Terms related to Lighting and Lighting fixtures ..

Luminous flux of luminarie (Light fitting or bulb)

Luminous flux is total light output emitted by luminarie. It is denoted by  (Φ) or lumen or lm.

Light emitted by a light fitting, Lumen decreases with the distance from that light fitting.


Illuminance or Lux is light density means light falling on a sq.meter surface by a light fitting . Its unit is lumen/square meter or lumen/square feet.

It is most widely used term in light..lighting design is done by keeping proper lux in each area ..for example, a workplace need more lighting than common area.


It is generally efficiency of a luminarie. All you know, efficiency is ratio of output to input . So efficacy will be lm/watt, where lm is lumnious flux output and watt is input power consumed.

Correlated Colour temperature (CCT)

Suppose a LED light has colour temperature of 3000 K what it means ??

It means LED light gives warm white light as output.

Actually colour of a light is given by temperature range from 1000-10,000 Kelvin(K).

Kindly note that colour temperature of a light or lamp does not mean it will operate at that temperature ..it only mean that it will give colour similar to a metal when metal is heated ay cour temperature value.

Colour Rendering Index(CRI)

Colour Rendering means the deviation of colour of a object under artificial electrical light from the colour of the object under the Sun.

CRI value is from zero to 100. a value of 100 indicates that a artificial electrical light will give object its true colour.

Incandescent lamps are CRI of 100.

  • 0-55 CRI value – Poor
  • Upto 90 – Good
  • Above 90 – best


This test LM80 gives the age or lifetime of LED modules used inside LEd bulb and Luminaries. LM80=60,000 means after 60,000 hours of operation of LED module, LED module lumnious flux ( or simple light from LED module) will only left 80 percent of the intitial light output or luminous flux.

LED lights does not fail at once ..their lighting output fall over time ..as they are composed of many LED modules and LEDs in LED modules will slowly slowly give less output ..this test tell you that ..

Generally LED manufactures gives LM80 value at 25 degree ambient temperature ..

The test is developed and approved by Illumanating Engineering Society of North America (IESNA).

As the test is developed and approved by IESNA so this test is conducted using IESNA approved test procedure and test equipment.

One more thing, you have seen LM values LM80= 50,000 hours or 60,000 hours.

So the question is …does the lab test a light for 50,000 hours or 60,000 hours ??

The answer is a big No ??

Test is conducted for 10,000 test hours and fall in lumnious flux of module is noted after each 1000 hours ..and a graph is drawn betwen Light output and test hours..

And for 6 times the test hours (60,000 hours), fall in lumnious flux is find out by extending this graphical realation.

So how this extending of graphical realation is done ..it is done by a standard TM-21, developed by IESNA.

Kindly note that this test is on LED module , not LED light (luminaries and bulb) so it is conducted by original LED manufactures , not light manufacturers ..


LM 70 is similar to LM80 ..both give life time of LED light ..

LM70=50,000 hours.. means after 50,000 hours , light output of LED module will only be 70 percent of initial Light output.

It is also given generally at ambient temperature of 25 degree.

Kindly note that this test is on LED module , not LED light (luminaries and bulb) so it is conducted by original LED manufactures , not light manufacturers ..

LM79(Lumen Maintenance)

LM79 is a test that is conducted on soild state lighting (LED lamps and luminaries) to find out electrical and photometric properties of LED lights ..

This test LM-79-08 is approved by Illumanating Engineering Society of North America (IESNA) and most of the world and LED manufactures has adopted this standard.

Electrical and photometric properties include the following :

  • Total light output (luminous flux)
  • Efficacy (lm/w)
  • Colour properties like CRI, CCT
  • Luminous intensity distribution
  • Electrical parameters like Power, current , power factor

As the test is developed and approved by IESNA so this test is conducted using IESNA approved test procedure and test equipment.

LED tubelight (T5, T8, T10, T12)

T5 means LED tubelight having (5/8) inch diameter .. similarly T8 means (8/8)=1 inch dia tube and same for T10 and T12.


Bollard picture

See the picture above. This is bollard. It is just like a pole or post with a light on top. It is used for outdoor lighting.

Daylight harvesting

Daylight harvesting means design lighting of a building or a room in auch a way that maximum sunlight ⛅ cab be used and electricity consumption can be reduced.

Diffuser/Diffused light

Generally a piece of glass or acrylic is placed inside luminarie to distribute light uniform and without glare..this piece of glass or acrylic is called diffuser.


A light fitting or luminarie that direct it light downwards


Dimmer is a switch that looks like fan regulator ..only difference is that it has no step and used to control a light fitting output.

Incandescent bulb

You all have seen above pic in your home. This is incandescent bulb. It has tungsten filament .when current flows through filament .it becomes hot and gives light.


All LED lights have driver ..in our home and offices , type of Electrical supply available is AC . The driver convers this AC supply to DC as LED module works on DC.

Driver can be built in inside LED light or fitted externally.


A light fitting has many components like LED module, driver, diffuser and external housing..complete assembly is called luminarie.

Emergency lighting

Some lights are provided that runs when normal light from electric company fails ..it may be portable rechargeable light or DC lights on ceilings, walls.

Ingress Protection (IP) rating or Number

Ingress Protection Number or rating is a two digit number .this 2 digit number tells how well a light fitting or luminarie are protected from dust or soild particles and moisture/water.

IP Rating

Impact Protection (IK) Number or Rating

Impact Protection number or rating is given to a light fitting ..number given is from 0 to 10. This number gives how well a light fitting protected from a mechanical impact or shock.. a IK value of 10 means light fitting is vandal proof.

IK rating

Vandal proof lights are installed in public places to avoid vandalisation.

Solid state lighting

The light fitting which uses semi conductor components to produce light ..for example, LED lights are solid state lighting.

Flood light

Flood light means flood of light …means a light fitting which gives high value of luminous flux or lumen .. these flood lights are used for outdoor lighting , road lighting etc.

High bay lights

High bay lights are used on ceilings .these lights are used in stadiums , warehouse and industry with ceiling height more than 25 feet.

Medium bay or low bay lights are also there and they are also mounted on ceilings with respect to height of ceiling.

Mounting height

Two definitions are there ..

  • Vertical distance between light fixture and work plane
  • Vertical distance between light fixture and floor

Occupancy sensor

A sensor that detects occupancy of han inside a room or space and turns on the lighting depending on occupancy of people inside room or space .

Pendant light fixture or luminarie

Pendant light fixture is the light that hangs from the ceiling by a cable or chain.

This Post Has One Comment

  1. Jaskiran Kaur

    This is a very informative articles .So, much knowledge in article these days is found less. I want to add my thoughts that every Electrician company should have an app too. An app can be so beneficial for both customers and company as the app can provide them so many features like scheduling, blogs, customer feedback, tools selling and much more .I came across a website ‘Cerebrum Infotech’ few days ago They develop Handyman apps life for Electrician, plumber, etc .

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