This experiment uses the ability of chargeable IR indicators to store light energy to detect a single light incidence which results, for example, when someone is looking into foreign cupboards without permission.

Required equipment

• Powerful IR source (e.g. halogen lamp)
• IR permeable filter for blocking visible and UV light
• IR indicator: IRI 1100
• Light-tight box for IRI 1100
• Deep red lamp for darkrooms or LED lamp
• Powerful 950 nm IR LED (e.g. LD 242-2 from Siemens)

Safety measures

Preparation: Discharging

1. Equip halogen lamp with IR filter.
2. Prepare light-tight box for IRI 1100.
3. Darken the room completely (deep red light without parts below 600 nm wavelength is allowed).
4. Expose the active surface of the IRI 1100 to IR radiation until orange emission disappears completely (can be detected only with 950 nm LED. Inspite of filtering, the halogen lamp contains still too much dark red parts (which contribue to the discharging but are still visible)). The discharging may take several minutes unto several hours!
5. Enclose IRI 1100 in light-tight box.

Realization and analysis

1. Remove the IRI 1100 from the box (in darkness!) and put it at the place that has to be secured (e.g. light-tight cupboard).
2. After the end of the observation time (e.g. some days) enclose IRI 1100 again in light-tight box (in darkness).
3. Test, in complete darkness, with 950 nm LED whether any orange emission is detectable. If so, the cupboard has been opened. Incident light has charged the IRI 1100. From the intensity of charging, conclusions may be drawn about the time of exposure to incident light.