How to analyse the luminous intensity at various distances from the light source

- February 17, 2025 at 8:33 am
  S.Manuvarshan
  Subscriber
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Hello,

In Ansys SPEOS 2024 R1,

I created two intensity sensors (same origin axis) at differenent distances from the source.

One is located at a distance of 480 mm and the other is located at 1000 mm.

I checked the intensity values after the simulation. Both of them showed the same intensity in candelas (cross checked with various measurement positions).

But, according to the inverse square law, the luminous intensity must fall with greater distances right (intensity ∝ 1/d2) ?

Why i did not see any change in intensity ? suppose if i had done a wrong sensor construction in SPEOS, kindly correct me.

Thanks & Regards
Manu Varshan
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- February 18, 2025 at 2:44 pm
  
  nomad
  Subscriber
  
  You can check this userguide, Understanding the Parameters of an Intensity Sensor.
  Also you can contact Ansys local support and ask more specific questions from https://customer.ansys.com
- February 27, 2025 at 7:32 am
  Karabasappa Tallur
  Ansys Employee
  Hello,
  
  Please find the explanation for your query below
  Luminous Intensity (Candela - cd):
  Luminous intensity is the amount of light power emitted by a source in a specific direction, measured in candelas (cd). It represents how bright a source appears when viewed from a particular angle.
  Mathematically:
  $I=Φ/Ω$
  where:
  - $I$ = Luminous Intensity (cd)
  - $Φ$ = Luminous Flux (lumens, lm)
  - $Ω$ = Solid Angle (steradians, sr)
  Key Points:
  1. It describes the directional brightness of a source.
  2. It does not change with distance (unlike illuminance).
  3. A point source emitting uniformly in all directions has a total intensity distributed over a 4π steradian solid angle.
  Luminous Intensity (cd) vs. Illuminance (lux)
  - The inverse square law applies to illuminance (lux), which measures how much light falls on a surface.
  - Luminous intensity (cd), however, describes the amount of light emitted in a specific direction. If the light source is directional, the intensity may remain constant across different distances.
    
    Thanks
- February 27, 2025 at 8:26 am
  
  Alessia Fra
  Ansys Employee
  
  Hello,
  the visualisation radius just affects the graphics, but the intensity sensor still have an infinite radius.
  If you want to calculate the intensity at a specific distances, you need to switch to TRUE the parameter NEAR FIELD that you have inside the sensor's definition window: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v2511/en/Optis_UG_ASP/Optis/UG_ASP/understanding_the_parameters_of_an_intensity_sensor_180916.html
  Thanks and kind regards
- February 28, 2025 at 9:39 am
  S.Manuvarshan
  Subscriber
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Hello Alessia,

It's very similar to the case of lightweight & heavyweight geometries!

Thank you very much for clarifying.

Have a nice day!

Best Regards
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