LED info

[Macrosill]

Some of the webpages I visit often and have found to be very informative and helpful in learning about leds.

http://www.theledlight.com/ledcircuits.html

http://filebox.vt.edu/users/jemerick/LED_Hook_Up_Guide.pdf

[Zane]

I got to this site for leds and other pieces very easy to understand and they give you some test circuits to try out

http://www.kpsec.freeuk.com/components/led.htm

[kamahilights]

http://www.theledlight.com/ledcircuits.html

http://filebox.vt.edu/users/jemerick/LED_Hook_Up_Guide.pdf

The second reference is just fine, but the first one is so wrong I have in the past contacted them and told them so!

Statements like "Current is hardly ever mentioned" and "If three LEDs were in series with a 12V source, each would receive 4V" and "You want them to have the full 3V going to each" with the picture of leds wired in parallel with ONE limiting resistor is just much misinformation!

LED's are diodes that just happen to emit light (Light Emitting DIODE) and are CURRENT driven devices. That is, drive a current thru them and they produce a voltage drop in the forward direction called Vf, which alters depending on the color of the led. Just like a power diode, which is their cousin, they can ONLY withstand so much voltage in reverse before they "breakdown" and go usually short circuit. That is why it is important to provide them with DC, and also explains why some LED strings without rectification are having such a short life.

A normal lamp is more a voltage driven device - you apply volts to it and its internal resistance will glow and hence give off light. Double the volts applied to a normal incandensant lamp and it will blow within seconds!

There are 3 "rules" I preach for using leds, and they are:

1) Feed them with DC - this can be rectified AC, preferably with a bit of smoothing to reduce flicker but DONT rely on the LEDs to do the rectification (LED STRING MAKERS _ LISTEN UP!!!!!)

2) Always (at least) use a resistor to reduce current flow and drop at least 20% of the available voltage across this resistor. It is okay to feed leds in series (as long as this rule is not broken) but each string must have its own dropping resistor.

3) Keep the max current flow at max expected voltage within the makers max current - usually 20ma. There is not much difference in brightness between a led passing 15ma and one passing 20ma - except that power consumed by led goes from 0.048w to 0.064w! That is heat. And heat is electronics enemy!

If you fail to follow these 3 rules, you will end up with a lot shorter lifetime for your leds. You CAN abuse leds by using them to block AC, passing 30ma thru them, etc like lots of led user makers do, but you will shorten the life - leds will go dark, stop working, etc. You see, if you abuse a normal lamp in a similar way they would blow within 10 seconds . . . . the leds long life in relation to a normal lamp allows it to take abuse for say 10 hours . . .