What is light before we see it?
For Berkeley, everything that has not been perceived doesn't exist, but light needs to exist unperceived before it reaches the eyes. How is this possible in Berkeley's idealism?
I am not aware that Berkeley's offers an account of light at any length outside his 'A New Theory of Vision' (1709). He there refers to light as consisting in 'rays':
... the particles which compose our atmosphere intercept the rays of light proceeding from any object to the eye : New Theory of Vision, §68. This language is entirely typical of the way Berkeley talks of light throughout the text.
Always he uses the language of 'rays' of light proceeding - travelling, moving - towards the eye. It is not clear how, if there are only minds and their ideas, ideas can 'proceed'. Ideas can't literally move, surely : proceed from one spatial location to another.
The only way out seems to be to say that God creates certain ideas which we experience as light. As created by God and preserved in existence by God, and perceived by us, these ideas are never unperceived.
While I think this is what Berkeley should say and does believe, his language of rays of light 'proceeding' from object to eye is physicalist and cannot be taken literally from his own viewpoint. Here does, indeed, think with the wise and speak with the vulgar (Principles of Human Knowledge, §51).
Considering that light is an object, and the observer is the subject, what Berkley means is:
light needs to exist unperceived before it reaches the eyes.