How Light Meters Work

Most meters consist of a body. a photo cell has energy. This energy is transferred by the photo cell into electric current; the amount of current generated depends on the amount of light striking the cell. The meter then reads the electrical current and calculates the appropriate value of either Lux or foot-candles.

A key thing to remember about light is that it is usually made up of many different types (colors) of light at diffrent wavelengths. The reading, therefore, is a result of the combined effects of all the wavelengths. A standard color can be referred to as color temperature and is expressed in degress Kelvin. The standard color temperature for calibration of most light meters is 2856 degrees Kelvin which is more yellow than pure white.

Different types of buids burn at different color temperatures. Sper Scientific meter readings will, therefore, vary with different light sources of the same intensity. This is why some lights seem "harsher" than others. See the chart to the left for suggested lighting levels for various applications.

Light Meter Units of Measure

Light can be quantified in many ways, i.e., Lux, Lumens, foot-candles,candle power, candelas, and so on. The two most popular scales are Lux, which is the European measure,and foot-candles, which is the U.S. scale. Lux is a unit of illumination of one square meter which is one meter away from a uniform light source. 1 candela = 1 Lux. Foot candles are a unit of illumination of one square foot which is one foot away from a uniform light source. 

Light Measurement Conversion Factor

Abbreviations:
FC-Footcandle, Lux-Lux, Lumen-Lumen

Since: 1 Lumen/sq ft, and 1 Lux=1 Lumen/sq meter
and: 1 square ft=0.0929 sq meter
then: 1 Lux=0.0929 FC, and 1 FC=10.76 Lux

All models have a fast and accurate response, and are CE approved. The sensors are cosine and color corrected and hermetically sealed to ensure long term stabillty. These meters come ready to use with probes, 9V battery, carrying case, instructions, and a 5-year warranty.

Convenient Lighting Levels for Varying Applications
Offices
100 to 300	Lux	General workrooms, corridors, stairs and restrooms
300 to 750	Lux	Conference and computer rooms
750 to 1500	Lux	Technical offices, rooms for drawing and calculating
Factories
300 to 750	Lux		Winding, steel work and welding
750 to 1500	Lux		Inspection, welding, heavy machinery operation
1500 to 3000	Lux		Inspection and testing operations, selection areas, machine tool areas
Schools
75 to 300	Lux		Lecture rooms, assembly halls, corridors, stairs and toilets
200 to 750	Lux		Classrooms, demonstration rooms, gymnastics
300 to 1500	Lux		Precision drawing rooms, experimental laboratories, libraries and reading rooms
Shops
120 to 500	Lux		Stairs, elevators, toilets and corridors
500 to 1000	Lux		Display windows and sales areas
4000 to 8000	Lux		Jewelers and goldsmiths

 

 

 

 

 

 

 

 

 

 

 

 

Sper Scientific light meters have been checked and calebrated using NIST traceable light sources and standards. The light source is a color correct buid that burns at 2856 degrees Kilvin. The meters have a 5-year warranty. they are used in many applications, from testing the reflectance of porcelain pigments in a QC lab to pharmaceutical degradation studies.

To convert from	into	multiply by
Lux	Candela steradian	1.0
Lumens	Candle power (spherical)	0.07958
Lumens	Watts	0.0015
Lumens per square centimeter	Lamberts	1.0
Lumens per square centimeter	Lux	10000
Lumens per square centimeter	Phots	1.0
Lumens per square foot	Foot candles	1.0
Lumens per square foot	Foot lamberts	1.0
Lumens per square foot	Lumens /Square meter	10.76391
Lumens per square foot	Lux	10.76396
Lumens per square meter	Foot candles	0.0929
Lumens per square meter	Lumens/Square foot	0.0929
Lumens per square meter	Phots	0.0001
Lumens per square meter	Lux	1.0
Lux	Foot Candles	0.0929
Lux	Lumens/square meter	1.0
Lux	Phots	0.0001

 

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