'patch of light' is correct and usable in written English.
You can use it whenever you want to refer to a small area of light in a dark environment. For example: "She was sitting in a corner, illuminated by a small patch of light coming from the window."
The button was nothing but a patch of light on the palette.
A small, bluish patch of light appeared at the end of the receiving tube.
If you take a look on a very clear night at the constellation of Andromeda, a little fuzzy patch of light is just visible with the naked eye.
Like the headlight of a distant, oncoming car, this little patch of light will slowly brighten and sharpen over the eons.
And that patch of light was the sun, as high in the sky as it gets in early December at the Netherlands' latitude.
Director Elizabeth Freestone rightly opts for a simplicity of staging: a shadow looms out of the darkness; a patch of light suggests a bedroom door ajar with possibilities.
It is there that light is processed by the retina: a patch of light-sensitive photoreceptor cells that sends signals down the optic nerve to the brain.
In a species whose eye amounts to nothing more than a primitive patch of light-sensitive cells, a mutation that causes this patch to fold into a cup shape might have a survival advantage.
The vitreous connects to the retina, the patch of light-sensitive cells along the back of the eye that captures images and sends them to the brain via the optic nerve.
"You see that circle there?" he says, pointing to a patch of lighter tan near the top.
The ultra-distant galaxy, known as CR7, has a massive population of young stars, and a nearby patch of light-emitting gas that may not have yet formed a single star in it.
