Forward Current vs Ambient Temperature
Figures 1 and 2 show an example of in which the current is derated to take temperature into account. Toshiba technical data for LED lamp usually shows the permissible current values against temperature. Refer to this information when planning a new design.
The following example describes how to derate for temperature when designing:
Figure 1 - Specified by design (22 mA) exceeds permissible value at high temperatures
Figure 2 - Specified by design (22 ma) is within permissible value at high temperaturesLED Lamp
Derating for Longevity
Characteristically, the luminous intensity of LEDs gradually decreases over the life of the LED. The rate at which the luminous intensity falls varies according to the material used and the forward current the LED is driven at. The larger the current, the greater the diminution of luminosity. Thus, when setting the forward current of the LED lamp, do not determine the setting solely from the temperature characteristics, as in the above example, but consider also longevity characteristics. An effective way of improving the longevity characteristics is to set the forward current of the LED lamp relatively low.
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