Light Meter

 

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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