General Description of Light Emitting Diodes
General Description
General LED Characteristics
(1) Absolute maximum ratings
Conditions which should never be exceeded to prevent
destruction of the LED and which correlate with the
operating temperature.
(2) Continuous forward current (I
F
), peak forward
current (I
FM
)
Current which causes the LED to emit light. Since the LED
generates a certain amount of heat as current flows which
affects the operating life, the current is limitted by a forward
current derating curve.
(3) Reverse voltage (V
R
)
An LED is a diode designed for its light emitting
characteristics. Unlike ordinary diodes, the reverse voltage
cannot be controlled by changing the concentration of the
PN junction. Therefore, if a 3 V or higher reverse bias is
applied, the addition of a protective circuit is recommended.
(4) Power dissipation (P)
The internal power dissipation of the LED. The life of the
LED lengthens if it is used at a dissipation (junction
temperature) below a certain level (temperature) .
(5) Operating temperature (T
opr
)
Refers to the temperature range including the heat generated
by the device during operation of the LED. Operation under
conditions where damage to the package material does not
occur is recommended.
(6) Storage temperature (T
stg
)
Refers to the temperature range during non-operation of the
LED. Since it is important for the LED package to pass
light, it is not possible to change the content of the filler
material to improve the temperature characteristics like for
IC packages.
(7) Forward voltage (V
F
)
The voltage between electrodes when forward current is
applied to the LED. It differs according to the added
impurities in the crystal material.
(8) Reverse current (I
R
)
The current when reverse voltage is applied. It is
sufficiently small compared to the forward current. It is
recommended that a circuit which applies a reverse bias
should be avoided.
(9) Luminous intensity (I
V
)
Refers to the brightness measured at a distance of one feet
from the light source. Common units are the µcd and mcd.
The magnitude of the numeric value and the apparent
brightness do not necessary correspond. In actuality, it is
necessary to take into account the contrast, luminance and
quantity of light.
(10)Peak emission wavelength (λ), spectrum radiation
bandwidth (∆λ)
These characteristics differ according to the crystal material
and added impurities.
(11)Directive characteristics, Half value of viewing
angle
Represents the directivity dependency of the LED luminous
intensity as a relative luminous intensity value. Generally,
the luminous intensity is highest along the normal optical
axis and decreases as the angle with respect to the optical
axis increases. The angle at which the luminous intensity
drops to 50% of the peak value is called the halfpower
angle. It can be used as a guide showing the sharpness of the
directivity.
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