LED currents?

[Jan Panteltje]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.
I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

 

[Jamie]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.
I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

how about PWM it?


--
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"Daily Thought:

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"

 

[Winfield]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.
I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

Use a wide-viewing-angle diffused-lens LED,
for an overall pleasant useful appearance.

 

[[email protected]]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.
I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

Yeah LEDs are very efficient these days, almost blinded myself with a
stupid SMT red LED on one of my projects.
It was just supposed to be a power LED, not an optical warfare
component...

 

[DJ Delorie]

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

For "blinky light" indicators, I use 1k per volt Vcc. So, 3.3k for
3.3v, 4.7k for 5v, 12k for 12v, etc.

That's less than 1mA current (due to the Vf drop), but it's enough to
easily tell that the LED is on without casting that warm glow
throughout the room.

Example: for the average green LED (2.0V Vf) at 3.3v: (3.3 - 2.0) =
1.3v across the resistor, 1.3v / 3300R = 0.4mA

5v -> 0.6mA

There is quite a range of "lumens" for LEDs, I like to buy the
brighter ones because I can drive them directly from GPIO ports
without the extra transistor.

 

[Don Klipstein]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.
I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

If the green LED is one of those InGaAlP ones, half a milliamp is
probably about right for "normal LED indicator lamp" brightness. At that
current, voltage drop is about 2.9 volts, so the dropping resistor would
be about 3.9K or 4.7K or so.

I have had some better ones work just fine at .3 milliamp.

InGaAlP green LEDs tend to have nominal wavelengths around 520-530 nm.
Their color varies a little with current, and at half a milliamp expect a
pretty lime green or greenish lime green color.

- Don Klipstein ([email protected])

 

[Joerg]

For "blinky light" indicators, I use 1k per volt Vcc. So, 3.3k for
3.3v, 4.7k for 5v, 12k for 12v, etc.

That's less than 1mA current (due to the Vf drop), but it's enough to
easily tell that the LED is on without casting that warm glow
throughout the room.

Example: for the average green LED (2.0V Vf) at 3.3v: (3.3 - 2.0) =
1.3v across the resistor, 1.3v / 3300R = 0.4mA

5v -> 0.6mA

There is quite a range of "lumens" for LEDs, I like to buy the
brighter ones because I can drive them directly from GPIO ports
without the extra transistor.

Does anyone know what those super-bright LEDs in the Harborfreight head
lamp can stomach over the long haul? There is no part number on them.

 

[Tim Williams]

Does anyone know what those super-bright LEDs in the Harborfreight head
lamp can stomach over the long haul? There is no part number on them.

Gosh, I don't think I've *ever* seen an LED (singles, not a special type)
with a part number on it.

And those that do have numbers are hard (impossible?) to find references
to, last I tried.

Tim

 

[Henry Kiefer]

Does anyone know what those super-bright LEDs in the Harborfreight head
lamp can stomach over the long haul? There is no part number on them.

Just test it. But I would wonder if they last longer than 100 hours.

- Henry

 

[Don Klipstein]

Does anyone know what those super-bright LEDs in the Harborfreight head
lamp can stomach over the long haul? There is no part number on them.

Most "regular size" white LEDs are characterized at 20 mA, and I hear a
few life figures of 6,000 and 10,000 hours, though sometimes 50,000 hours
for some.

I have seen some with a halflife appearing to me about 4,000 hours at 30
mA.

If you don't mind faster aging, my experience is that most don't mind 40
mA too much and you have a fair chance of getting away with 50, especially
with some heatsinking on the negative leads (such as large copper areas in
a circuit board).

Keep in mind that the usual white LEDs are nonlinear, with maximum
efficiency when moderately underpowered (maybe 5 mA or so for "regular
size" / "low power" ones).

- Don Klipstein ([email protected])

 

[Jan Panteltje]

how about PWM it?

