So are you saying a 100 Ohm resistor should be enough that the 220k used in the examples is just to play it safe?
Yes. Higher resistance means less current (
Ohm's Law). Resistance means "resistance" to
current flow.
Because I don't have many blue led's I figured to play it safe and use multiple resistors.
It depends on how you connect multiple resistors...
Resistors in
series sum-up and the current will be reduced.... i.e. Two 100 Ohm resistors in series makes 200 Ohms.
Resistors in
parallel reduce the total resistance and increase current. Two equal value resistors in parallel are half the resistance. There is a formula for unequal resistors, but the total resistance will always be less than the lowest-value resistor.
I also noticed that it was much much brighter than the green and red leds
There are a couple of factors at work...
LEDs vary a LOT in efficiency. There are "super bright" LEDs that are much brighter with the same milliwatts. The specs will usually show brightness as mcd at the rated current.... Just looking at my Jameco catalog I see LEDs from less than 10 mcd to over 5000 mcd.
Our eyes have more sensitivity at different colors/wavelengths. (IIRC, our eyes are most sensitive to green).
Power (Watts or milliwatts) is calculated Voltage X Current. So a blue LED at 3V and 20mA is consuming 50% more power than a red LED at 2V and 20mA.