Experiment 02 with IR indicators:

Direct detection of 950 nm LED radiation

This experiment describes the fundamental application of the IR indicators IRI 1100 and IRI 4400 for testing 950 nm IR LEDs.

Required equipment

IR source: 950 nm LED (eg Siemens LD 242-2, LD 274, SFH 409)
IR indicator: IRI 1100 or IRI 4400
Daylight source (only IRI 1100)

Safety measures

none

Preparation: Charging

Expose IRI 1100 to daylight or fluorescent light prior to use (charge). The charging time depends on the intensity of the exciting light. Normally, it takes less than a minute. Important is the blue part of the charging light. Incandescent bulbs are inappropriate because of their high IR level. They would discharge the card simultaneously during charging. The IRI 4400 needs no charging.

Realization: IR detecting

Hold the active surface of the IR indicator card near the light emitting diode (operating with approx. 50 mA) with ambient light shielded. If there is IR radiation, the active surface will emit a visible light (IRI 1100: orange; IRI 4400: green). As soon as the IR stimulated emission drops (IRI 1100), recharge as described above. The green emission of the IRI 4400 having a square law dependency from the radiation density of the IR source, the active area of this card has to be brought as near as possible to the LED surface. Best results are obtained with LD 242, which work with a current up to 300 mA (cooler needed!).