Despite their long history in studying the mind, consciousness is still a controversial topic under philosophers. However, philosophy can consider something like "experience" wherefore science has no measure of.
David Chalmers uses experience in his approach on consciousness. He introduced the term of the "hard problem" of consciousness. Essentially, he divides consciousness into two part. The complementary part, the "soft problem" summaries those internal states which can be felt, while the hard problem describes the phenomenal experiences. Chalmers argues further that the hard problem can never be explained.