Very Low Current LED

[pancho_hideboo]

Is there any LED which can lighten in low current such as 100uA ?

 

[KlausST]

Hi,

about any LED will do.

Klaus

 

[pancho_hideboo]

about any LED will do.

No........
We can not even detect light since it is very very dark.

 

[KlausST]

Hi

Why do you say so?

Pure LEDs (without additional internal circuit) have a very good current_to_brightness linearity.
So if it is designed for 20mA, then with 100uA it will have about 1/200 of brightness. Very good visible. I just tested it at a random blue LED.

Klaus

 

[FvM]

LEDs have no threshold current. You'll look for LEDs with high mcd/mA efficiency and probably lower viewing angle.

 

[pancho_hideboo]

LEDs have no threshold current.
You'll look for LEDs with high mcd/mA efficiency

Could you teach me any good product ?

 

[KlausST]

Hi,

I just tested 4 different colourend LEDs all emit light.
The yellow (very old) ones are barely visible. (I don´t know if this is by age, by internal circuitry, by technology or by color)
But all the others are very good visible.

A simple "no" is definitely wrong.

Klaus

- - - Updated - - -

Hi,

Could you teach me any good product ?

You first have to specify "good"

Klaus

 

[pancho_hideboo]

Stanley FHR1105P-TR

Red
Size : 1.0 x 0.5 x 0.25mm ( L x W x H )
32mcd at IF=5mA

32mcd/5000uA=0.0064mcd/uA
0.64mcd/100uA

I just tested 4 different colourend LEDs all emit light.
The yellow (very old) ones are barely visible.
(I don´t know if this is by age, by internal circuitry, by technology or by color)
But all the others are very good visible.

Are they surey IF=100uA ?

 

[KlausST]

Hi,

IF= 100uA: I tested all with 10V and a series resistor of 100k. It surly is in the range of 100uA. There can´t be a huge error.

For sure leakage currents will cause uneven brightness.

but 5mA to 100uA is just a factor of 50.
I assume: the more clean the production the more pure the silicon the closer you come to the ideal brightness.

You won´t find "low current LED" with comparable brightness than your LED. It´s a problem of LED efficiency.
Or you use several LED dice in series. So 100uA combined with 100uA of current will give better brightness.

Klaus

 

[c_mitra]

If the LED is showing good brightness at 20mA, then it will be clearly visible at 100uA.

As others have pointed out, the light output vs current graphs is remarkably linear. And this is true independent of the color of the LED.

Perhaps your particular LED is not bright enough at 10-20mA? Try a different one.

 

[pancho_hideboo]

Perhaps your particular LED is not bright enough at 10-20mA?
Try a different one.

Stanley FHR1105P-TR
Red
Size : 1.0 x 0.5 x 0.25mm ( L x W x H )
32mcd at IF=5mA
32mcd/5000uA=0.0064mcd/uA
0.64mcd/100uA

Rohm SML-311UT
Red
Size : 1.6 x 0.8 x 0.8mm ( L x W x H )
2.5mcd at IF=2mA
2.5mcd/2000uA=0.00125mcd/uA
0.125mcd/100uA

Stanley's LED is a good candidate.

Is there more good LED ?

I will use LED in UHF passive RFID system.

 

[KlausST]

Hi,

Is there more good LED ?

We still don´t know waht "ggod" means for you.
The only constant informaion in your given LEDs is "red".

100uA --> if it´s not hard for me to use a 10V supply and a 100k resistor, then it shouldn´t be hard for you to do a similar test.

Klaus

 

[c_mitra]

Is there more good LED ?

Human eye is not equally sensitive to all wavelengths: see e.g., https://www.npl.co.uk/publications/...an-eye-and-light/the-eyes-response-to-colour/

A green LED appears brighter- with the same output. The candela definition is both confusing and ambiguous - see https://en.wikipedia.org/wiki/Candela

 

[pancho_hideboo]

100uA --> if it´s not hard for me to use a 10V supply and a 100k resistor,
then it shouldn´t be hard for you to do a similar test.

10Volts ?
Do you have actual experience of electric product design ?

 

[FvM]

The candela definition is both confusing and ambiguous.

candela unit is already weighted with eye sensitivity function. Different LED colors with same cd should give same intensity impression.

10Volts ?
Do you have actual experience of electric product design ?

What has a test method to do with product design?

 

[KlausST]

Hi,

10Volts ?
Do you have actual experience of electric product design ?

What do you mean? I´m doing a lot of industrial design.

10V combined with 100k just gives about 100uA. For sure with 12V one would be closer to 100uA. But to test the brightness it is sufficient. You won´t recognize the difference.

Klaus

 

[c_mitra]

candela unit is already weighted with eye sensitivity function. Different LED colors with same cd should give same intensity impression...

The current definition is: The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10^12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

And this is from the source: https://physics.nist.gov/cuu/Units/candela.html

The definition is confusing because it appears that a source that emit any other wavelength will have ZERO luminous intensity; and
I think it is ambiguous because in college we visually compared the intensity using a grease-spot photometer...
But I do not find any reference to the eye sensitivity function in the definition...

 

[FvM]

The quoted calibration specification is the link between radiometric (energy related) and photometric (eye sensitivity related) units.

Please review https://en.wikipedia.org/wiki/Photometry_(optics) for an explanation. Or a profound optics text book.

 

[c_mitra]

Is there more good LED ?

you may please check https://donklipstein.com/ledlocul.html

Plenty of interesting information...

 

[FvM]

you may please check ...

I've seen modern LEDs with even higher mcd/mA, but not in 0402 package as apparently preferred by pancho_hideboo.