What is Fixture’s Beam Angle & Beam Diameter (Part-1)



  • Lamps are available with multiple beam angle options hence Beam angle is an important factor in lighting design.
  • The beam angle is the width of light that is emanated from the bulb and it is measured in degrees and can vary according to the different styles of bulbs.
  • The beam angle of the Light is mainly depend ceiling height or distance of an object from the light source, and the lux level (brightness) which is required for a particular object or floor area.

Light Terminology

  • Lumens:

  • Lumen is the total amount of light emitted by that lamp in all directions.
  • The luminous flux (Lumen) is provided by lamp manufacturers and common lumen values are included on the lamp.


  • Lux:

  • It is amount of illumination intensity in specified direction of specified area.
  • Lumen is related to lux. one lux is one lumen per square meter.
  • 1 lux = 1 lumen/m² 
  • Lux is simply the amount of lumens in a specified area.


  • Lux is measured on a distance of 1 or 10 meters.

Difference between Lumen and Lux:

  • The difference between the lumen and lux is that the lux takes into account the area over which the luminous flux (Lumen) is spread.
  • A flux of 1000 lumens, concentrated into an area of 1 square meter lights with a luminance of 1000 lux.
  • The same 1000 lumens, spread out over 10 square meters, produces a dimmer illuminance of only 100 lux.
  • Mathematically, 1 lux = 1 lm/m2.
  • Lumens are measured in all directions from the light source. This is not the best measurement to describe how bright a light is going to be on a specific area.
  • To perfect describe How much lights going to on Specified area ,luminance lux or foot-candle are used.
  • Lux changes according to beam angle and height

Difference between Beam Angle, Field Angle and Cut off Angle:

Beam Angle:

  • The beam angle is the degree of widththat light emits from a light source.
  • Beam Angle is the angle of the light between two points of 50% of Maximum intensity.
  • It helpful in knowing how much “usable” light the fixture puts out in a fairly even field.

Field angle:

  • It is the angle between the two directions opposed to each other over the beam axis for which the luminous intensity is 10% that of the maximum luminous intensity.
  • In certain fields of applications the field angle was formerly called beam angle.
  • This angle tells you how far the light reaches until it (basically) fades into the darkness.

Cut off Angle:

  • This the angle which encompasses all forward light emitted by the directional lamp.


Relation between Beam Angle and Filed Angle:

  • The Beam and Field Angles determine how a spot light lights the surrounding area.
  • Normally, the field angle should be 180 degrees, because that creates a softer transition at the edge of the beam angle.
  • If we change the default field angle to 180 to 75 this should give better results and it tighter angle, then over rider it.


Selecting Beam Angle for various Applications:

  • Beam angle is an important factor in lighting design and Lamps are often available with multiple beam angle options.
  • The beam angle of the Light we choose is determined initially by the ceiling height or distance of an object from the light source, and the lux level (brightness) that is required for a particular object or floor area.


  • Smaller beam angles (25° to 45° degrees):

  • It will produce a more focused beam of higher intensity and are more suited to spot lighting in commercial or artistic applications.
  • Buildings with very high ceilings of 3m or greater may also benefit from more focused beam angles.
  • Medium beam angle (40 degrees):

  • This is a medium spread beam that offers a good combination of intensity and coverage.
  • Wider beam angles (60 degrees):

  • Very popular for Down lights. A 60 degree beam can be used more effectively in larger rooms. Although the wider beam spread doesn’t provide more light, it does spread the light out further. If we need higher brightness, higher lumen output down lights will be required as a down lights for a good level of uniformity.
  • Larger beam angles (60° to 135° degrees):

  • It will produce a broader beam suited for most residential applications or ambient lighting in commercial applications.
  • They are also useful in lower ceiling applications (< 3m). Whereas a 45° beam spread may be more useful in higher ceiling applications or for corridor lighting.
  • A bulb with a wide beam angle ensures to get a really clear, even light.
  • The spread of light makes no dark areas in the room; and can allow you to use fewer bulbs.
  • Very Larger beam angles (120° degrees):

  • LED light bulbs of 120° or greater are used in high light dispersion applications in place of traditional incandescent or CFL light bulbs or T5, T8 and T12 fluorescent tubes. While 60° to 90° LED light bulbs are more common halogen down light replacements.


Various Beam Angle as per Applications

 (MR Type) Flood Light(PAR Type)  Spot LightDescriptionsApplications
<7°<15°Very Narrow SpotHighlight a small statue or figure on display in a museum or in a jewelry store to make diamonds “pop.”
5° to 15°15° to 30°Narrow spotSpecial or sale item or in landscape bullets illuminating a sign or garden feature.
16° to 22°30° to 60°spotUsed in stores to highlight a special or sale area or outdoors to illuminate an architectural feature.
23° to 32°60° to 90°Narrow floodhighlight a display table, while homes might use this bulb in recessed eyeball lights to illuminate a painting
32° to 45°90° to 120°floodPendant lights in coffee shops to recessed lights in living rooms.
45° to 60°120° to 160°Wide floodCommon in many general illumination applications from motion-sensing lights above garage doors to recessed cans in auditoriums and movie theaters.
>60°>160°Very wide floodused to illuminate without highlighting any particular object or area. They’re good options for outdoor flood lighting and low-ceiling recessed lights.


Ceiling Height and Beam angle

Ceiling HeightBeam Angle
2.5 to 3.5 meters60° beam angle
3.5 to 4.5 meters38° or 40° beam angle
5 meters24° to 30° beam angle