Kipp & Zonen PAR lite User manual

Instruction Manual
Photosynthetic Active Radiometer
PAR lite

IMPORTANT USER INFORMATION
Reading this entire manual is recommended for full
understanding of the use of this product
The exclamation mark within an equilateral triangle is intended to alert the
user to the presence of important operating and maintenance instructions
in the literature accompanying the instrument.
Should you have any comments on the product or this manual we will be
pleased to receive them at:
Kipp & Zonen B.V.
Delftechpark 36
2628 XH Delft Holland
P.O. Box 507 2600 AM Delft Holland
Phone [phone]
Fax [phone]
Email [email protected]
Web www.kippzonen.com
Kipp & Zonen reserve the right to make changes in the specifications
without prior notice.

IMPORTANT USER INFORMATION
WARRANTY AND LIABILITY
the Kipp & Zonen guarantees that the product delivered has been
thoroughly tested to ensure that it meets its published specifications. The
warranty included in conditions of delivery is valid only if the product has
been installed and used according to the instructions supplied by Kipp &
Zonen.
User made modifications can affect the validity of the CE declaration.
Kipp & Zonen shall in no event be liable for incidental or consequential
damages, including without limitation, lost profits, loss of income, loss of
business opportunities, loss of use and other related exposures, however
caused, arising from the faulty and incorrect use of the product.
COPYRIGHT©2004 KIPP & ZONEN
All rights reserved. No part of this publication may be reproduced, stored in
a retrieval system or transmitted in any form or by any means, without
permission in written form from the company.
Manual version 0706

CONTENTS
Instruction manual PAR-LITE 1
Contents
1 General information....................................................... 3
1.1 Five minutes user guide................................................ 4
2 Sensor properties.......................................................... 7
2.1 Electrical........................................................................7
2.2 Spectral.........................................................................9
2.3 Directional / Cosine response.....................................10
2.4 List of specifications.................................................... 12
2.5 Dimensions.................................................................. 14
2.6 Expected output levels................................................ 15
3 Calibration .................................................................... 17
4 Installation and maintenance ..................................... 19
4.1 Recalibration ...............................................................20
4.2 Adjustment of calibration factor................................... 20

CONTENTS
Instruction manual PAR-LITE 2
4.3 Measuring modulated light..........................................21
5 Trouble shooting.......................................................... 23
6 Delivery......................................................................... 25
7 Accessories.................................................................. 27

CONTENTS
Instruction manual PAR-LITE 3

GENERAL INFORMATION
Instruction manual PAR-LITE 4
1 General information
The PAR LITE is an instrument for the measurement of
Photosynthetic Photon Flux Density. In practise this quantity is
called PAR, which stands for Photosynthetically Active
Radiation. This measurement represents the number of
photons between 400 and 700 nm incident per square meter
per second. These photons can be used by green plants for
the process of photosynthesis. PAR LITE measures the
photons that are received from the entire hemisphere (180
degrees field of view). The output is expressed in micro mol
per second per square meter.
The PAR LITE is designed for continuous outdoor use. Its
calibration is valid for natural sunlight , for artificial light it will
be less accurate. See the section on spectral sensor
properties and calibration.
In its most frequent application the PAR sensor is used for
agrometeorological and horti-culture applications. Typically it
will be installed in a meteo-mast and face upwards. It can
however be used to measure in an inverted or in a tilted
position.
Contrary to similar designs of other brands, the PAR LITE is
not equipped with a level. The reason is that for the kind of
accuracy that this sensor can offer, leveling does not need to
be accurate. The levelling with a level instrument over the
rim/diffuser during installation suffices. A check on the levelling

GENERAL INFORMATION
Instruction manual PAR-LITE 5
can be done in the same way. A levelling fixture is available as
an option.
The PAR-LITE fully complies CE with directive 89/336/EEC

