Technically I'd give this one 2 1/2 starts out of 5, but seeing as that's not an option, I'll be generous for two reasons:
1) Light-Source's plot predates the energy concerns of its time and of the now. It's touches upon global warming themes quite heavily for a novel published in 1985, all of which are relevant today Neat.
2) While the story starts off slow (the first 100 or so pages are a chore) after the initial set-up is finished and we it's quite a brisk run to finish from there on in.
Emily, the protagonist isn't incredibly interesting (though her work as a scientist is) BUT this changes quite rapidly and Bari Wood's does a commendable job of fleshing out a rather simple character into a true hero as the story progresses. Still, the plot is the true main character here and it's good enough to keep you interested in what happens next.
That said, I do wish Wood had made her Emily into more a flawed character, especially seeing how the story makes a sudden shift from a global threat to a much more personal towards the end. Although I suppose that's her flaw, Emily's much too focused on her work to notice much in the way of the personal. Clever, especially once the true antagonist is revealed, but not always compelling in terms of a leading lady.