Powering many LEDs

What is the best way of powering several LEDs on the same time?

Whitout using LEDs with built-in resistor
Without using a resistor for each LED in parellel
Without using matrix technology powering one at a short time each
Without couple LEDs in serie where the power has to be high for powering e.a. 100 LEDs

Maybe one of the upper techniques are used for that purpose

Series circuit.

Say for 10 Red Leds (at10mA) makes 10 x 1.7 is 17 volts.
Use 24 volts DC supply, then a 700 ohms resistor is required.

On AC 24 volts an other string of leds can be wired antiparrallel so 20 leds can be connected with one 700 ohms resistor (680 R)

a 1/4 or 1/2 watt resistor will suffice.

Other colour leds have different voltages for running and vary between 1.7 and 3.7 volts, check led data sheet.

As long as led current for normal leds stays below 20 mA's there will be no problems.