Posts Tagged ‘LUX METER’


May 23rd, 2014

Lux is a measurement of the overall intensity of light within an environment for any given area or distance from the source or lux is the amount of light in an environments perceived by the human eye. Quality of light in workplace, schools and public buildings affect the quantity and quality of performance in workers and students.

In other words, the lux is a unit of measurement of brightness, or more accurately, illuminance. The illumination is how level of luminous flux is falling on a surface area. The luminous flux is visible component that is defined in radiant flux (light power) divided by relative sensitivity of human eyes over the visible spectrum. This means the Lux is well fit to light level from sense of human eyes. Lux is ultimately derives from the candela, the standard unit of measurement for the power of light.

A candela is a fixed amount, roughly equivalent to the brightness of one candle.While the candela is a unit of energy, it has an equivalent unit known as the lumen, which measures the same light in terms of its perception by the human eye. One lumen is equivalent to the light produced in one direction from a light source rated at one candela. The lux takes into account the surface area over which this light is spread, which affects how bright it appears. One lux equals one lumen of light spread across a surface one square meter.

How to Measure Lighting Levels

Measuring lighting or the illumination of an environment requires the use of an incident Lux meter or foot-candlemeter A lux meter is a device for measuring brightness. It specifically measures the intensity with which the brightness appears to the human eye. This is different than measurements of the actual light energy produced by or reflected from an object or light source.

A lux meter works by using a photo cell to capture light. The meter then converts this light to an electrical current. Measuring this current allows the device to calculate the lux value of the light it captured.

The lux light meter’s calculation of illuminance is done by using the Point Source process.  The measure of the lux light meter varies depending on the light’s intensity and distance.  If a point source has no reflections, a portion of the produced light reaches a surface.

How to measure light intensity using lux light meter

  • Compute for the square of the distance and multiply it by Pi and then by four.  The outcome must be a radius identical to the specific space from the source.  This calculation is the area of sphere at a particular distance.
  • Divide the light concentration in lumens by the spherical area. The product is the illuminance in foot-candles or lux, depending on whether feet or meters were used.
  • Application of a correction factor is needed if the light reaches the surface at an angle less than 90 degrees.  This can be done by multiplying the computed illuminance value by the cosine of the off-axis angle.

Applications of Lux meter

i) Photography and Video Filming. By measuring the light in luxes, photographers can adjust their shutter speed and depth of field to get the best picture quality. The device can also be very useful for filming outdoor scenes of television programs or movies as it allows adjustments to make sure scenes filmed in different light levels have a consistent brightness on screen.

ii) Health and Safety regulations : It can be used to check whether the brightness of a room is enough to meet any rules designed to protect workers from suffering damage to their eyesight. Using a lux meter takes into account the size of the room in a way that simply measuring the intensity of the light source in lumens would not.

iii) Photographic Mesurements; It also measures the photography subject’s illuminance.  When using a lux light meter, the photographer can determine the aperture number and the exposure setting.

Types of Lux Light Meters for the photography

  • Reflected Lux Light Meter

i)         This produces a measurement of the light reflecting from the photography subject to the camera

ii)       This kind of meter is positioned near or in the camera itself

iii)      A type of meter that is commonly installed in camcorders and point-and-shoot camera

iv)     Works best for scenes where light is evenly distributed

v)       May not work for scenes with varying brightness

  • Incident Lux Light Meter

i)         This type of lux light meter must be positioned near the photography subject

ii)       Measures the light intensity falling on the photography subject

iii)      Will produce great light reading when used with light receptor facing the camera

iv)     A photographer may produce trial shots before working on the desired camera settings.

Safety Guideline

  • In case of digital Lux meter, it is necessary to replace battery when the meter shows battery low.
  • The meter should ever not be placed in water deep enough to submerge any part of the upper body of the meter. this will ruin the meter.
  • Do not store the instrument where temperature or humidity is excessively high.
  • The measurement points should not be too close to walls or obstructions
  • Daylight should be shielded by blinds or curtains when assessing artificial lighting only