The ability to read the level of light is critical for the preservation of light sensitive materials. APS's light meter features a convenient remote sensor and microprocessor to provide excellent accuracy and convenience of use.

The large digital LCD reads in either foot-candles or lux. The instrument measures in three ranges for maximum resolution. The three ranges are:

• 0-20 foot-candles (0-200 lux)
• 0-200 foot-candles (0-2,000 lux)
• 0-2000 foot-candles (0-20,000 lux)

In any range, if the intensity surpasses the ability of the instrument, a reading of "0L" will be shown; selecting the next highest range will yield a proper reading. All instruments are calibrated over all three ranges.

This single instrument provides measurement of the four environmental parameters that are of most frequent interest to conservators and museum professionals.

• Ultraviolet (UV is measured in units of �W/lumen and mW/M�)
• Visible light (Lux or Foot-candles)
• % Relative Humidity [and Dew point]
• Temperature (�C or �F)

Units of Measurement for UV
Traditionally, UV has been measured in museums as the proportion of ultraviolet to visible light. This proportional value is useful for checking the efficiency of a particular lamp or window in terms of UV output, regardless of the distance from the source where the reading was taken. This is because the proportion of UV to visible light does not change with the distance from the light source. The standard UV meter, which only reads absolute amount of UV energy, is inappropriate for most museum applications. The Elsec 764 UV meter, which reads the proportion of UV to visible light, is designed specifically for the unique needs of the museum community.