Characteristics of IREDs

Characteristics of IREDs Measurement of Power Output It is standard industry practice to characterize the output of IREDs in terms of power output. Since the amount of light an IRED generates depends on the value of the forward drive current (IF), the power output is always stated for a given value of current. Also, the ambient temperature must be specified inasmuch as the radiant power decreases with increasing temperature, power decreases with increasing temperature, typically °C. The following two methods are used to measure light power output. front of the IRED. In order to achieve repeatable and meaningful measurement of this parameter. | Characteristics of IREDs Measurement of Power Output It is standard industry practice to characterize the output of IREDs in terms of power output. Since the amount of light an IRED generates depends on the value of the forward drive current IF the power output is always stated for a given value of current. Also the ambient temperature must be specified inasmuch as the radiant power decreases with increasing temperature power decreases with increasing temperature typically C. The following two methods are used to measure light power output. Total Power PO This method involves collecting and measuring the total amount of light emitted from the IRED regardless of the direction. This measurement is usually done by using an integrating sphere or by placing a very large area detector directly in front of the IRED so that all light emitted in the forward direction is collected. The total output power is measured in units of watts. The total power method ignores the effect of the beam pattern produced by the IRED package. It cannot predict how much light will strike an object positioned some distance in front of the IRED. This information is vital for design calculations in many applications. However total output power measurement is repeatable and quite useful when trying to compare the relative performance of devices in the same type of package. DETECTOR Detector is so large in area and is so close to the IRED that all light emitted by the IRED is collected. Measuring Total Power - All Light is Collected On Axis Power PA This method characterizes the IRED in terms of axial intensity. Many practical applications require knowledge of what percentage of IR power emitted is incident upon a detector located at some distance in front of the IRED. In order to achieve repeatable and meaningful measurement of this parameter it is necessary that the distance from the IRED to the detector and the active area of the detector be specified. This is because the radiation pattern

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