Hi,
I need a LED (14 of them, indeed) which is small (not more that 3 cm, exclusive of pins) and has a power halfway between the LEDs used for illuminate a room and the little LEDs commonly applied on a breadboard. I need to use it with Arduino Mega 2560.
Does it exists such type of LED? Can I found it on eBay?
Thanks 
3mm thru hole? 5mm? 8mm? 10 mm? SMD? 30mm (3cm) would be huge. Browse here
http://www.dipmicro.com/store/index.php?act=viewCat&catId=511
or here
https://www.superbrightleds.com/cat/component-leds/
Brightness will depend on the current limit resistor you use for each one.
(5V - Vf)/current = resistor
where Vf is the voltage across the LED when it turns on. Somewhere like 2.2 to 2.7V for Red and 3.2 to 3.7 for Blue, White. Gree, Yellow, other colors will fall somewhere in between.
alexander79p:
I need a LED (14 of them...I need to use it with Arduino Mega 2560.
Seems you want to power them from a Mega.
Arduino pins have current limitations, the chip has a 'total current' limitation, and the onboard supply has limitations.
If you want to connect 14 medium-power LEDs to an Arduino, e.g. 1watt star bases, give them their own supply. And switch/control with an external transistor.
Tell us what do you want to do with these LEDs.
Maybe there are other solutions.
Leo..
There are these 10mm 0.5W leds available now. I have never seen one myself. They draw 100mA each, so you will need some transistors to drive them, or a chip like tpic6c595.
I have to let those LEDs to turn on in sequence, something like this:
The LEDs should have many levels of intensity (only ON/OFF is not suitable), so I need something like PWM:
I have to control the intensity of the LEDs instant by instant. I already know how to do this: I have made a prototype in which a Java program communicates with Arduino Uno through a USB port, and every 50 millisecond updates the intensity for 3 LEDs with a value between 0 and 255. I have to replicate a similar mechanism in this project.
Something like this?
Digital LEDs, RGBW, 4x20mA each, with inbuild 4x 8-bit PWM.
Leo..
@Wawa: Fantastic! The product from Adafruit you suggested seems to fit exactly to my needs 
Thank you very much, and thanks to all for the help