How to Calculate Light Emitted from an LED Screen

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Discussion Overview

The discussion centers on calculating the light emitted from an LED screen rated at 5000 nits, specifically how to determine the total light output, as well as the light intensity on the floor at distances of 1 meter and 10 meters from the screen. The scope includes practical applications of photometry and radiometry, with a focus on rough calculations rather than detailed analysis.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks assistance in calculating the light emitted from a 64 sqm LED display rated at 5000 nits, specifically in LUX.
  • Another participant clarifies the difference between nits and lux, stating that nits is a unit of radiance while lux is a unit of irradiance, and suggests using the fundamental equation of radiative transfer for calculations.
  • A participant questions whether they can ignore the directional radiance (L(Ω)) if the screen and the projected surface are parallel, and proposes a conversion of 5000 nits * π = 15700 lux, expressing uncertainty about the steradian and the implications of distance on calculations.
  • Further discussion emphasizes the importance of energy transfer and suggests specific equations from a referenced book to guide the calculations.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the calculations and the implications of distance and geometry on the light intensity. There is no consensus on the correct approach or final values, as multiple viewpoints and methods are presented.

Contextual Notes

Limitations include the assumptions about the geometry of the LED screen and the projected surface, as well as the potential complexity introduced by the screen being a planar light source. The discussion does not resolve these complexities.

pixelpusher
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Hi,

I have a question how to calculate the light emitted from a LED screen. The LED display is rated at 5000 nits. Total size of the display is 64sqm. (8m x 8m touching the floor) I would like to calculate the total light emitted, the light on the floor in front 1m away and the light on the floor 10m away. The calculations don't need to factor in every detailed aspect, I am looking for a rough value how the screen would affect the lighting situation in it's vicinity at full white.

Light on the floor should be calculated in LUX, correct? Can somebody help me out with the calculation? Much appreciated, light calculations are quite confusing at times. Thanks
pp
 
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Yikes...

"Nits" is a photometric unit of radiance, and 'lux' is a photometric unit of irradiance. So at least the conversion is straightforward. What you need to know is the L(Ω), how the radiance varies with direction. Maybe the LED is lambertian (L is constant), maybe not. Either way, it's pretty much geometry- you have an emitting plane and a receiving plane oriented at some angle to the emitter, so use the 'fundamental equation of radiative transfer' to calculate whatever you need:

https://books.google.com/books?id=i...tion of radiative transfer radiometry&f=false
 
Thanks for your answer Andy. So if the screen and the projected surface would be parallel to each other I could ignore L(Ω)? Would 5000 nits * π = 15700 lux be sufficient as conversion? Not sure about the steradian? Why only 1*π ? What about increasing distance? Is it impossible to calculate, because the screen is a planar light source? My head hurts..

Thanks
 
pixelpusher said:
Thanks for your answer Andy. So if the screen and the projected surface would be parallel to each other I could ignore L(Ω)? Would 5000 nits * π = 15700 lux be sufficient as conversion? Not sure about the steradian? Why only 1*π ? What about increasing distance? Is it impossible to calculate, because the screen is a planar light source? My head hurts..

Yeah, radiometry/photometry can be like that. Just remember that it's all about the transfer of energy. You are right to start with the surfaces facing each other, that simplifies things considerably. Begin by working through eqns 3-9 to 3-4 in the reference I provided above. Then section 3-3 can guide you through your problem, eqn 3-20 is particularly relevant, as are eqns 3-24 through 3-28.

Wolfe's book is excellent and worth having around for reference.
 

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