GENERAL INFORMATION
Instruction manual PAR-LITE 6
1.1 Five minutes user guide
Requirements:
1. PAR LITE
2. voltmeter with a range from 0 to 20 millivolt and an
3. input impedance of more than 50 kΩ
3. light
•Connect the white wire to the voltmeter+, the green wire
to the voltmeter-, the shield to the ground.
•Position the instrument as such that the sensor is parallel
to the surface that you want to investigate.
•Put the voltmeter to the most sensitive range.
•Darken the sensor. The signal should read zero.
•Expose the sensor to light. The signal should give a
positive reading.
•Adjust the voltmeter range in such a way that the
expected full scale output of the PAR LITE fits the full
scale input of the voltmeter. This can be done on
theoretical considerations. (When the maximum expected
radiation outdoors is 2 000 micro mol per second per
square metre, and the sensitivity of the PAR LITE is 5
microvolts per micro mol per second per square metre,
the expected output range of the PAR LITE is 2000 times
5 makes 10000 microvolts or 10 millivolts.) Please note
that the calibration is valid for natural sunlight only.

GENERAL INFORMATION
Instruction manual PAR-LITE 7
•Calculate the radiation intensity by dividing the PAR LITE
output (10 millivolts) by the calibration factor
( 5 µV/µmol/s.m2).
•For permanent installation mounting should be done
using the holes through the PAR LITE body, or through
the holes in the optional levelling fixture. The sensor
should be mounted in a field which is free from
obstructions. Unless this is unavoidable, no shadow
should be cast upon it.
•Maintenance: the sensor should be kept clean, using
water or alcohol.
•Recalibration is suggested every two years, preferably by
letting a higher standard run parallel to it during two
different days, a clear day and a cloudy day and by
comparing the daily totals.

SENSOR PROPERTIES
Instruction manual PAR-LITE 8
2 Sensor properties
The PAR LITE consists of a photodiode, filters, a diffuser, a
housing and a cable.
The photodiode is shunted by a resistance. This is done to
generate a voltage output. Most electrical specifications are
determined by the photodiode and the resistor. Spectral
specifications are determined by the photodiode, the filters
and the diffusor material. The diffusor ensures a field of view
of 180 degrees, and angular characteristics fulfilling the so-
called cosine response.
2.1 Electrical
The electrical circuit of the PAR LITE is drawn in figure 1. The
nominal output resistance of the PAR LITE is 240 Ω. This
implies that the input impedance of the readout equipment
should be at least 30 kΩin order to make an error of less than
1 percent.
Cable can be extended without problems to a length of 100
metres, provided that cable resistance is less than 0.1 percent
of the input impedance of the readout equipment.
The electrical sensitivity of the photodiode changes with the
temperature. A typical value for this is -0.1 percent change per
degree Celsius.
Calibration is done at approx. 25° Celsius.

SENSOR PROPERTIES
Instruction manual PAR-LITE 9
Figure 1 Electrical circuit of the PAR LITE, white +.

SENSOR PROPERTIES
Instruction manual PAR-LITE 10
2.2 Spectral
The spectral properties of the PAR LITE are mainly
determined by the properties of the photodiode and the filter.
The spectral sensitivity is indicated in figure 2.
Figure 2. The relative spectral sensitivity of the PAR LITE sensor
and the ideal PAR spectral response together with the
spectrum of the sun under a clear sky (airmass 1.5) and
the relative spectrum of a lamp with a colortemperature
of 2856 K.
The sensor follows more or less the characteristic of a so-
called quantum response between 400 and 700 nm. This is
said to be the spectral area which is utilised by plants for
photosynthesis. For the photosynthesis each photon has an
equal significance. Because photons of a lower wavelength

