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
®

Sensors & Accessories
12
For the LI-192SA and LI-193SA Underwater Quantum
Sensors there are two calibration multipliers; one for "in
air" operation and one for "in water" operation. Use the
multiplier that is appropriate for your application.
If the calibration constant for your sensor has been lost or
misplaced, it can be obtained from LI-COR by providing
the serial number of the sensor.
Converting Calconstants to Multipliers
For LI-COR sensors that are not type 'SA' (i.e., type 'SB',
etc.), the calibration multiplier must be calculated from the
calibration constant given on the certificate of calibration.
EXAMPLE: Calculate the multiplier for an LI-190SB
Quantum sensor with a calibration constant of 8.0
µAmps/1000 µmol s-1 m-2.
Multiplier =−
( )
µ
( )
µ
1 1000
8
s m
Amps
-1 -2
mol
=−µ
µ
125 0
1
. mol s m
Amp
-1 -2

Sensors & Accessories
13
2.3 Accessories
The following accessories and sensors are available for the
LI-250. Contact LI-COR for current information.
250-01 Carrying Case - A soft-sided case for the LI-250
and terrestrial type radiation sensors. Size: 20.3 cm L ×
10.2 cm W × 9 cm D (8" ×4" ×3.5"). Weight: 98 g (0.216
lbs).
LI-COR Radiation Sensors: Type 'SA' (e.g. LI-190SA)
with BNC connectors.
LI-190SA Quantum Sensor - measures Photosynthetically
Active Radiation (PAR) in natural sunlight, under plant
canopies, and in growth chambers and greenhouses.
LI-191SA Line Quantum Sensor - averages PPFD over its
one meter length for plant canopy PPFD profile studies.
LI-192SA Underwater Quantum Sensor* - measures
Photosynthetic Photon Flux Density (PPFD) in air or under
water incident on a flat plane.
LI-193SA Spherical Quantum Sensor* - measures photon
flux from all directions under water. This measurement is
called Photosynthetic Photon Flux Fluence Rate (PPFFR).
LI-200SA Pyranometer Sensor - measures global solar
radiation (sun plus sky) and provides a typical accuracy of
±5% under unobstructed daylight conditions.
LI-210SA Photometric Sensor - measures visible radiation
and has a spectral response equal to that for the average
human eye. Readout of illuminance (in lux) is used for
lighting studies or architectural modeling.
* Requires 2222UWB cable.

Sensors & Accessories
14
2003S Mounting and Leveling Fixture - The 2003S is for
use with all LI-COR terrestrial type sensors.
2222SB Extension Cable - For use with all LI-COR ter-
restrial type sensors. Available in 15.2 m (50 ft), 30.4 m
(100 ft), or custom lengths to 304 m (1000 ft).
216 Replacement Battery - 9 Volt transistor type. The
LI-250 requires one for replacement.
2.4 Power Requirements
Power is supplied by one 9 volt transistor battery.
Eveready alkaline #522 (LI-COR part #216) or equivalent
may be used. Battery life is in excess of 150 hours. A LO
BAT message is displayed when there is less than 20 hours
of battery life remaining. The battery should be replaced
immediately after the LO BAT message is displayed to en-
sure reliable operation.
The battery compartment is accessed through a slide-out
panel on the back of the instrument case.
Although typical battery life is more than 150 hours of
continuous operation, it is dependent upon the storage tem-
perature. Do not store the LI-250 at high temperatures.

A-1
Appendix A. Specifications
Accuracy: 25 °C: Typically ±0.4% of reading [(±3
counts on the least significant digit displayed (all ranges)].
0-55 °C: Typically ± 0.6% of reading [(± 3 counts on the
least significant digit displayed (all ranges)].
Range Selection: Autoranging (3 ranges).
Sensor Calibration: Calibration multipliers for two
sensors are stored in memory. Calibration multipliers are
entered from the keypad.
Sensor Averaging: Sensor output is averaged for 15
seconds when AVG key is pressed in Measurement mode.
Averages are displayed in HOLD mode to retain the
average on the display.
Linearity: ±0.05%.
Operating Conditions: 0 to 55 °C, 0 to 95% RH (non-
condensing).
Storage Conditions: -55 to 60 °C, 0 to 95% RH
(non-condensing).
Display: 4 1/2 digit custom LCD display. Updated every
0.5 seconds.
Keypad: Sealed, 5-key tactile response keypad.
Battery Life: 150 hours typical with continuous operation.
Automatic shutoff after 25 minutes of inactivity in
measurement mode.
Power Requirement: One 9V Eveready Alkaline #522 or
equivalent.

