volt or 12 volt LED
Assuming we are using a LED which does NOT
require the current limit resistor (one of the 5
volt or 12 volt versions) the other leg can be
connected to a + POSITIVE voltage source, not
exceeding that required by the LED, when the LED
will light as there is a "built in " limit resistor.
However connecting such an LED round the wrong way
is likely to lead to failure as they do not like
what is called a reverse voltage.
A standard LED requires a limit resistor.
Without having to go into the maths you can assume
that a 1000 ohm resistor (1K) will be ok for most
voltage up to a maximum or 22 volts and not less
than 12 volts. On 22 volts a 1k resistor gives you a
current flowing of 22mA or for a 12 volt supply
As a generalization 22mA is considered a
maximum that the LED likes but you can go into
things more technically and look up the data sheet
for the LED in question.
There is a minimum voltage required else
the LED will not light which is about 3 volts.
The current limit resistor can be fitted in
series with either lead of the LED which should then
be insulate with sleeving to prevent a short circuit
The flashing Led has not only a built in
resistor but also the circuitry to make it flash at
about 1.5 flashes per second. Minimum voltage about
5 volts and a current capability of about 22mA is
required to operate the flashing LED.