Total radiant flux measurement of an LED with an optometer

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SUMMARY

The forum discussion centers on measuring total radiant flux of the SFH 4550 LED from Osram using an optometer, yielding approximately 70mW. When a 5mm rubber hose is placed around the LED, the power drops to 40-50mW, raising questions about heat effects and light emission angles. The user also discusses measuring the VSMY2850RG LED, noting a power increase from 30-35mW to 55mW when placed inside an integrating sphere, highlighting inconsistencies in manufacturer specifications regarding power intensity plots.

PREREQUISITES
  • Understanding of LED characteristics, specifically half-angle emission.
  • Familiarity with optometry tools, particularly optometers.
  • Knowledge of integrating spheres and their role in light measurement.
  • Basic principles of thermal management in LED applications.
NEXT STEPS
  • Research the thermal effects on LED performance at varying currents.
  • Learn about integrating sphere calibration techniques for accurate flux measurements.
  • Explore LED emission patterns and their impact on measurement accuracy.
  • Investigate manufacturer specifications for LED intensity and power ratings.
USEFUL FOR

Engineers, optical scientists, and LED manufacturers seeking to understand the nuances of LED flux measurement and the impact of environmental factors on performance.

vst98
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Measuring the total radiant flux with an optometer of SFH 4550 LED from osram I'm getting ~70mW,
If I place 5mm long rubber hose around the led (top 2,5mm of the led is free), the power is reduced to 50-40mW.
This does not make sens to me, the led has a half angle of ±3° and emits nothing to its sides,
why is the power then reduced so much ?
 
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Is it getting a lot hotter?
 
I have a constant 100mA current going through the led, that could be a reason, but I have not noticed that.
If a place this rubber hose at the top of the led, so that most of the led housing is not covered, I am again
having significant power loss. I have also placed the led in a small aluminum tube (~10mm long same diameter as the led) and
again there is a power loss. I do not understand, this all should not make a difference if an led emits almost all of its power in ±3°.

One more thing, I have also measured total power flux of VSMY2850RG, a ±10° led. If I place the led at the
entrance of the integrating sphere I have ~30-35mW, only when I place the led completely inside the sphere
the power is ~55mW as stated in the specs. Ok, I think it's now clear to me why, the chip is encapsulated in transparent epoxy, but ...
I wonder why is vishay producing reverse versions of this thing :smile: ?
Why it is so hard for led manufacturers to state to which power the intensity plot is related ?
 

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