Yes that would work, but I need timers for other things too...
And that would add a user control.
Not a bad idea... maybe add a photo cell and measure room light....
But it defeats simplicity

 

[Jan Panteltje]

Use a wide-viewing-angle diffused-lens LED,
for an overall pleasant useful appearance.

Thank you Winfield, I will have a go at some catalogs.

 

[Jan Panteltje]

Yeah LEDs are very efficient these days, almost blinded myself with a
stupid SMT red LED on one of my projects.
It was just supposed to be a power LED, not an optical warfare
component...

LOL

 

[Jan Panteltje]

For "blinky light" indicators, I use 1k per volt Vcc. So, 3.3k for
3.3v, 4.7k for 5v, 12k for 12v, etc.

That's less than 1mA current (due to the Vf drop), but it's enough to
easily tell that the LED is on without casting that warm glow
throughout the room.

Example: for the average green LED (2.0V Vf) at 3.3v: (3.3 - 2.0) =
1.3v across the resistor, 1.3v / 3300R = 0.4mA

5v -> 0.6mA

There is quite a range of "lumens" for LEDs, I like to buy the
brighter ones because I can drive them directly from GPIO ports
without the extra transistor.

Yes, looks like I will have to go to lower currents too.

 

[Jan Panteltje]

If the green LED is one of those InGaAlP ones, half a milliamp is
probably about right for "normal LED indicator lamp" brightness. At that
current, voltage drop is about 2.9 volts, so the dropping resistor would
be about 3.9K or 4.7K or so.

I have had some better ones work just fine at .3 milliamp.

InGaAlP green LEDs tend to have nominal wavelengths around 520-530 nm.
Their color varies a little with current, and at half a milliamp expect a
pretty lime green or greenish lime green color.

- Don Klipstein ([email protected])

Thank you Don, that confirms also what DJ Delory suggests I use.
Yes I think these LEDs are those InGaAlP, they are a different green then some older
ones I have, I will play with the current a bit to see if the color changes.

 

[Eeyore]

I was just soldering a LED in a PIC circuit so I can test
some software I am writing.
Now I want low brightness, so I derated, 680 Ohm in series, 5V,
3 V LED drop, green LED.

Since WHEN did green LEDs have a Vf of 3V @ a couple of mA ? It'll be
more like 1.6V.

So I = 3.4/680 = 5mA

I bought some of the brightest greens ones some time ago...
Switched it on, had to close my eyes: 2.9 mA WAY to bright!!!

If you bought an ultra-bright one no surprise. Also watch out for the
view angle.

So what do you guys use for LED current these days for a normal
non blinding clear transparent green LED (say on indicator)? < 1mA?

Often about 3mA with a run-of-the-mill LED and 10mA if I want it to be
bright.

Graham

 

[Joerg]

Just test it. But I would wonder if they last longer than 100 hours.

Well, that's why I was asking since they might drive them a bit past
their usual limits

 

[Joerg]

Most "regular size" white LEDs are characterized at 20 mA, and I hear a
few life figures of 6,000 and 10,000 hours, though sometimes 50,000 hours
for some.

I have seen some with a halflife appearing to me about 4,000 hours at 30
mA.

If you don't mind faster aging, my experience is that most don't mind 40
mA too much and you have a fair chance of getting away with 50, especially
with some heatsinking on the negative leads (such as large copper areas in
a circuit board).

Keep in mind that the usual white LEDs are nonlinear, with maximum
efficiency when moderately underpowered (maybe 5 mA or so for "regular
size" / "low power" ones).

- Don Klipstein ([email protected])

Thanks, Don, that's good information. So I'll keep them to 20mA then.

 

[Spehro Pefhany]

Does anyone know what those super-bright LEDs in the Harborfreight head
lamp can stomach over the long haul? There is no part number on them.

In the long run they will ALL go dead.


Best regards,
Spehro Pefhany

 

[Joerg]

In the long run they will ALL go dead.

Why is that? Sloppy processes or something like that?