Help with an electronic circuit (Why does the LED turn on when I touch it?)

[Tigermisu]

Hello! I have the following circuit:

I'm a begginer in electronics and I coded this in python using a raspberry pi, it counts in binary to 7.

It works great, there is just some odd thing that makes me curious:

The red LED is much more brighter than the other 2 when counting, and if I happen to touch the red led when the circuit is off (Or even if I hold the positive side out of the breadboard while leaving the negative one going to the resistance and then ground) the led turns on very dimly. I replaced the red one with another and this behavior didn't occur.

Why is this?

[Shpaget]

Photo is not clear enough to see what is connected where, so I'll just give you some generic responses.

The red LED shines brighter because its forward voltage is lower than the yellow or the green ones, meaning there is more current flowing through it when using the same value resistors.

It lights up when touched because you most likely have some 50/60Hz hum in the circuit that is coming though the power supply. Mains hum is notoriously hard to get rid of, so if that's the case I wouldn't even try to do much about it. Why you can do is to try using a different power supply, preferably a battery to see if it fixes the issue.

Why it stopped glowing once you replaced it? I don't know. When you return the glowing one does it shine? If no, I'd say there is some other factor involved (you touching a grounded object like a PC case, central heating radiator...).

[Tigermisu]

The photo is not very clear, but everything is connected to the power source, then a LED, then a 220ohm resistor, then to the -3v part.

I will try and return the glowing one, see if it shines again.

[YNM]

Consider posting a better picture should help with figuring out what's wrong by guys over the .net . It just takes at least an online storage account (like, dropbox) then upload photo, share (and modify a bit) the link.

[Nuke]

the formula to determine the resistor is: resistorValue = ( supplyVoltage - ledForwardVoltage ) / ledForwardCurrent (amps, not ma, divide by 1000 to convert).

different colors have different voltage drops, different forward current ratings, and different luminous intensity. some are designed to be very bright and others less so. values can vary quite a bit from part to part.

that board looks like it has some logic level conversion mosfets on there. other side of the ribbon cable plugs into the pi's gpio header. the raspberry pi uses 3.3v logic levels, but most bread boarding is done at 5v. it kind of makes sense. if i were to take a guess why the red led comes on when touched, i would say make sure your resistor wires dont cross. also you may be acting as a pull down resistor and tripping the mosfet.