The lens of perception may be interpreted as consciousness. Therefore whatever you hold in your conscious mind colours your lens. Negative thoughts darken the lens while positive thoughts increase light. Both are normal and natural parts of the human experience. Both have value and contribute to the whole.
In order to increase light, adopt a neutral stance and become an observer without attachment. This act alone empowers you in significant ways. Not only will you detach from negative thoughts but you will also have more space for positive ones. For instance, if you enjoy art, you might set time aside each day to explore colours, shapes and textures. If you love music, you might set time aside to explore instruments, song and dance. These practices alone will naturally enhance light in your lens of perception!