Symbols and Terminology
Vishay Semiconductors
Symbols and Terminology
A
anode
Anode terminal
A
ampere
SI unit of electrical current
A
radiant sensitive area
That area which is radiant sensitive for a specified range
a
distance
E.g. a distance between the emitter (source)
and the detector
B
base
Base terminal
BER Bit Error Rate
bit/s data rate or signaling rate
1000 bit/s = 1 kbit/s, 106 bit/s = 1 Mbit/s
C
capacitance
Unit: F (farad) = C/V
C
coulomb
C=As
C
cathode, cathode terminal
C
collector, collector terminal
°C
degree Celsius
Celsius temperature, symbol t, and is defined
by the quantity equation t = T - T0.
The unit of Celsius temperature is the degree
Celsius, symbol °C. The numerical value of a
Celsius temperature t expressed in degrees
Celsius is given by t / °C = T / K – 273.15
It follows from the definition of t that the degree
Celsius is equal in magnitude to the kelvin,
which in turn implies that the numerical value of
a given temperature difference or temperature
interval whose value is expressed in the unit
degree Celsius (°C) is equal to the numerical
value of the same difference or interval when
its value is expressed in the unit kelvin (K)
cd
candela
SI unit of luminous intensity. The candela is the
luminous intensity, in a given direction, of a
source that emits monochromatic radiation of
frequency 540 x 1012 hertz and that has a radiant intensity in that direction of
1/683 watt per steradian. (16th General Conference of Weights and Measures, 1979)
1 cd = 1 lm sr-1
CD
diode capacitance
Total capacitance effective between the diode
terminals due to case, junction and parasitic
capacitances
Document Number: 82512
Rev. 1.4, 06-Oct-06
Cj
junction capacitance
Capacitance due to a pn junction of a diode,
decreases with increasing reverse voltage
d
apparent (or virtual) source size
(of an emitter)
The measured diameter of an optical source
used to calculate the eye safety laser class of
the source. See IEC60825-1 and
EN ISO 11146-1
E
emitter
Emitter terminal (phototransistor)
EA
illumination at standard illuminant A
According to DIN 5033 and IEC 306-1, illumination emitted from a tungsten filament lamp
with a color temperature Tf = 2855.6 K, which
is equivalent to standard illuminant A
Unit: lx (Lux) or klx
EA amb ambient illumination at standard illuminant A
echo - off
Unprecise term to describe the behavior of the
output of IrDA® transceivers during transmission. "echo – off" means that by blocking the
receiver the output Rxd is quiet during transmission
echo - on
Unprecise term to describe the behavior of the
output of IrDA® transceivers during transmission. "echo – on" means that the receiver output Rxd is active but often undefined during
transmission. For correct data reception after
transmission the receiver channel must be
cleared during the latency period
Ee, E irradiance (at a point of a surface)
Quotient of the radiant flux d)e incident on an
element of the surface containing the point, by
the area dA of that element. Equivalent definition. Integral, taken over the hemisphere visible
from the given point, of the expression
Le cosT d:, where Le is the radiance at the
given point in the various directions of the incident elementary beams of solid angle d:, and
T is the angle between any of these beams and
the normal to the surface at the given point
Ee
d)
= --------e- =
dA
³
L e cos T d : 2 S sr
Unit: W m-2
Ev, E illuminance (at a point of a surface)
Quotient of the luminous flux d)v incident on
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31
Symbols and Terminology
Vishay Semiconductors
an element of the surface containing the point,
by the area dA of that element.
