The bitmaps for the lights bulbs are found in the BMPWAV folder and can be replaced or renamed. There are currently round and square lights there already, but you can certainly make your own.
The toggle switch is much like a button and can be any size and has no grey box container. The light bulbs are more like keyboard jog with a grey container box.
There was a time was a light bulb could be any size, but there's a reason for this now. The box is there to contain the bulb of the light to a small screen area. We found that lights can be frequently used, even flicker and will un-knowingly cause the system to degrade performance or hinder screen refresh rates if the bitmap areas aren't contained to a small screen sizes. So we felt we need the grey container box. Live and learn.