T 1.14 Loss of data due to strong light

Typical optical storage media include CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-R, DVD+R, DVD-RAM, DVD-RW, and MO data media. Information is read and written using a laser, except in the case of MO media, which are written magnetically and read optically. These types of data media are sensitive to strong light, and especially to UV light, and therefore should not be exposed to such sources of light.

The amount of data lost due to light depends on the strength and duration of exposure. This is particularly critical for files which, due to their internal formatting, are rendered completely useless even when the changes are minor (e.g. postscript files, databases, or encrypted files).

Examples of strong light sources include the following:

• sunlight (especially on clear summer days or at high altitudes),
• halogen lamps,
• certain types of fluorescent lamps.

Recent studies have shown that the seriousness of the impact of sunlight or other sources of UV light differs depending on the type of optical storage medium. In the case of commercially duplicated CD/DVD-ROMs, this impact can be considered negligible. In the case of write-once data media (CD-R, DVD-R, DVD+R), though, exposure to direct sunlight for a longer period of time will cause damage because it can change the optical properties of the recording layer. Light only has a minor effect on rewritable optical storage media such as CD/DVD-RWs. Most of the damage caused to these types of data media is due to the heat generated by direct sunlight.