Equivalent defnition. Integral, taken over the
hemisphere visible from the given point, of the
expression Lv cosT d:, where Lv is the luminance at the given point in the various directions of the incident elementary beams of solid
angle d:, and T is the angle between any of
these beams and the normal to the surface at
the given point
d )v
E v = --------- =
L v cos T d : dA
Ie, I
³
2 S sr
Unit: lx = lm m-2
F
farad
Unit: F = C/V
f
frequency
Unit: s-1, Hz (Hertz)
fc, fcd cut-off frequency – detector devices
The frequency at which, for constant signal
modulation depth of the input radiant power,
the demodulated signal power has decreased
to ½ of its low frequency value. Example: The
incident radiation generates a photocurrent or
a photo voltage 0.707 times the value of radiation at f = 1 kHz
(3 dB signal drop, other references may occur
as e.g. 6 dB or 10 dB)
fs
switching frequency
FIR Fast Infrared, as SIR, data rate 4 Mbit/s
Ia
light current
General: Current which flows through a device
due to irradiation/illumination
IB
base current
IBM base peak current
IC
collector current
Ica
collector light current
Collector current under irradiation
Collector current which flows at a specified illumination/irradiation
ICEO collector dark current, with open base
Collector-emitter dark current
For radiant sensitive devices with open base
and without illumination/radiation
(E = 0)
ICM repetitive peak collector current
idle Mode of operation where the device (e.g. a
transceiver) is fully operational and expecting
to receive a signal for operation e.g in case of
a transceiver waiting to receive an optical input
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32
IF
IFAV
IFM
IFSM
Ik
Io
Iph
IR
IR
Ira
IrDA®
IRED
Iro
or to send an optical output as response to an
applied electrical signal
radiant intensity (of a source, in a given
direction)
Quotient of the radiant flux d)e leaving the
source and propagated in the element of solid
angle d: containing the given direction, by the
element of solid angle
Ie = d)e/d:
Unit: W sr-1
Note: The radiant intensity Ie of emitters is typically measured with an angle < 0.01 sr on
mechanical axis or off-axis in the maximum of
the irradiation pattern
continuous forward current
The current flowing through a diode in the forward direction
average (mean) forward current
peak forward current
surge forward current
short-circuit current
That value of the current which flows when a
photovoltaic cell or a photodiode is short circuited (RL << Ri ) at its terminals
dc output current
photocurrent
That part of the output current of a photoelectric detector, which is caused by incident radiation
reverse current, leakage current
Current which flows through a reverse biased
semiconductor pn-junction
Abbreviation for infrared
reverse current under irradiation
Reverse light current which flows due to a
specified irradiation/illumination in a photoelectric device
Ira = Iro + Iph
Infrared Data Association
No profit organization generating infrared data
communication standards
infrared emitting diode
Solid state device embodying a p-n junction,
emitting infrared radiation when excited by an
electric current. See also LED:
Solid state device embodying a p-n junction,
emitting optical radiation when excited by an
electric current.
reverse dark current, dark current
Reverse current flowing through a photoelectric device in the absence of irradiation
Document Number: 82512
Rev. 1.4, 06-Oct-06
Symbols and Terminology
Vishay Semiconductors
IrPHY version 1.0
SIR IrDA®‚ data communication specification
covering data rates from 2.4 kbit/s to
115.2 kbit/s and a guaranteed operating range
more than one meter in a cone of ± 15°
IrPHY version 1.1
MIR and FIR were implemented in the IrDA®
standard with the version 1.1, replacing version
1.0
IrPHY version 1.2
Added the SIR Low Power Standard to the
IrDA® standard, replacing version 1.1.
The SIR Low Power Standard describes a current saving implementation with reduced range
(min. 20 cm to other Low Power Devices and
min. 30 cm to full range devices).
IrPHY version 1.3
extended the Low Power Option to the higher
bit rates of MIR and FIR replacing version 1.2.
IrPHY version 1.4
VFIR was added, replacing version 1.3
ISB quiescent current
ISD supply current in dark ambient
ISH supply current in bright ambient
Iv, I luminous intensity (of a source, in a given
direction)
Quotient of the luminous flux d)v leaving the
source and propagated in the element of solid
angle d: containing the given direction, by the
element of solid angle
Ie = d)v/d:
Unit: cd sr-1
Note: The luminous intensity Iv of emitters is
typically measured with an angle < 0.01 sr on
mechanical axis or off-axis in the maximum of
the irradiation pattern
K
luminous efficacy of radiation
Quotient of the luminous flux )v by the corresponding radiant flux )e:
K = )v / ) e
Unit: lm W-1
Note: When applied to monochromatic radiations, the maximum value of K(O) is denoted by
the symbol Km
Km = 683 lm W-1 for Qm = 540 1012 Hz
(Om | 555 nm) for photopic vision.
