Editing Light meter (section)

== Other uses ==

In Scientific Research & Development uses, a light meter consists of a [[radiometer]] (the electronics/readout), a photo-diode or sensor (generates an output when exposed to electromagnetic radiation/light) a filter (used to modify the incoming light so only the desired portion of incoming radiation reaches the sensor) and a cosine correcting input optic (assures the sensor can see the light coming in from all directions accurately).

When the word light meter or photometer is used in place of radiometer or optometer, or it is often assumed the system was configured to see only visible light. Visible light sensors are often called illuminance or photometric sensors because they have been filtered to be sensitive only to 400-700 nanometers (nm) mimicking the human eyes' sensitivity to light. How accurately the meter measures often depends on how well the filtration matches the human eyes' response.

The sensor will send a signal to the meter that is proportional to the amount of light that reaches the sensor after being collected by the optics and passing through the filter. The meter then converts the incoming signal (typically current or voltage) from the sensor into a reading of calibrated units such as Foot-Candles (fc) or Lux (lm/m^2). Calibration in fc or lux, is the second most important feature of a light meter. It not only converts the signal from V or mA, but it also provides accuracy and unit to unit repeatability. [[National Institute of Standards and Technology]] (NIST) traceability and [[ISO/IEC 17025]] accreditation are two well known terms that verify the system includes a valid calibration.

The meter/radiometer/photometer portion may have many features including:

'''Zero:''' subtracts ambient/background light levels, or stabilize the meter to the working environment

'''Hold:''' freezes the value on the display.

'''Range:''' for systems that are not linear and auto ranging this function allows the user to select the portion of the meter electronics that best handles the signal level in use.

'''Units:''' For illuminance the units are typically only lux and foot-candles but many light meters can also be used for UV, VIS and IR applications so the readout could change to W/cm^2, candela, Watts etc.

'''Integrate:''' sums up the values into a dose or exposure level i.e. lux*sec or J/cm^2.

Along with having a variety of features, a light meter may also be usable for a variety of applications. These may include the measurement of other bands of light such UVA, UVB, UVC and Near IR.  For example, UVA and UVB light meters are used for phototherapy or treatment of skin conditions, germicidal radiometers are used for measuring the UVC level from lamps used for disinfection and sterilization, luminance meters are used to measure the brightness of a sign, display or exit sign, PAR quantum sensors are used to measure how much of a given light source's emission will help plants grow, and UV-curing radiometers test how much of the lights emission is effective for hardening a glue, plastic, or protective coating.
  
Some light meters also have the ability to provide a readout in many different units.  Lux and footcandles are the common units for visible light, but so are Candelas, Lumens, and Candela per square meter.  In the realm of disinfection, UVC is typically measured in watts per square centimeter, or watts for a given individual lamp assembly, whereas systems used in the context of the curing of coatings often provide readouts in Joules per Square centimeter.  Regular measurements of UVC light intensity thus can serve to provide assurance of proper disinfection of water and food-preparation surfaces, or reliable coating hardness in painted products.
  
Although a light meter can take the form of a very simple handheld tool with one-button operation, there are also many advanced light-measurement systems available for use in numerous different applications.  These can be incorporated into automated systems that can, for example, wipe lamps clean when a certain reduction in output is detected, or that can trigger an alarm when lamp-failure occurs.