Green LED I-V Curve

I'm sure I've seen some standard that specifies that red should be reserved for errors and warnings

You can find red LED clocks all over the place. I think that standard applies only to indicators intended to indicate status, not time keeping numeric LEDs.

is a current at zero or even negative voltages? So a diode will pump out very low levels of power? Perhaps the level of power is below the uncertai nty principle level of detection like the quantum foam?

The diode equation has an exponential part, and a very small constant part ; the saturation current (usually IS in a SPICE model) is the reverse current one expects at negative bias, but it's in the 1E-16 amp range, so the package and prin ted wiring leakage are usually more important.

maybe that is just a side effect of red being first led color and thus most commonly available?

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served for errors and warnings

applies only to indicators intended to indicate status, not time keeping nu meric LEDs.

st commonly available?

Not sure what that means, "most commonly available". They make them in man y colors, so obviously there's no shortage. I think they sell what people buy and mostly people buy on very frivolous matters when all else is equal. I bought a used alarm clock once because I couldn't find a decent blue on e in the stores. lol $10 shipped. It was actually for a girlfriend to go next to her TV, but she moved and I ended up with it.

I would say most people just prefer the red in LED clocks.

I have no recorded data about the photoelectric effect but, speaking from memory of a half-hearted test I once did, I can assure you that it will not be hundreds of uA. I doubt that it will even be in the "low uA" region under those conditions.

Here is my brightness cheat-sheet.

I love the Osram orange. It's a beautiful pure color.

LEDs have come a long way since the early days. I remember when it was customary to drive a red power indicator LED with 10 mA or higher. Now I often use 1mA or less with ordinary >1-cent LEDs.

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tic case. Blue LEDs behind white are very attractive I think. I much pref er blue LEDs to red ones.

reserved for errors and warnings

d applies only to indicators intended to indicate status, not time keeping numeric LEDs.

most commonly available?

any colors, so obviously there's no shortage.

sure, now you can get anything you want, I thought it was obvious that I meant historically LEDs started out a red and maybe that just stuck as the color used out of old habit

matters when all else is equal. I bought a used alarm clock once because I couldn't find a decent blue one in the stores. lol $10 shipped. It was actually for a girlfriend to go next to her TV, but she moved and I ended up with it.

blue light is probably a bad choice for an alarm clock, blue light affects melatonin production and allegedly mess with up you sleep

he light sensitivity. At the voltages I need to measure (up to 1.7 volts) the dark current would seem to be very minimal.

is a current at zero or even negative voltages? So a diode will pump out very low levels of power? Perhaps the level of power is below the uncertai nty principle level of detection like the quantum foam?

The current a low levels - roughly within 26mV of zero - looks resistive.

At negative voltages it is insensitive to voltage - the charge carriers ap pearing get swept out until you get to a high enough voltage to sustain ava lanche multiplication.

Letting light shine on an LED does generate charge carriers in the junctio n - they aren't great photo-diodes, but they can be used that way.

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the light sensitivity. At the voltages I need to measure (up to 1.7 volts ) the dark current would seem to be very minimal.

re is a current at zero or even negative voltages? So a diode will pump ou t very low levels of power? Perhaps the level of power is below the uncert ainty principle level of detection like the quantum foam?

appearing get swept out until you get to a high enough voltage to sustain a valanche multiplication.

ion - they aren't great photo-diodes, but they can be used that way.

I'm in denial about the Shockley equation. I think it's turtles all the wa y down.

e ADC of an MCU. However, I can't find a good chart of the I-V curve below 1 mA. The circuit supplies up to 1.15 mA which is measured by dropping it across a 1.5 k resistor yielding up to around 1.7 volts. This seems like it might be getting into a range where the LED might be stealing a signific ant portion of the current being measured. But none of the references I ca n find provide enough detail to know for sure. Most seem to be something a long the lines of an "artist's concept" of a curve lying along the X axis u ntil reaching some voltage where it takes off like a hockey stick. Others just seem to be a wag with only a very few points measured. None of them s how any detail at the low end with 10 mA as the lowest line on the Y axis.

LED will see, but I can't lower it too much or lose resolution of the measu rement.

I was trying to keep a part off the BOM if possible. There's already a g reen LED in use.

urrent over the voltage range of interest. But if I am using this to save adding a Zener diode but I have to have the part painted... doesn't seem w orth the trouble. The case only has small air openings, but it has a large port on top covered by plexi so the workings can be monitored. So it will have indirect light inside the case falling on the LED. The case is stain less steel, so lots of reflection.

a problem. 100's of uA will. Sounds like I should use the Zener.

I measured it for one led long ago. My memory is that sticking two led's face to face and driving one you can get about 1 part per thousand of the driving current. (maybe 1/10 that?) (part of that measurement depends on the LED efficiency.)

I don't know what happens when you forward bias it and then shine light on it. Maybe nothing?

George H.

There is actually a tape sold for that purpose. Probably just opaque electrical tape. Capitalism!

I was taking a walk the other night about 3AM and kept seeing brief flashes, which made sense near the lighthouse but not so much in the middle of a park. Turned out my Sony wireless headphones do that. Dunh.

Best regards, Spehro Pefhany

The original SiC Crees had a really nice light blue color too. I still have one or two samples. They looked unique, like the 1970s or older era deep red LEDs.

I believe this was an ECMA standard, or one pushed by them real hard. I'm not a fan of designed by committee european standards, but this is one that makes sense. However since europe in general seemed unable to design or build computers this issues of red lights indicating hard disk activity and not meaning a stream of errors blew over without weird fines on the importation of these computers and peripherals from Taiwan and the US.

In the old desktop PC era, green was a power indicator, yellow might be "turbo" and red was usually a HDD activity light, but this could vary, even for larger disks that had the activity light embedded in the front bezel. For network and telecom peripherals, well, red LEDs were cheap so that's what all the old gear used. I don't think I've ever seen a red LED used or an ethernet port, even for collisions on 10base-2 networks. Those were always green or yellow. Then everything went blue.

On modern servers the colors tamed a bit where red (really orange due to colorblindness concerns) means error, in line with original ECMA fantasy. It just took decades.

There are some weird side effects though, and failed hard disk can instead of lighting up red/orange indicating replacement is needed can be end up purple, which is not a documented color for disk status.

I was reading something the other day about the blue LEDs being harmful to humans.

The blue light they emit tells you that it around midday. Look at it late at night and you won't get to sleep as easily as you might.

It's not all that damaging.

they are if you throw them hard enough.

NT

I think it's all blue light, not just LEDs. When it activates the blue cones in the retina the chemical reaction creates some sort of toxin.