K'm = 1700 lm W-1 for O'm | 507 nm for
scotopic vision. For other wavelengths:
K(O) = Km V(O) and K'(O) = K'm V'(O)
K
kelvin
SI unit of thermodynamic temperature, is the
fraction 1/273.15 of the thermodynamic temDocument Number: 82512
Rev. 1.4, 06-Oct-06
perature of the triple point of water (13th CGPM
(1967), Resolution 4). The unit kelvin and its
symbol K should be used to express an interval
or a difference of temperature.
Note: In addition to the thermodynamic temperature (symbol T), expressed in kelvins, use is
also made of Celsius temperature (symbol t )
defined by the equation t = T-T0, where
T0 = 273.15 K by definition. To express Celsius
temperature, the unit "degree Celsius", which
is equal to the unit "kelvin" is used; in this case,
"degree Celsius" is a special name used in
place of "kelvin". An interval or difference of
Celsius temperature can, however, be
expressed in kelvins as well as in degrees Celsius
Latency
receiver latency allowance (in ms or μs) is
the maximum time after a node ceases transmitting before the node’s receiving recovers its
specified sensitivity
LED and IRED
Light Emitting Diode
LED: Solid state device embodying a p-n junction, emitting optical radiation when excited by
an electric current. The term LED is correct
only for visible radiation, because light is
defined as visible radiation (see “Radiation and
Light”). For infrared emitting diodes the term
IRED is the correct term. Nevertheless it is
common but not correct to use "LED" also for
IREDs
Le; L radiance (in a given direction, at a given point
of a real or imaginary surface)
Quantity defined by the formula
Le
lm
lx
m
d)
v
= -------------------------------- ,
dA cos T d :
where d)e is the radiant flux transmitted by an
elementary beam passing through the given
point and propagating in the solid angle d:
containing the given direction; dA is the area of
a section of that beam containing the given
point; T is the angle between the normal to that
section and the direction of the beam
Unit: W m-2 sr-1
lumen
Unit for luminous flux
lux
Unit for illuminance
meter
SI unit of length
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33
Symbols and Terminology
Vishay Semiconductors
Me; M radiant exitance (at a point of a surface)
Quotient of the radiant flux d)e leaving an element of the surface containing the point, by the
area dA of that element. Equivalent definition.
Integral, taken over the hemisphere visible
from the given point, of the expression
Le cosT d:, where Le is the radiance at the
given point in the various directions of the emitted elementary beams of solid angle d:, and T
is the angle between any of these beams and
the normal to the surface at the given point.
d)
M e = ----------e- =
dA
³
2Ssr
L e cos T d :
Unit: W m-2
MIR Medium speed IR, as SIR, with the data rate
576 kbit/s to 1152 kbit/s
Mode Electrical input or output port of a transceiver
device to set the receiver bandwidth
N.A. Numerical Aperture
N.A. = sin D/2
Term used for the characteristic of sensitivity or
intensity angles of fiber optics and objectives
NEP Noise Equivalent Power
Ptot total power dissipation
Pv
power dissipation, general
Radiation and Light
visible radiation
Any optical radiation capable of causing a
visual sensation directly.
Note: There are no precise limits for the spectral range of visible radiation since they depend
upon the amount of radiant power reaching the
retina and the responsivity of the observer. The
lower limit is generally taken between 360 nm
and 400 nm and the upper limit between
760 nm and 830 nm
Radiation and Light
optical radiation
Electromagnetic radiation at wavelengths
between the region of transition to X-rays
( O = 1 nm) and the region of transition to radio
waves ( O = 1 mm)
Radiation and Light IR
infrared radiation
Optical radiation for which the wavelengths are
longer than those for visible radiation. Note:
For infrared radiation, the range between
780 nm and 1 mm is commonly sub-divided
into: IR-A 780 nm to 1400 nm
IR-B 1.4 μm to 3 μm
IR-C 3 μm to 1 mm
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34
RD
RF
Ri
Ris
RL
RS
Rsh
dark resistance
feedback resistor
internal resistance
isolation resistance
load resistance
serial resistance
shunt resistance
The shunt resistance of a detector diode is the
dynamic resistance of the diode at zero bias.
