(aka Attention, Awareness, Sati, Mind (capital M) and The Thing)

It's like the beam of a flashlight in a dark room. Where you direct it you see, where you don't you don't.

You direct your Light at experience-things (perceptual phenomena). Sights, sounds, thoughts, feelings etc.

You can focus it, narrow the spot of light.

You can relax your focus, let your Light spread out wide.

When you focus your Light upon a thing that thing reveals more about itself (why?).

When you focus your Light upon one thing other things become less visible.

When you are trying to focus your Light upon X, and you are distracted by Y (the demand for your attention is irresistible), your Light is pulled, against your will, from X to Y.

When you lose control over your Light, over your ability to direct it and focus it (because you are drunk or upset, or doing that Growing technique), new stuff becomes visible. 

When you entirely withdraw your Light from a thing, when you ignore it, that thing becomes invisible.

When you focus your Light intensely upon one thing that thing becomes beautiful, or at least very significant.

When you focus your Light intensely upon one thing all the other things become invisible.

When you are upset your Light is upset and you see less clearly.

When you are calm your Light is calm and you see more clearly.

(Your Light is you, maybe.)

You direct your Light at important things and ignore unimportant things. That which you direct your Light at offers important details and implications, further demands for attention. That which you ignore does not. So you see how these things can spiral. Rabbit holes can be constructed.

Light plays a key role in the construction of your reality. The visible and invisible. The significant and insignificant. The beautiful and ugly.

Light is formless. Like a cloud or a blob of water. It can take all kinds of shapes and move all kinds of ways.

It is what we manipulate in meditation.