@Laurent-Nittler yes, you can dim (and color) every LED separately!
In fact, the bytes you write to the
/dev/ledchainX device correspond to the brightness (duty cycle) of the red, green and blue part of the LEDs (and a separate white LED for SK6812). With this, you can set any color and any brightness.
Let's assume you have WS2813 connected to PWM0, then
echo -en '\xFF\xFF\xFF' >/dev/ledchain0
switches the first LED to full white brightness (255=0xFF = full on for all three R,G,B channels. Whereas:
echo -en '\x7F\x7F\x7F' >/dev/ledchain0
sets all three LEDs to half duty cycle (127=0x7F)
A somewhat dimmed green (red=off, green=160=0xA0, blue=off) would be:
echo -en '\x00\xA0\x00' >/dev/ledchain0
and so forth.
To control more LEDs, just write a longer string to
/dev/ledchain0, 3 bytes for every LED in the chain (4 for RGBW LEDs like SK6812).
Of course, you wouldn't do that with
echo except for the first manual tests, but using some script/program that calculates the string to be sent to