SENSOR PROPERTIES
Instruction manual PAR-LITE 11
have higher energy content, the spectral sensitivity of a PAR
sensor has to be low for low wavelengths and higher for higher
wavelengths. This explains the inclination of the spectral
sensitivity curve.
The PAR LITE has been calibrated for solar radiation under
clear sky conditions. The spectrum under these circumstances
is also drawn in figure 2.
Some plants however are grown under lamps. The spectral
emission of this lamps is mainly in the wavelength range from
500 – 600 nm. This implies that actually the mean spectral
sensitivity of the PAR LITE in the range of 500 – 600 nm
should be used. This sensitivity can differ from the sensitivity
for daylight, which is also determined by the individual
bandwidth of the PAR LITE sensor. Deviations can be of the
order of magnitude of ±5 %. Read also chapter 3, Calibration,
for this matter.
2.3 Directional/Cosine response
The measurement of radiation received by a surface (also
called irradiance or radiative flux) is laid down in two detector
specifications: that the detector has a correct spectral
response and that it has a field of view of 180 degrees.
Another way of expressing the latter directional properties is to
say that the sensor has to comply with the cosine response.
A perfect cosine response will show maximum sensitivity at an
angle of incidence of 0°(perpendicular to the sensor surface)
and zero sensitivity at an angle of incidence of 90°(radiation
passing over the sensor surface). In between 0° and 90° the

SENSOR PROPERTIES
Instruction manual PAR-LITE 12
sensitivity should be proportional to the cosine of the angle of
incidence. Figure 3 shows the behaviour of a typical PAR
LITE. The vertical axis shows the deviation from ideal
behaviour, expressed in percentage of the ideal value.
Figure 3. The directional response or cosine response of the PAR
LITE. On the horizontal axis the zenith angle
On the vertical axis the percentage deviation from ideal
cosine behaviour.
The curve can lift or fall for different azimuth (+ or – 2.5%
at 70º zenith angle).
-6
-4
-2
0
2
4
6
0 20406080
ZENITH ANGLE (degrees)

SENSOR PROPERTIES
Instruction manual PAR-LITE 13
2.4 List of specifications
Electrical
•Impedance (nominal): 240 Ω
•Response time: < 0.1 s
•Sensitivity: 4 - 6 µV/µmol/s.m2
•Expected signal range under
atmospheric conditions: 0 – 12 mV
•Non-stability: within ± 2%/year
•Non linearity: within ± 1%
up to 10000 µmol /s.m2
•Temperature
dependence of sensitivity: within ± 0.2%/°C
(-0.1% typ.)
Spectral
Detector type: Silicon photodiode plus
filters
•Spectral range (nominal): 400 - 700 nm
•Cut on (50 %) 400 ± 15 nm
•Cut off (50 %) 700 ± 15 nm
•Quantumresponse match error
(450 – 650 nm) within ± 10 %

SENSOR PROPERTIES
Instruction manual PAR-LITE 14
Directional
•Cosine corrected between 0 and 800
Error up to 80°angle of incidence, within ± 10 %
•azimuth error (at 70°angle of incidence): < 5 %pp
•Tilt response: no error
Mechanical
•Material of housing: Anodized
Aluminium
•Material of cable: Poly Urethane
•Weight: 110 g
•Cable length: 3 metres
•Dimensions see figure 4
Environmental
•Operating temperature range: -30 - +70 °C
•Humidity 0 - 100 % RH

SENSOR PROPERTIES
Instruction manual PAR-LITE 15
2.5 Dimensions
Figure 4. The dimensions of the PAR LITE in mm, white lead
positive, green lead negative.

SENSOR PROPERTIES
Instruction manual PAR-LITE 16
2.6 expected output levels
Cloud
condition
Pyranometer
reading W/m2
PAR sensor
reading
µmol/s.m2
µmol/W.s
+/- 10%
Cloudless Typ 0 to 1300 Typ 0 to 2600 2,0
Cloudy Typ 0 to 500 Typ 0 to 1250 2.5
Table 1: Conversion from W/m2to µmol/s.m2under cloudless
and cloudy conditions. The table serves as a rough
cross-check when also measuerments of the solar
irradiance in W/m2are available.

SENSOR PROPERTIES
Instruction manual PAR-LITE 17
Cloud
condition
Pyranometer
daily total
W.h/m2
PAR sensor
daily total
mol/m2
Cloudless Up to 11000 Up to 80
Cloudy Up to 4500 Up to 40
Table 2: expected daily totals; the figures are indicative