operation and maintenance infor-
mation for the LI-250 Light Meter. Read the operating
instructions before using the LI-250.
NOTICE
The information contained in this document is subject to change
without notice.
LI-COR MAKES NO WARRANTY OF ANY KIND WITH
REGARD TO THIS MATERIAL, INCLUDING, BUT NOT
LIMITED TO THE IMPLIED WARRANTIES OF MER-
CHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE. LI-COR shall not be liable for errors contained herein
or for incidental or consequential damages in connection with the
furnishing, performance, or use of this material.
This document contains proprietary information which is protected
by copyright. All rights are reserved. No part of this document
may be photocopied, reproduced, or translated to another language
without prior written consent of LI-COR, inc.
Copyright 1996, LI-COR, inc.
1st Printing - April, 1996

iii
Table of Contents
Section 1. Operation Summary
1.1 Configuration vs. Measurement Mode..................... 5
1.2 Making Measurements............................................. 5
Section 2. Sensors & Accessories
2.1 Compatible Sensors ................................................. 9
2.2 Sensor Calibration.................................................... 10
2.3 Accessories .............................................................. 13
2.4 Power Requirements ................................................ 13
APPENDIX A. Specifications
APPENDIX B. Conversion Table

5
1Operation Summary
Read this section to configure and operate the LI-250. Note
that programming instructions can also be found on the
LI-250 back panel.
1.1 Configuration vs. Measurement
Mode
The LI-250 has two modes of operation; Configuration and
Measurement mode. In configuration mode, you can enter
calibration multipliers for two different light sensors, or
enter two multipliers for the same sensor. For example,
you might enter a multiplier that applies to measurements
under water and one that applies to measurements in air for
an LI-192SA Underwater Quantum Sensor. In measure-
ment mode the LI-250 makes continuous measurements
until either the HOLD key or the CAL key is pressed.
1.2 Making Measurements
The LI-250 utilizes a 5-key keypad; note that many of the
keys have two functions. The active function depends on
whether the LI-250 is in Measurement or Configuration
mode. In measurement mode, the keys perform the
function shown in green; in configuration mode, the keys
perform the function shown in white.

Operation Summary
6
1. Attach the desired sensor.
2. Press and hold the ON key for about 2 seconds, and
then release to turn the instrument on. You will be in
measurement mode.
3Press CAL to enter configuration mode, where you can
display or change the calibration multiplier currently
in use. The display will show CAL.
4. Press UNITS until the units label on the display
matches the sensor type. Readings will be incorrect if
the Units Label does not match the sensor type.
Sensor Type Units Label Readout Units
Quantum
Pyranometer
Photometric
µmol
W m-2
lux or Klux
µmol s-1 m-2
Watts m-2
lux or Kilolux
5. Press the ↑or ↓keys to change the displayed
multiplier value. Press and hold the arrow keys down
to scroll the values rapidly.
Important Note: Measurement units must
match the sensor type; no unit conversions are
performed.
6. Press CAL again to store the displayed multiplier value
and units label and use them to take measurements; or

Operation Summary
7
7. Press MULT SELECT if you wish to display the second
multiplier. NOTE: Pressing MULT SELECT before
pressing CAL (step 6) discards any changes you have
made to the multiplier currently shown on the display.
8. Edit the second multiplier following steps 5-7 above.
9. Press CAL again to store the displayed multiplier value
and units label and use them to take measurements.
Note that pressing CAL when in measurement mode will
display the multiplier in current use. The multiplier dis-
played when CAL is pressed again will be stored as the
active multiplier, whether you have changed it or not.
While in measurement mode, you can press HOLD to retain
the current reading on the display, until the HOLD key is
pressed again.
Press AVG to perform a 15 second average, which will be
displayed in Hold mode. Press the HOLD key to resume
measurements.
Press the OFF key to turn the power off. The LI-250 will
automatically shut off after 25 minutes of inactivity in
measurement mode.

9
2 Sensors & Accessories
2.1 Compatible Sensors
The LI-250 is compatible with all LI-COR type 'SA' radia-
tion sensors. It is important that the LI-250 be properly
configured for the specific sensor used. A quantum sensor
must be used to make measurements of photosynthetically
active radiation (µmol s-1 m-2 of PAR), a pyranometer for
measurements of solar radiation (W m-2), and a photometric
sensor for measurements of illuminance (lux). For
example, it is not possible for a pyranometer to read out in
units of lux. If you want to configure the LI-250 to read out
in lux, you must use the photometric sensor.
LI-COR type 'SB' radiation sensors are also compatible if
the Calconnector (Calibration connector) is detached from
the BNC connector.
LI-COR type 'SZ' radiation sensors are not compatible with
the LI-250; they may, however, be fitted with a BNC con-
nector. Contact LI-COR for further information.
Recalibration of all LI-COR radiation sensors is rec-
ommended every two years.
Complete information concerning the sensors that can be
used with the LI-250 is found in the type 'SA' LI-COR
Radiation Sensors instruction manuals. In addition, several
technical reports on LI-COR sensors are available. These

Sensors & Accessories
10
include a report entitled "Radiation Measurements", which
summarizes the types of measurements that can be made
with each LI-COR sensor and contains conversion factors
for commonly used measurement units. A report concern-
ing the immersion effect and cosine collecting properties of
underwater sensors is also available (Roemer, Hoagland
report. Request Application Note #110).
2.2 Sensor Calibration
All LI-COR radiation sensors produce a current pro-
portional to the radiation intensity. During factory cali-
bration, sensor output (in microamps) is measured while the
sensor is exposed to a standard lamp of known intensity.
The sensor output at this intensity has general units of
microamps per radiation unit and is called the Calibration
Constant (Calconstant). Each sensor has a slightly differ-
ent output at a given radiation intensity and will therefore
have a unique Calconstant.
The LI-250 measures the current output of the sensor in
units of microamps, and converts the measured current to
units of radiation. To make this conversion, the LI-250
uses the sensor Calibration Multiplier. The Calibration
Multiplier is the negative reciprocal of the Calconstant.
Multiplier Calcons t =−1tan
The Calibration Multiplier is always a negative number (be-
cause the shield of the coaxial cable is positive instead of
negative), and is expressed in radiation units per microamp.

Sensors & Accessories
11
The LI-250 multiplies the current reading in microamps by
the multiplier.
Since the Calibration Multiplier is unique for each sensor, it
must be entered into the LI-250 each time the sensor is
changed or recalibrated.
NOTE: Always enter the Calibration Multiplier, not
the Calconstant. If the Calconstant is entered any data
collected will be erroneous.
For type 'SA' sensors purchased after September, 1985, the
calibration multiplier is given on the certificate of calibra-
tion, and is also attached to the sensor. An example of a
calibration label attached to a quantum sensor appears
below, which would contain the value of the multiplier, as
well as the serial number of the sensor, and the date of its
most recent calibration.
NOTE: Tcoff is a time coefficient that is used to convert
integrated data to the proper units when using the LI-1000
Datalogger to log data with certain sensors. This value can
be ignored when using the LI-250.
MULT: XXX.XX
tcoff: 0.0036
Units: µmol s-1 m-2 per µA
SERIAL NO.
CAL DATE: DD/MM/YR
®