The light within in the context of Earth means awareness of our relationship to Earth. The answer is unique to each person. It's an interconnectedness to all things everywhere. The light within is really an eternal light and we often block it instead of letting it shine through us. It's a love for others and for the environment.
Quakers seek it instead of declaring the truth.
Each person follows it his own way. You express your interpretation in your own actions. It's wisdom as shown through the eyes of people and animals. Every living thing has it. It's something in each one that can be touched.