Because near-infrared beams are invisible to the naked eye, a means of locating the beam is often required to align it with an infrared detector. By placing the card at the emitter so that the beam impinges on the card's active phosphor surface the beam should be highly visible. Then, move the card away from the card in the apparent direction of the beam. In this way, the invisible laser beam can be located at far distances from the emitter (and specifically, at the detector). If the beam diverges rapidly, then, of course, the beam-finder card is less useful at the distance when the beam size exceeds the active diameter of the card.

A beam-finder card is a replacement for an infrared viewer when one needs to check if an IR emitter is operational or to locate the primary beam of emission from an IR source. However, if locating stray beams is desired or if the beams are lower power, an IR Viewer may be the required solution.