Specifications
A-2
Low Battery Detection: Low battery indicator displayed
with approximately 20 hours battery life remaining.
Size: 14 L ×7.7 W ×3.8 cm D (5.5" ×3" ×1.5").
Weight: 0.26 kg (0.57 lbs).
Sensors: Any LI-COR sensor with BNC connector;
Quantum, Pyranometer, or Photometric.
Warranty: 1 year parts and labor.
LI-250 Range and Resolution:
Sensor Type
Quantum
Radiometric
Photometric
Range Resolution
0-199 µmol s-1 m-2
-1999
-19999
0-19 W m-2
-199
-1999
0-1999 lux
-19999 lux
0-199 klux
0-199 fc
-1999
-19999
0.01 µmol s-1 m-2
0.1
1
0.001 W m-2
0.01
0.1
0.1 lux
1 lux
0.01 klux
0.01 fc
0.1
1

B-1
Appendix B. Conversion Table
Type of
Measurement Instantaneous Measurements
Quantum 1.0 µm s-1 m-2 = 1 µEs-1 m-2
= 6.022 • 1017 photons s-1m-2
= 6.022 •1017 quanta s-1 m-2
= 6.022 •1013 quanta s-1 cm-2
Radiometric 1 W m-2 = 1.433 •10-3 cal cm-2 min-1
= 1.433 •10-3 langley min-1
= 0.100 mW cm-2
= 100 µW cm-2
= 1.0 J s-1 m-2
= 1000 erg s-1 cm-2
= 0.317 BTU ft-2 h-1
= 5.283 •10-3 BTU ft-2 min-1
Photometric 1 lux = 1 lm m-2
= 0.0929 lm ft-2
= 0.0929 fc
= 0.001 klux

Warranty
Each LI-COR, inc. instrument is warranted by LI-COR, inc. to be
free from defects in material and workmanship; however,
LI-COR, inc.'s sole obligation under this warranty shall be to repair
or replace any part of the instrument which LI-COR, inc.'s
examination discloses to have been defective in material or
workmanship without charge and only under the following
conditions, which are:
1. The defects are called to the attention of LI-COR, inc. in
Lincoln, Nebraska, in writing within one year after the shipping
date of the instrument.
2. The instrument has not been maintained, repaired, or altered by
anyone who was not approved by LI-COR, inc.
3. The instrument was used in the normal, proper, and ordinary
manner and has not been abused, altered, misused, neglected,
involved in and accident or damaged by act of God or other
casualty.
4. The purchaser, whether it is a DISTRIBUTOR or direct
customer of LI-COR or a DISTRIBUTOR'S customer, packs and
ships or delivers the instrument to LI-COR, inc. at LI-COR inc.'s
factory in Lincoln, Nebraska, U.S.A. within 30 days after
LI-COR, inc. has received written notice of the defect. Unless
other arrangements have been made in writing, transportation to
LI-COR, inc. (by air unless otherwise authorized by LI-COR, inc.)
is at customer expense.
5. No-charge repair parts may be sent at LI-COR, inc.'s sole
discretion to the purchaser for installation by purchaser.
6. LI-COR, inc.'s liability is limited to repair or replace any part of
the instrument without charge if LI-COR, inc.'s examination

disclosed that part to have been defective in material or
workmanship.
There are no warranties, express or implied, including but not
limited to any implied warranty of merchantability of fitness
for a particular purpose on underwater cables or on
expendables such as batteries, lamps, thermocouples and
calibrations.
Other than the obligation of LI-COR, inc. expressly set forth
herein, LI-COR, inc. disclaims all warranties of
merchantability or fitness for a particular purpose. The
foregoing constitutes LI-COR, inc.'s sole obligation and
liability with respect to damages resulting from the use or
performance of the instrument and in no event shall LI-COR,
inc. or its representatives be liable for damages beyond the
price paid for the instrument, or for direct, incidental or
consequential damages.
The laws of some locations may not allow the exclusion or
limitation on implied warranties or on incidental or consequential
damages, so the limitations herein may not apply directly. This
warranty gives you specific legal rights, and you may already have
other rights which vary from state to state. All warranties that
apply, whether included by this contract or by law, are limited to
the time period of this warranty which is a twelve-month period
commencing from the date the instrument is shipped to a user who
is a customer or eighteen months from the date of shipment to
LI-COR, inc.'s authorized distributor, whichever is earlier.
This warranty supersedes all warranties for products purchased
prior to June 1, 1984, unless this warranty is later superseded.

DISTRIBUTOR or the DISTRIBUTOR'S customers may ship the
instruments directly to LI-COR if they are unable to repair the
instrument themselves even though the DISTRIBUTOR has been
approved for making such repairs and has agreed with the
customer to make such repairs as covered by this limited warranty.
Further information concerning this warranty may be obtained by
writing or telephoning Warranty manager at LI-COR, inc.
IMPORTANT: Please return the User Registration Card enclosed
with your shipment so that we have an accurate record of your
address. Thank you.