Grumpy_Mike:
Okay NOW I think I understand why you would need a LOWER resistance for 10 LEDs than for 1 (3.3V=x150Ma(10 LEDs15Ma each)). Therefore x=a 33? (or the next larger value)resistor.
Still wrong?
The maths is right but the electronics behind it is wrong. You can not use one resistor for more than one LED because the forward voltage drop of each LED is slightly different. So therefore each LED needs its own resistor.
Yeah, this is the usual consideration, but have you ever actually tried using just 1 series R
for multiple Leds? I'm just curious as to the actual results.
Also, I am assuming ...... that 15Ma is the amount of current needed for an LED to turn on.
For a start it is milli Amps mA not mega Amps MA. Second no there is no set amount of current to turn on an LED, the smaller the current the dimmer it is. I have a white LED that is too bright to look at directly when it only draws 3mA. It depends on the specific LED. There is however a minimum voltage required to turn it on, normally called the forward voltage drop.
Yeah, Leds come in old style [ie, poor efficiently], plus the newer medium- and high-output
devices. The latter will produce a lot of light for a couple of mA.