Luminance and Radiance in computer screen I am currently building a graphics engine. I have a slight confusion on the imaging pipeline of computer screen. My question is how does computer transform the colour in the final frame buffer to radiance on the screen. My assumption is that the final colour in the render target should be proportional to luminance instead of radiance. Then, there is some function in the pipeline that will apply transform inverse of the photometric curve of this value to get the radiance of each RGB value. Am I correct?
1, 1, 1, the output value is white. If this represents radiance than the output should be green, because when the signal radiance is the same, the pixel should be perceived as green. Am I correct?


This is not correct. Your frame buffer most likely contains sRGB values. Of which 1,1,1 is used to represent white. Standard displays do not use spectral radiance values in the frame buffer. sRGB does not map directly or make any guarantees about the spectral power distribution (SPD) of the display. So "G" of 1 does not guarantee some wave with amplitude using W⋅sr−1⋅m−2 centered on the 550nm. Part of the problem is that different type of displays have different SPDs that map to the same perceived color. 

[Evaluation of an organic light-emitting diode display for precise visual stimulation, Ito et. al]
(https://jov.arvojournals.org/article.aspx?articleid=2121657)


Now if you want to physically accurate rendering, you could store all of your lighting values as Radiance with SPDs. As L.C. mentioned, Physically Based Rendering describes that this is done with piece-wise linear functions with like 16+ channels per color. However even if you can get this to be performant, good luck converting all your RGB data into SPDs (there's an infinite # of SPDs for a given RGB value).

Instead what most renderers try to do is to treat the RGB as pseudo-radiance values for the purposes of lighting calculation. This isn't accurate, hence your lighting result changes if you are using Rec.709 or Rec.2020 primaries for instance (if you notice they have different values for mapping to luminance), but it's good enough for real time and even offline in most cases. At this point you can convert RGB Rec709 and Rec2020 values to a single scalar luminance using the Y values of it's primaries.

The Y values of the RGB primaries for Rec709 are:

    R       G       B
Y   0.2126  0.7152  0.0722


https://en.wikipedia.org/wiki/SRGB

Thus Rec709 Linear has the following nits conversion:

nits = dot(linear709Rgb, float3(0.2126, 0.7152,0.0722));


Probably one of the results of doing our calculations in RGB is that G and B add at equal weights, so it's likely to get some color shifting. There was a presentation at SIGGRAPH 2015 from Weta digital that had some examples, but it doesn't seem like the slides are available. As far as I know they are the only ones using a spectral renderer.