Not sure what you mean here, do you mean you are trying to display a close domain, already formed image?
The thing is, the ratio between RGB:
Because some channels are “clipping”, the ratio outputted that you see on the screen will never be automatically the same as the open domain scene reflectance. It has to be engineered depend of the output medium instead of focusing on the scene reflectance. The thing here is called “intensity based gamut mapping”. And the questions Troy asked about how should a very bright blue looks like is directly related to this.