ELSEC 775 / 775C UNIVERSAL LIGHT METER
The ELSEC 775/775C Light Meter replaces 4 separate instruments. This single instrument enables measurement of four parameters that cause damage to buildings, valuable objects, documents etc: ultra-violet and visible light, thermal radiation (infra red) and temperature.
EASE OF USE
Extra care has been taken to make the 775 and the 775C as easy to use as possible. Anyone can take measurements straight out of the box with little, if any, reference to the instruction manual. The appropriate button is pushed depending on the measurement required and the reading is taken. The unit automatically turns off 20 seconds after the last reading unless a button is held down for over 3 seconds, this causes continuous measurements to be taken until another button is pressed. The large OLED display enables an easy to use menu system to select the more advanced functions, change units etc.
The optional data-logging function (type 775C) enables over 73,000 readings of all four parameters to be automatically taken at selectable intervals (every 10 seconds to 1 hour). The saved data can then be transferred to a computer by a standard USB interface. The 775C behaves like a "flash disk", when it is plugged into a PC and it is automatically recognized without any special PC software. When logging data the 775C can be turned off to save power and the built in clock will turn the unit on whenever a reading needs to be taken, this enables a 775C to be left taking readings for months at a time. Software is provided to display the measurements as graphs or text. Data is saved in CSV format that can be accessed and displayed by many programs (e.g. Microsoft Excel).
THERMAL RADIATION (IR)
The measurement of thermal radiation (shown as W/M2) allows the user to estimate how much solar heat is coming through windows, check the performance of heat reflecting films, measure the heating effect of lamps on objects etc.
The amount of visible light is important, not only to check illumination in work areas, galleries etc. but also to control damage to light sensitive objects that is also caused by normal light. Measurements can be displayed as Lux or Foot-candles.
For many years it has been recognized that one of the major causes of damage to museum objects and other sensitive objects, soft furnishings etc. is the fading and rotting effect of light on the object. The most damaging part of the illumination is its ultraviolet content. Since 1976 Littlemore Scientific (ELSEC) has been providing instruments that enable the conservator to measure the UV content of light and thereby protect valuable exhibits. Using the 775, measurements can be taken of the proportion of UV present (mW/lumen), the total amount of UV (mW/M2).
UNITS OF MEASUREMENT FOR UV)
Traditionally UV has been measured in museums as the proportion of ultraviolet present. This result is useful for checking a particular lamp or window because the proportion of UV does not change with the distance from the light source. Using a simple rule, the amount of UV on an object can be limited (it is usual to arrange that the proportion of UV should not exceed 75mW/lumen in museums). The damage is done by the total amount of UV falling on the object, so it is useful to be able to measure this directly, especially if non-standard amounts of illumination are required. The amount of UV should be as little as possible but in general should not exceed 20mW/M2.