If you utilize a reduced output lamp and that still isn't suitable to your wife then apply a yellow filter on your lamp. Ideally you want to eliminate any and all stray white light.
Alternatively rather than constructing a filter purchase a yellow output LED. Just ensure that the output is in and only in the yellow range.
This should significantly lower any irritance your wife maybe experiencing while you read. Additionally it shouldn't cause her to wake up fully in the event she does for whatever reason open her eyes for a fraction of a second, even longer.
Our brains do not perceive such light as an indication of daytime or the need to change our waking state.