Figure 3.9 Typical Reverse Current versus
Reverse Voltage for HPWA-xHOO LED Emitter
(Linear Scale).
Figure 3.10 Typical Luminous Flux versus
Forward Current for HPWA-xHOO LED Emitter
(Logarithmic Scale).
At 85°C, the light output will be approximately
50% of the light output at 25°C. At –40°C, the
light output will be approximately twice the light
output at 25°C. This change is fully reversible.
and dominant wavelength over temperature are
fully reversible when the ambient temperature
returns to 25ºC.
As might be expected, the junction temperature
varies directly as a function of ambient
The peak and dominant wavelength of an
AlInGaP LED emitter changes by about 0.1 nm
per ºC. Thus, the color of the LED shifts slightly
toward the red at elevated temperatures.
temperature. In addition, the junction
temperature of the LED emitter is hotter than the
surrounding ambient temperature due to the
internal power dissipation (IFVF) within the LED
emitter. Figure 3.13 shows the internal
By now, it should be apparent that a number of
the electrical and optical characteristics of an
LED emitter vary as a function of ambient and
junction temperature. All of these changes in
forward voltage, luminous intensity, and peak
temperature rise, TJ – TA, for an LED signal lamp
over a range of thermal resistance, as a function
of the forward current through the LED emitter.
Figure 3.11 Expected Variations in Luminous Flux
versus Forward Current for HPWT-xHOO LED
Emitters (Logarithmic Scale).
Figure 3.12 Typical Luminous Flux versus
Temperature for HPWT-xHOO LED Emitter
Driven at 60 mA (Linear Scale).
15
LUMILEDS [ LUMILEDS LIGHTING COMPANY ]
