basic (stupid) LED current question

Hi,

I got this (1000pcs) yellow 5mm led ...
**broken link removed**

but, I cannot decipher:

Vf: 1.80V typ, Iv: 50-100mcd

Vf: 1.8V is forwarding voltage drop - clear

but ... Iv 50-100mcd ?!?!?! wth ??? 50mA - 100mA ? this leds does not look they can survive 100mA and already over 20mA they get bit orange (still cold but not as yellow as at 15mA, little bit more orange) ...

I had bad luck some years back trying out the max led current as one blow up into small pieces and a piece was stuck into mine hand so I'm not keen on trying it out again

Depends on what you want to do with them (do you want them as bright as possible?). I would run them at about 20-30ma. To save power on my circuits I even run some LED's <5ma.

Boomslang said:

Depends on what you want to do with them (do you want them as bright as possible?). I would run them at about 20-30ma. To save power on my circuits I even run some LED's <5ma.

Click to expand...

just did the test .. with 1K pot and 9V supply

optimal brightness 8-15mA (almost no difference between 8 and 15mA) from 15-25 is very bright and does not emit any heat, 25-35mA I'm not sure, it is bit brighter and I believe (but not 100% sure) it emits some heat. Somewhere after 35 (I think around 45mA) it got orange and died (no explosion nor smoke this time )

I decided to run them at 10mA (I will be using them as backlight for AV meter lcd I will embed in PSU I'm making)

The question on "wth" the Iv: 50-100mcd means ... probably something like 50-100mcd of "brightness" emitted when current is in range 5-30mA but I'm not sure

arhi said:

just did the test .. with 1K pot and 9V supply

optimal brightness 8-15mA (almost no difference between 8 and 15mA) from 15-25 is very bright and does not emit any heat, 25-35mA I'm not sure, it is bit brighter and I believe (but not 100% sure) it emits some heat. Somewhere after 35 (I think around 45mA) it got orange and died (no explosion nor smoke this time )

I decided to run them at 10mA (I will be using them as backlight for AV meter lcd I will embed in PSU I'm making)

The question on "wth" the Iv: 50-100mcd means ... probably something like 50-100mcd of "brightness" emitted when current is in range 5-30mA but I'm not sure

Click to expand...

hi arhi,
It means milli Candela. a unit of light intensity,, look up Candela.

https://en.wikipedia.org/wiki/Candela

arhi said:

Iv 50-100mcd ?!?!?! wth ??? 50mA - 100mA ? this leds does not look they can survive 100mA and already over 20mA they get bit orange (still cold but not as yellow as at 15mA, little bit more orange) ...

Click to expand...

Iv 50-100mcd is the maximum led brightness specification, which may be anywhere between those two values.

For cheap general purpose indicator leds such as those, they are probably only intended for use at a low current such as 10mA.

eric, picasm, I know what mili candela is ... but ... the thing that confuses me (yup I feel extremely stuped asking this ) is how the heck is Iv related to value in mcd ?!?!

darn ... I hate my country ... ... In school I learned that Luminous intensity symbol is L and now I see that it is Iv in SI .... stupid physics professor ...

all clear now ... I mixed up If and Iv (forward current and lum intensity) so I expected Iv to be in mA and not mcd idiot

thanks all

The Chinese spec's leave you guessing about the range of forward voltage and even the typical forward voltage at a certain (not mentioned) current.
The same for the luminous intensity (Iv or brightness) where they don't say at what current.
They don'r say what is the max allowed current.

I guess they don't want you to know that most of their cheap LEDs fail at 20mA when good ones last forever.

I won't buy cheap no-name Chinese parts that don't have a detailed datasheet.

@audioguru, yes I agree about the cheap not documented parts and relation of quality vs price .. but as I had need for bunch of "indicators" where 10mA is more then enough I got 3000 led's (red, green a yellow) of those cheap ones... even if 50% of them is already dead with other 50% working fine @ 10mA I got a good deal (10$ for 1000pcs) comparing to prices I have locally...

The lack of data *is* something I hate ... but the biggest confusion here was that I read "Iv" as current and not as brightness due to "high school professor that used the wrong symbol for brightness" or maybe (as that was actually 15+ years ago) me remembering it wrong ... as "default" If max for yellow led is 30mA - these ones work on 35mA (tested one over 12 hours - last night and it worked ok, no heat emitted) .. so they kinda fall into "standard".... They would probably die if run for a long time on 20mA but I assume they will last forever on 10mA - which is perfectly ok for what they are to be used for (simple internal signaling / status indicators) and if I compare price - 1000pcs - 10$ with local price ~70-140$ for the same thing I believe you get where the idea came from

btw, the "other" led's I got from them are quite "good" and documented (the tricolor, dualcolor, white and blue ones), the price is not that lower (2-3 times instead of 7-14 times) then locally so I'm pretty satisfied