With usual Rec 709 primary colors most common approach is to use simple wide spectrum light source (like white diodes) and just filter out necessary light using subpixels. It is very cheap, good learned and stable thing.
For Rec 2020 (and similar color spaces) for display you need narrow color source or quantum dots with wider source. Problem is - narrow sources need thermal stabilization to make your primary colors stable :-) And quantum dots have their own issues besides capitalists who use patents to jack their prices.
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