Great question and John’s answer is pretty much right on I’d say- it’s all about energy and display brightness.

You may be interested in the rec.2020 spec that is being proposed for UHDTV broadcast. This spec uses a very wide gamut, almost along the lines of what you describe. I wrote about it last year here: http://dot-color.com/2012/12/04/so-you-bought-a-4k-tv-now-where-is-the-4k-content/

This standard cannot be achieved without laser or maybe quantum dot backlight technologies.

What you are suggesting is sound, just not terribly feasible. IF power were not a concern, you could get a huge gamut with three monochromatic light sources as you have suggested. But there are two little problems.

The first problem is that our eye is not particularly sensitive to light around 400 – 450 nm or getting up close to 700 nm. You would consume a lot of watts of power to get the display bright enough.

The second problem lies in how you create that monochromatic light. If you start with LEDs (either white or RGB), you need to pass the light through filters in order to get close to monochromatic light. This can be done, interference filters can be made that pass very narrow ranges of light. The narrower the band pass (that is, the closer you get to monochromatic light), the closer you get to the outer edge of the horseshoe in the chromaticity diagram, which is what you want. That’s good, but the narrower the bandpass, the more light you need to throw away. This is somewhat more of a problem with white LEDs than RGB LEDs, but it is an issue for either. There is a fundamental tradeoff between three things: a bright display, a display that has a big color gamut, and having a display that consumes lots of power.

It is theoretically possible to build a “flying spot” display that uses three lasers that are rastered across a screen via spinning mirrors and that are modulated to create the picture. Being lasers, they would be very pure in color. I am not aware of anyone who has built such a thing. Might be fun, though!

John

I learned a lot from your explanations; still I do not catch the complete picture I guess…
The question that burns the most in my mind is:
Suppose a display manufacturer wants to make a display based on 3 colors and wants to have the largest gamut….. Would it not be best to pick 3 colors that are located as far apart as possible in the diagram? Lets say 450, 520 and 700 nm?Is this reasoning correct, but is it difficult to get monochromatic light sources, or is my understanding of the matter still lousy?

Regards,

Joeke Noordhuis