Total radiant flux measurement of an LED with an optometer

In summary, the speaker is discussing their experimentation with measuring the total radiant flux of the SFH 4550 LED from Osram. They have observed a decrease in power when placing a rubber hose or aluminum tube around the LED, which they find puzzling since the LED has a narrow beam angle. They also mention measuring the flux of a ±10° LED and noticing a difference in power depending on its placement within an integrating sphere. They express confusion about LED manufacturers not clearly stating the intensity plot and mention Vishay producing reverse versions of the LED.
  • #1
vst98
51
0
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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  • #2
Is it getting a lot hotter?
 
  • #3
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 ?
 

What is total radiant flux measurement?

Total radiant flux measurement is the process of quantifying the total amount of radiant energy emitted by a source, in this case an LED, in all directions.

Why is it important to measure the total radiant flux of an LED?

Measuring the total radiant flux of an LED is important because it allows us to assess the overall performance and efficiency of the LED. It also helps in comparing different LEDs and determining the most suitable one for a specific application.

What is an optometer and how does it measure total radiant flux?

An optometer is a device used to measure light intensity. It typically consists of a photodetector, which converts light energy into electrical current, and a display unit. To measure total radiant flux of an LED, the optometer is placed in front of the LED and the photodetector measures the light energy emitted in all directions.

Can total radiant flux measurement be affected by external factors?

Yes, total radiant flux measurement can be affected by external factors such as ambient temperature, humidity, and the angle at which the optometer is placed in relation to the LED. It is important to control these factors to ensure accurate measurements.

Are there any industry standards for total radiant flux measurement of LEDs?

Yes, there are industry standards such as IES LM-79 and CIE S 025/E:2015 which provide guidelines for measuring the total radiant flux of LEDs. These standards specify the equipment, procedures, and conditions for accurate measurements.

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