Typically it is measured at a voltage of 10 mV
forward or reverse, or peak-to-peak
RthJA thermal resistance, junction to ambient
RthJC thermal resistance, junction to case
RXD electrical data output port of a transceiver
device
s
second
SI unit of time 1 h = 60 min = 3600 s
S
absolute sensitivity
Ratio of the output value Y of a radiant-sensitive device to the input value X of a physical
quantity: S = Y/X
Units: E.g. A/lx, A/W, A/(W/m2)
s(Op) spectral sensitivity at a wavelength Op
s(O) absolute spectral sensitivity at a wavelength O
The ratio of the output quantity y to the radiant
input quantity x in the range of wavelengths
O to O +'O:
s(O) = dy(O)/dx(O).
E.g., the radiant power )e(O) at a specified
wavelength O falls on the radiationsensitive
area of a detector and generates a photocurrent Iph. s(O) is the ratio between the generated
photocurrent Iph and the radiant power )e(O)
which falls on the detector:
s(O) = Iph / )e(O)
Unit: A/W
s(O)rel spectral sensitivity, relative
Ratio of the spectral sensitivity s(O) at any considered wavelength to the spectral sensitivity
s(O0) at a certain wavelength O0 taken as a reference:
s(O)rel = s(O)/s(O0)
s(O0) spectral sensitivity at a reference wavelength O0
SC Electrical input port of a transceiver device to
set the receiver sensitivity
SD Electrical input port of a transceiver device to
shut down the transceiver
shutdown
Mode of operation where a device is switched
to a sleep mode (shut down) by an external signal or after a quiescent period keeping some
Document Number: 82512
Rev. 1.4, 06-Oct-06
Symbols and Terminology
Vishay Semiconductors
functions alive to be prepared for a fast transition to operating mode. Might be in some cases
identical with "Standby"
SIR Serial Infrared,
Term used by IrDA® to describe infrared data
transmission up to and including 115.2 kbit/s.
SIR IrDA® data communication covers 2.4 kbit/s
to 115.2 kbit/s, equivalent to the basic serial
infrared standard introduced with the physical
layer version IrPhy version 1.0
split power supply
Term for using separated power supplies for
different functions in transceivers. Receiver circuits need well-controlled supply voltages.
IRED drivers don’t need a controlled supply
voltage but need much higher currents. Therefore it safes cost not to control the IRED current
supply and have a separated supply. For that
some modified design rules have to be taken
into account for designing the ASIC. This is
used in nearly all Vishay transceivers and is
described in US-Patent No. 6,157,476
sr
steradian (sr)
SI unit of solid angle :
Solid angle that, having its vertex at the centre
of a sphere, cuts off an area of the surface of
the sphere equal to that of a square with sides
of length equal to the radius of the sphere.
(ISO, 31/1-2.1, 1978)
Example:
The unity solid angle, in terms of geometry, is
the angle subtended at the center of a sphere
by an area on its surface numerically equal to
the square of the radius (see figures below)
Other than the figures might suggest, the
shape of the area doesn't matter at all. Any
shape on the surface of the sphere that holds
the same area will define a solid angle of the
same size. The unit of the solid angle is the
steradian (sr). Mathematically, the solid angle
is dimensionless, but for practical reasons, the
steradian is assigned
Standby
Mode of operation where a device is prepared
to be quickly switched into an idle or operating
mode by an external signal
T
period of time (duration)
T
temperature
0 K = – 273.15 °C
Unit: K (kelvin)
t
temperature
°C (degree Celsius)
Document Number: 82512
Rev. 1.4, 06-Oct-06
Instead of t sometimes T is used not to mix up
temperature T with time t
t
time
Tamb ambient temperature
If self-heating is significant: temperature of the
surrounding air below the device, under conditions of thermal equilibrium. If self-heating is
insignificant: air temperature in the surroundings of the device
Tamb ambient temperature range
As an absolute maximum rating: The maximum
permissible ambient temperature range
TC
temperature coefficient
The ratio of the relative change of an electrical
quantity to the change in temperature ('T)
which causes it under otherwise constant operating conditions
TC
colour temperature (BE)
The temperature of a Planckian radiator whose
radiation has the same chromaticity as that of a
given stimulus
Unit: K
Note: The reciprocal colour temperature is
also used, unit K-1 (BE)
Tcase case temperature
The temperature measured at a specified point
on the case of a semiconductor device. Unless
otherwise stated, this temperature is given as
the temperature of the mounting base for
devices with metal can
td
delay time
tf
fall time
The time interval between the upper specified
value and the lower specified value on the trailing edge of the pulse.
