* Light as a physical phenomenon: In this case, it doesn't really lend itself to a collective noun. We might talk about the spectrum of light or the intensity of light.
* Light as a source of illumination: Here, we might use terms like a beam of light or a shaft of light.
However, there are some creative options, like:
* A blaze of light
* A shower of light
* A cascade of light
Ultimately, the best term will depend on the specific context and the desired effect.