Lightproofing

Lightproofing is the practice of preventing light from entering or escaping a space or enclosure. It is used to protect sensitive materials from unintended illumination, to ensure true darkness for imaging or experiments, and to minimize light pollution in enclosed environments. Lightproofing focuses on eliminating both direct light paths and indirect reflections, using a combination of materials and assembly techniques.

Common methods include sealing gaps around doors and windows with weatherstripping and door sweeps, installing opaque window coverings such as blackout curtains or blinds, and applying light-blocking films or paints. Internal reflectance can be reduced by lining walls with matte, light-absorbing materials. For penetrations such as cables or vents, grommets, light-tight cable glands, and light traps are used. In practice, a space may also be fitted with removable liners or blackout enclosures for temporary needs. Fire safety, ventilation, and electrical codes should guide material choices, since some blackout fabrics or coatings may affect heat dissipation or flame spread.

Applications span photography darkrooms, astronomical observatories, laboratories handling photosensitive reagents, museums and archives, display cases, theaters, and greenhouses or plant facilities where precise photoperiods are required.

Measurement and verification are typically done with a light meter or lux meter under expected conditions. A space is considered adequately lightproof when light transmission is reduced to near zero outside of intentional lighting, and any leaks are identified and mitigated.