Note: It is common to use a 90 % value of the
signal for the upper specified value and a 10 %
value for the lower specified value
Tj
junction temperature
The spatial mean value of the temperature during operation. In the case of phototransistors, it
is mainly the temperature of the collector junction because its inherent temperature is the
maximum
toff
turn-off time
ton
turn-on time
tp
pulse duration
The time interval between the specified value
on the leading edge of the pulse and the specified value an the trailing edge of the output
pulse
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35
Symbols and Terminology
Vishay Semiconductors
Note: In most cases the specified value is 50 %
of the signal
tpi
input pulse duration
tpo
output pulse duration
tr
rise time
The time interval between the lower specified
value and the upper specified value on the trailing edge of the pulse.
Note: It is common to use a 90 % value of the
signal for the upper specified value and a 10 %
value for the lower specified value ts Storage
time
ts
storage time
Tsd soldering temperature
Maximum allowable temperature for soldering
with a specified distance from the case and its
duration
Tstg storage temperature range
The temperature range at which the device
may be stored or transported without any
applied voltage
TXD Electrical data input port of a transceiver device
V
volt
V(O) standard luminous efficiency function for
photopic vision (relative human eye sensitivity)
V(O), V'(O)
spectral luminous efficiency (of a monochromatic radiation of wavelength O); V(O) for photopic vision; V'(O) for scotopic vision)
Ratio of the radiant flux at wavelength Om to
that at wavelength O such that both radiations
produce equally intense luminous sensations
under specified photometric conditions and Om
is chosen so that the maximum value of this
ratio is equal to 1.
VCC supply voltage (positive)
VCEsat collector-emitter saturation voltage
The saturation voltage is the dc voltage
between collector and emitter for specified
(saturation) conditions, i.e., IC and EV (Ee or
IB), whereas the operating point is within the
saturation region
Vdd supply voltage (positive)
VF
forward voltage
The voltage across the diode terminals which
results from the flow of current in the forward
direction
VFIR As SIR, data rate 16 Mbit/s
Vlogic reference voltage for digital data communication ports
VO
output voltage
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36
'VO output voltage change
(differential output voltage)
VOC open circuit voltage
The voltage measured between the photovoltaic cell or photodiode terminals at a specified
irradiance/illuminance (high impedance voltmeter!)
VOH output voltage high
VOL output voltage low
Vph photovoltage
The voltage generated between the photovoltaic cell or photodiode terminals due to irradiation/ illumination
VR
reverse voltage (of a junction)
Applied voltage such that the current flows in
the reverse direction
VR
reverse (breakdown) voltage
The voltage drop which results from the flow of
a defined reverse current
VS
supply voltage
VSS (most negative) supply voltage (in most
cases: Ground)
± M1/2 angle of half transmission distance
K
quantum efficiency
T1/2; ± M = D/2
half – intensity angle
In a radiation diagram, the angle within which
the radiant (or luminous) intensity is greater
than or equal to half of the maximum intensity.
Note: IEC60747-5-1 is using T1/2. In Vishay
data sheets mostly ± M = D/2 is used
T1/2; ± M = D/2
half – sensitivity angle
In a sensitivity diagram, the angle within which
the sensitivity is greater than or equal to half of
the maximum sensitivity.
