Also, no LED will be blindingly bright at 2mA.

Not sure I believe that.

 

Not sure I believe that.

OK, testing with a green LED (the most subjectively bright) at 2mA it's bright but I can look at it. It's not blinding. It's probably too bright for an indicator but its not painful or even uncomfortable. With a white LED at 2mA, it's a bit less. Bright, not blinding.

But one outcome of the test is that I find the white LED draws 2mA at 2.69V so the TS's numbers are probably correct.

 

There are some high efficiency white leds that operate around 2mA instead of 20 mA. I used a white high efficiency LED to replace the stereo indicator lamp in a tuner. They were pretty rare at the time. I had to do some shenanigans (zener diodes and resistors) to get it to work with a complete OFF and a complete ON. Some photoMOS relays operate at 1 mA.

 

There are some high efficiency white leds that operate around 2mA instead of 20 mA.

Then the LED illuminates so much that I actually can't look at it.

I wasn't saying LEDs don't emit light at 2mA. In fact, I measured sub-μA current for an illuminating white LED in #16 . I was saying that LEDs don't get blindingly bright at 2mA.

That said, I see I might have misread the TS. He might mean above 2mA the LED becomes impossible to look at, which could be accurate, so if that's what he meant I can probably agree.

Also, the light level at 2mA is not low on-axis to a narrow angle LED and surely the discomfort is subjective so it might be a reasonable description of his experience at 2mA.

 

Nobody mentioned the viewing angle of an LED.
Cheap LEDs are dim ones in a case that focuses the light beam into a fairly bright but narrow angle.
Modern LEDs are very bright but with a wide viewing angle. A few modern LEDs are in a case that focuses the light beam into a blindingly super-bright narrow angle like a laser beam.

 

Nobody mentioned the viewing angle of an LED.
Cheap LEDs are dim ones in a case that focuses the light beam into a fairly bright but narrow angle.
Modern LEDs are very bright but with a wide viewing angle. A few modern LEDs are in a case that focuses the light beam into a blindingly super-bright narrow angle like a laser beam.

I mentioned it?

Also, the light level at 2mA is not low on-axis to a narrow angle LED and surely the discomfort is subjective so it might be a reasonable description of his experience at 2mA.

 

I mentioned it?

Any way, this is a total diversion from the thread.

I have to admit I don't really understand what the TS is trying to accomplish. I probably should just step back.

 

Also, no LED will be blindingly bright at 2mA.

I agree that "blinding" is exaggerated, but the highly focused ones, up close on your bench, can be pretty darn bright if your eye is on-axis with the beam.

Oops, I see I'm late with my comment.

 

I have been testing a setup with a voltage supply I had laying around and it supplies with 24.50 volt.

I put 9 white LED's in seriel with a 3,265 ohm resistor.

Then I started measuring.
I measured the forward voltage over a single LED to 2.605 volt
The forward voltage over the resistor to 1.168 volt
The total forward current measured 0.34mA (see picture)

What should I conclude of this setup? Does it really use that little power?

 

I have been testing a setup with a voltage supply I had laying around and it supplies with 24.50 volt.

I put 9 white LED's in seriel with a 3,265 ohm resistor.

Then I started measuring.
I measured the forward voltage over a single LED to 2.605 volt
The forward voltage over the resistor to 1.168 volt
The total forward current measured 0.34mA (see picture)View attachment 236929

What should I conclude of this setup? Does it really use that little power?

Those LEDs are emitting light but until you drive them to their rated current (probably 20mA) you are only measuring something incidental: when the begin to light. They have ratings for forward voltage, current, and light output which are only valid at the current rating.

 

okay I did not know that. I thought I could always count on the measurements. I mean how can the multimeter know that it measures an LED not getting the amount of current its datasheet requires.

So how can I measure its actual power consumption?

 

So how can I measure its actual power consumption?

Voltage times current.
Off topic but this reminds me of a circuit I posted many years ago where I used a white LED and describing it as "easily visible at 1ma". Well this guy replied and remarked that my circuit was irresponsible because I wasn't operating the LED at 20ma.
I replied and said there was no law that you have to operate a LED always at 20ma. His reply was "yes there is, it's called Ohms Law". At that point I threw my hands up and walked away.

 

I measured the current but apparently that measurement wasn't valid and I don't get why.
Is something wrong with my multimeter? because my multimeter doesn't not know what it says in the datasheet of my LEDs's. My guess was that the multimeter measures how much power is running through it no matter what I hook it up with? dont get it.

 

Voltage times current.
Off topic but this reminds me of a circuit I posted many years ago where I used a white LED and describing it as "easily visible at 1ma". Well this guy replied and remarked that my circuit was irresponsible because I wasn't operating the LED at 20ma.
I replied and said there was no law that you have to operate a LED always at 20ma. His reply was "yes there is, it's called Ohms Law". At that point I threw my hands up and walked away.

i forgot that I was going to leave this thread. I have no idea what the TS is trying to do so I should just ignore this.

 

Voltage times current.
Off topic but this reminds me of a circuit I posted many years ago where I used a white LED and describing it as "easily visible at 1ma". Well this guy replied and remarked that my circuit was irresponsible because I wasn't operating the LED at 20ma.
I replied and said there was no law that you have to operate a LED always at 20ma. His reply was "yes there is, it's called Ohms Law". At that point I threw my hands up and walked away.

The voltage is 2.6 volt and the current is measured to 0.34 mA.
2.6 x 0.34 = 0.884 watt for at single LED.

 

Incorrect. 2.6 volts x .00034 amps.

 

oh yeah sorry. missed some zeros

2.6 volt x 0.00034 A = 0,000884 watt

 

But that I can not trust? is that correct?

 

884 microwatts is correct if your meter is accurate

 

i forgot that I was going to leave this thread.

Are you still passing back and forth in an alternate reality?