As a converting IR indicator card, the green emission of the IRI 4400 obeys a square law dependence from the IR intensity. For higher IR intensities a second emission color can be noticed; its luminosity increases with a power of 2.8.

Required equipment

• IR source: 950 nm high power LED (e.g. TIES 16A from Texas Optoelectronics, LD 242-2 from Siemens)
• Controllable current source or voltage source with series resistance for high-power LED
• IR indicator: IRI 4400
• Red-green stereo glasses (alternatively, a prism or a Compact Disc)

Safety measures

Preparation: installation

Realization

1. Wear red-green glasses and observe LED alternating through red and green filter.
2. Increase current, starting at zero, slowly to maximum level (2 A for TIES 16A and shortly 300 mA for LD 242-2). First, the green emission starts at 540 nm. Then, at higher currents, a red part (660 nm) quickly becomes stronger. The visual color impression somehow turns to yellow at higher IR intensities.
3. With the aid of a prism or a CD (that can be 'misused' as diffraction grid) it can be proved that the IRI 4400 does not create a continuous spectrum containing the colors green and red but a discrete spectrum with two colors, green and red: holding the CD in complete darkness in the correct angle, a red spot appears clearly separated from the green one.