Note: IEC60747-5-1 is using T1/2. In Vishay
data sheets mostly ± M = D/2 is used
:
solid angle, see sr, steradian for
IEC60050(845)-definition
The space enclosed by rays, which emerge
from a single point and lead to all the points of
a closed curve. If it is assumed that the apex of
the cone formed in this way is the center of a
sphere with radius r and that the cone intersects with the surface of the sphere, then the
size of the surface area (A) of the sphere subtending the cone is a measure of the solid
angle :
: = A/r2
The full sphere is equivalent to 4S sr.
A cone with an angle of D/2 forms a solid angle
Document Number: 82512
Rev. 1.4, 06-Oct-06
Symbols and Terminology
Vishay Semiconductors
of : = 2S(1-cos D/2) = 4Ssin2D/4
Unit: sr (steradian)
Om
wavelength of the maximum of the spectral
luminous efficiency function V(O)
'O
range of spectral bandwidth (50 %)
The range of wavelengths where the spectral
sensitivity or spectral emission remains within
50 % of the maximum value
)e;); P
radiant flux; radiant power
Power emitted, transmitted or received in the
form of radiation.
Unit: W
W = Watt
)v; ) luminous flux
Quantity derived from radiant flux )e by evaluating the radiation according to its action upon
the CIE standard photometric observer. For
photopic vision
)v = Km
f d)
eO
V( O d O
³0 -------------dO
O
Oc
wavelength, general
centroid wavelength
Centroid wavelength Oc of a spectral distribution, which is calculated as "centre of gravity
wavelength" according to
O2
O2
Oc =
³ O Sx ( O d O e ³ Sx ( O d O
O1
OD
Op
O1
dominant wavelength
wavelength of peak sensitivity or peak emission
,
d )eO
where -------------- is the spectral distribution of
dO
the radiant flux and V(O) is the spectral luminous efficiency.
Unit : lm
lm: lumen
Km = 683 lm/W:
Note: For the values of Km (photopic vision)
and K'm (scotopic vision), see IEC60050
(845-01-56).
Document Number: 82512
Rev. 1.4, 06-Oct-06
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37
Symbols and Terminology
Vishay Semiconductors
Ω = 4π sr
α = 65.5°
Ω = 1.0sr
α = 2 arc cos (1 – / 2 π)
α = 20.5°
Ω = 0.01sr
Ω = 0.1sr
α = 6.5°
94 8584
Definitions
Databook Nomenclature
The nomenclature and usage of symbols, abbreviations and terms inside the Vishay Semiconductors
IRDC Databook is based on ISO and IEC standards.
The special optoelectronic terms and definitions are
referring to the IEC Multilingual Dictionary (Electricity,
Electronics and Telecommunications), Fourth edition
(2001-01), IEC50 (Now: IEC60050). The references
are taken from the current editions of IEC60050
(845), IEC60747-5-1 and IEC60747-5-2. Measurement conditions are based on IEC and other international standards and especially guided by
IEC60747-5-3.
Editorial notes: Due to typographical limitations variables cannot be printed in an italics format, which is
usually mandatory. Our databook in general is using
American spelling (AE). International standards are
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38
written in British English (BE). Definitions are copied
without changes from the original text. Therefore
these may contain British spelling.
Radiant and Luminous Quantities and Their Units
These two kinds of quantities have the same basic
symbols, identified respectively, where necessary, by
the subscript e (energy) or v (visual), e.g.)e, )v. See
note.
Note: Photopic and scotopic quantities. - Luminous
(photometric) quantities are of two kinds, those used
for photopic vision and those used for scotopic vision.
The wording of the definitions in the two cases being
almost identical, a single definition is generally sufficient with the appropriate adjective, photopic or
scotopic added where necessary.
The symbols for scotopic quantities are prime
()'v, I'v, etc), but the units are the same in both cases.
Document Number: 82512
Rev. 1.4, 06-Oct-06
Symbols and Terminology
Vishay Semiconductors
The radiometric terms are used to describe the quantities of optical radiation.
