Photometry / radiation question

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SUMMARY

The discussion focuses on calculating luminous intensity and illuminance based on given radiant power and luminous flux values. The radiant power is 45 mW, and the luminous flux is 22 lumens, uniformly spread over a hemisphere. The luminous intensity is determined to be 11π candela (lm/sr), utilizing the relationship between luminous flux and the solid angle of a hemisphere. Additionally, the discussion addresses the calculation of illuminance at specific distances from the light source.

PREREQUISITES
  • Understanding of photometric and radiometric units, including luminous flux and radiant power.
  • Familiarity with the concept of luminous intensity and its measurement in candela.
  • Knowledge of the relationship between luminous efficacy and photometric calculations.
  • Basic principles of geometry related to solid angles, particularly hemispherical geometry.
NEXT STEPS
  • Research the formulas for calculating illuminance at various distances from a light source.
  • Learn about luminous efficacy and its role in converting radiometric to photometric units.
  • Explore the application of photometric units in real-world lighting design scenarios.
  • Investigate the differences between photometric and radiometric measurements in optical engineering.
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Students and professionals in optics, lighting design engineers, and anyone involved in photometry or radiometry seeking to understand the calculations related to luminous intensity and illuminance.

ginnerpip
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Hey guys (and girls)

I've got a rather annoying question.

If you were given the radiant power (45 mW) and luminous flux (22 l), and then was told it was spread uniformly spread over a hemisphere. (a) how do find the luminous intensity??, (b) the illuminance 1.8m away, and (c) illumance 5.0 cm straing out, and 3.0cm to the side.

The first questioj is really annoying me, any help??

Thanks
 
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ginnerpip said:
Hey guys (and girls)

What about the rest of us?
 
Phew, all those funky optical jargon units are pretty annoying sometimes.
Let's see:
Radiant energy is [itex]Q_e[/itex], so radiant power is probably [itex]\frac{dQ_e}{dt}[/itex], measured in Joules and J/s (Watts).
While luminous energy is measured in lm-s (talbot)
and the luminous flux is [itex]\frac{dQ_v}{dt}[/itex] where [itex]Q_v[/itex] is the luminous energy. The unit of flux is lm (lumen).
the Luminous Intensity (candlepower) [itex]I_v[/itex] is lm/sr (lumen per steradian) or cd (candela).

You have to have some formula for switching from photometric units to radiometric units. According to my opicts book it's:
[tex]photometric unit = K(\lambda)\times radiometric unit[/tex]
where [itex]K(\lambda)[/itex] is the luminous efficacy.

The first question is not so tough. Since the luminous flux is 22 lm and the luminous intensity is lm/sr and a hemisphere has [itex]2\pi[/itex] steradian, the luminous intensity is [itex]11\pi[/itex] lm/sr.

You really don't need the radiant power after all.
 
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