Lumen = Luminous Flux (lm)


Lumen is the international (SL) unit of luminous flux, a measure of overall light emitted by a light source.

SI unit
Luminous flux
lumen (= cd sr)
also called luminous power

Candela = Luminous Intensity (cd)


Candela is the international (SL) unit of luminous intensity, a measure of light emitted by a light source in a particular direction. Any given light source will have different luminous intensities in different directions considered.

SI unit
Luminous intensity
candela (= lm/sr)
an SI base unit
candela per square metre

Beam Angle (Unit: degree)


Beam angle is the angle between two directions for which the luminous intensity is 50% of the maximum intensity as measured in a plan through the nominal beam centreline. Beam angle of a bulb gives an idea of how the light beam spreads away from the beam centre.

LUX = Illuminence (lx)


Lux is the international (SL) unit of illuminance, a measure of light arriving at a surface, 1 lumen per square foot equals 1 foot-candle, while 1 lumen per square meter equals 1 lux. [lux = lumen/m2]

SI unit
lux (= lm/m2)
Used for light incident on a surface
Luminous emittance
lux (= lm/m2)
Used for light emitted from a surface

Colour Temperature/Correlated Colour Temperature (CCT)

CRIA black-Body radiator will have a different colour when it is heated up to different temperatures (in kelvin). The Temperature at which the heated black-body radiator matches the colour of the light source is the colour temperature of the light source.


Not all lighting products are designed for dimming function. Dimming a non-dimmable LED lighting product will cause un-predictable result and may affect the life time of the products.

Colour Rendering Index (CRI)


Colour rendering index ranges from 0-100 ,measures a light source’s ability to reproduce the colour of various objects being lit by a reference light source, black body radiator(CRI=100). (This is generally considered inversely proportional to the Colour temperature.) Note: for LED light sources the warmer the colour temperature the more natural skin colour is achieved. (A colour temperature of 2700K is closest to output of a typical 50W halogen or incandescent globe. The cooler the colour temperature the more blue/grey skin colour becomes).

Efficacy = Efficiency (lm/W)


Efficacy is the efficiency of a light source to concert electricity energy to light energy which is expressed in lumen output per unit power input (watt)

[Efficacy = lumen / wattage]

Cone Diagram

Cone-diagramThis diagram gives the lux output level and dispersion from a given light source with a specific beam angle. This can be used to assess basic lux level achieved from a light source at a specific distance from that source. (e.g. from the diagram below you will note at 2m from the light source an average lux level of 112.91 is present over an area of 2.0118m)

Halogen VS Lumex LED


An Energy Monitor was used to record power consumption on a homes lighting circuit prior to the replacement of traditional halogen downlights with energy efficient Lumex 11W LED downlights. The results clearly show that Lumex LED Lighting generate an 80% energy saving.

Design Life Time/Lumen Maintenance (maintained lumens)

Product-Life-Time-comparisonThe effective loss or depreciation of lumen output of a light source over time. Design life time is the average life of a lighting product when it is operated at nominal lamp voltage, current and controlled working environment. Actual lamp life varies because of any different from those rating condition. LM70: A reference used by the IESNA, in its Energy Star rating process and relates to the point where the light source has deteriorated to 70% of its original rated lumen output. (In critical installations this is the point where light source replacement is considered).

Visual field (1), preferred visual field (2) and optimum field of vision (3) of a person standing and sitting for vertical visual tasks. Preferred field of vision for horizontal visual tasks. Preferred angle of 25%

The value of any particular information relates to the current activity of the observer. This activity may be work or movement-related or any other activity for which visual information is required. Lighting conditions under which the visual task can be perceived to an optimum degree can be determined from the above-motioned-specific features. It is possible to define ways of lighting which will be ideal for specific activities.