How to use light in ui element(image, text...)?

I want to make a 2d game that the player can tap every picture.
The pictures can be spriteRenders or images on the canvas.
Since the picture must be tap, the spriteRender is out.

I know sprite's material set to Sprite-Diffuse, then the sprite can be light.
But it seems it doesn't work on the canvas's stuff (image, text...).

I try LWRP too, but it lows the FPS 60→45.
And LWRP's point light always got a dark line on the radius.

I don't know how touse light in ui now.
Please help : D