Calculating distance between lux meter and light source

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SUMMARY

This discussion focuses on calculating the distance between a light source and a lux meter using the inverse square law (ISL), expressed as lux = lm/d². Participants confirm that while ISL is generally applicable, its accuracy diminishes under certain conditions, such as when the light source has a significant area or when using lasers. Experimental data is encouraged to determine the effective distance at which ISL remains valid.

PREREQUISITES
  • Understanding of the inverse square law (ISL) in photometry
  • Familiarity with lux meters and their measurement capabilities
  • Knowledge of luminosity flux and its relevance to light sources
  • Basic principles of light behavior, particularly with distributed sources
NEXT STEPS
  • Conduct experiments to measure lux values at varying distances from a light source
  • Research the limitations of the inverse square law in practical applications
  • Explore the effects of light source area on lux measurements
  • Investigate the behavior of laser light in relation to distance and measurement accuracy
USEFUL FOR

Researchers, physicists, and engineers involved in photometry, lighting design, or optical measurements will benefit from this discussion.

san-yas
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I am currently performing some experiments to calculate the distance between a light source and a lux meter where the light source points directly towards the lux meter.
Is it possible to calculate the exact distance between the light source and the lux meter given that we have a lux value (through the lux meter) and the luminosity flux (through the information given by the light source manufacturer)? or is the inverse square law (lux=lm/d^2) subjected to particular conditions?
 
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Welcome to PF.

It seems like the inverse square law should work for this. What have you seen in your experimental data so far?
 
san-yas said:
a light source
If the source has a significant area then ISL will stop working close up. Also, if the source is a laser, you will have a problem because the effective position of the source can be may metres behind the front (multiple mirror images, as with an infinity mirror) and the r in 1/r2 would need to be corrected for. ISL is fine for stars and planets but the Moon and Sun are very much distributed sources.

I would be inclined to do the experiment first and find what distance the ISL begins to work for.
 
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