There are lots of units of measure for Light and many different types and terms. In this post I hope to explain a little bit about how our meters here work and what they were designed to do.

Extech Light Meters measure Illuminance. The units that Extech Light Meters measure and display in are Footcandles and Lux.

ILLUMINANCE is a measure of the amount of light falling on a surface. It is defined as: 'the density of the luminous flux incident on a surface'. It is the quotient of the luminous flux by the area of the surface when the latter is uniformly illuminated.  - (E = df / dA)

One footcandle is the illuminance at a point on a surface which is one foot from, and perpendicular to, a uniform point source of one candela. One lux is the illuminance at the same point at a distance of 1 meter from the source. One lumen uniformly distributed over one square foot of surface provides an illumination of 1 footcandle.

If you work in feet, your results will be in footcandles - (1 footcandle = 1 lumen/square ft.)
If you work in meters, your results will be in lux - (1 lux = 1 lumen/square meter) The relationship between Lux and Footcandles are about 1 to 10 (1 footcandle = 10.763 910 4 lux).

Ok,  Enough with the technical jargon.Typically you will find people using Light meters to make sure there is enough lighting in an area where there needs to be. If the proper level of Light does not exist then it could be a Safety issue. Classrooms, Offices, ATMs, Parking Garages, Sports Venues are just some of the places where Light should be checked periodically to ensure the proper levels exist. Extech offers many different models with different features, accuracies and resolutions. Choosing the proper model for the job requires some knowledge of what you are testing for, and what level should be present. This can usually be found in an ordinance or testing procedure that you go by when preforming your tests. One of the most common governing body for safety is OSHA and you can probably find info on their website at: http://www.osha.gov/ Extech meters cannot be used on colored LED Lights or Ultraviolet Lighting. The results could result in inaccuracies as this type of light is outside of the spectrum the CIE sensor can handle. I hope the info is helpful.