The relevant radiometric units are:
In general, optical radiation is measured in radiometric units. Luminous (photometric) units are used when
optical radiation is weighted by the sensitivity of the
human eye, correctly spoken, by the CIE standard
photometric observer (Ideal observer having a relative spectral responsivity curve that conforms to the
V(O) function for photopic vision or to the V'(O) function for scotopic vision, and that complies with the
summation law implied in the definition of luminous
flux).
Note: With a given spectral distribution of a radiometric quantity the equivalent photometric quantity can
be evaluated. However, from photometric units without knowing the radiometric spectral distribution in
general one cannot recover the radiometric quantities.
Radiometric Terms, Quantities and Units
Photometric
Term
Equivalent Radiometric
Term
Radiometric Term
Symbol
Unit
Reference
Radiant power,
Radiant flux
)e
W
IEC50 (845-01-24)
Radiant intensity
Ie
W/sr
IEC50 (845-01-30)
Irradiance
Ee
W/m2
IEC50 (845-01-37)
Radiant Exitance
Me
W/m
2
IEC50 (845-01-47)
Radiance
Le
W/(srm2)
IEC50 (845-01-34)
Table 1: Radiometric Quantities and Units
Photometric Terms, Quantities and Units
The photometric terms are used to describe the quantities of optical radiation in the wavelength range of
visible radiation (generally assumed as the range
Symbol
Unit
Reference
)v: IEC50 (845-01-25)
Luminous power
or
Luminous flux
Radiant power
or
Radiant flux )e
)v
lm
Luminous intensity
Radiant intensity Ie
Iv
lm/sr = cd
Iv: IEC50 (845-01-31)
cd: IEC50 (845-01-50)
Illuminance
Irradiance Ee
Ev
lm/m2 = lx (Lux)
Ev: IEC50 (845-01-38)
lx: IEC50 (845-01-52)
Luminous exitance
Radiant exitance Me
Mv
lm/m2
IEC50 (845-01-48)
Luminance
Radiance Le
Lv
cd/m2
IEC50 (845-01-35)
lm: IEC50 (845-01-51)
Table 2: Photometric Quantities and Units
Photometric units are derived from the radiometric
units by weighting them with a wavelength dependent
standardized human eye sensitivity V(O) - function,
the so-called CIE-standard photometric observer.
There are different functions for photopic vision
(V(O) ) and scotopic vision (V'(O) ).
In the following is shown, how the luminous flux is
derived from the radiant power and its spectral distribution. The equivalent other photometric terms can
be derived from the radiometric terms in the same
way.
9 m2
4 m2
1 m2
1m
2m
3m
Relation between distance r, irradiance (illuminance) Ee (Ev) and intensity Ie (Iv)
The relation between intensity of a source and the
resulting irradiance in the distance r is given by the
basic square root rule law.
An emitted intensity Ie generates in a distance r the
irradiance Ee = Ie/r2.
This relationship is not valid under near field conditions and should be used not below a distance d
smaller than 5 times the emitter source diameter.
Document Number: 82512
Rev. 1.4, 06-Oct-06
18145
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39
Symbols and Terminology
Vishay Semiconductors
Using a single radiation point source, one gets the following relation between the parameter Ee, )e, r:
d )e W
E e = ----------- ------dA m 2
use
d)
A
I e = ------- , : = ----- and get
d:
2
r
I W
d)
d:
E e = ----------e- = I e -------- = ----e ------2
2
dA
dA
r m
Examples
1. Calculate the irradiance with given intensity and
distance r:
Transceivers with specified intensity of
Ie = 100 mW/sr will generate in a distance of 1 m an
irradiance of Ee = 100/12 = 100 mW/m2. In a distance
of 10 m the irradiance would be
Ee = 100/102 = 1 mW/m2.
2. Calculate the range of a system with given intensity
and irradiance threshold.
When the receiver is specified with a sensitivity
threshold irradiance Ee = 20 mW/m2, the transmitter
with an intensity Ie = 120 mW/sr the resulting range
can be calculated as
r =
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40
Ie
=
-----Ee
120
---------- =
20
6 = 2.45 m
Document Number: 82512
Rev. 1.4, 06-Oct-06