This all started with a borrowed spectrum analyzer (Thorlabs CCS100, 350-700nm, <1nm resolution). I started measured spectrum of every LED and light source I had around... :

Daylight spectrum:

Just blue light from sky (not including Sun) - we can see it is blue-cyan:

My nuclear light fixture HID lamps were quite funny. Right after turn on - lots of mercury lines:

Heating up...

And it's done:

Cyan LED:

Blue 460nm (from RGB):

Green 520nm (from RGB):

Red (from RGB):

And finally white LED: