2 sinks? 1 over each sink about 2/3 the width of the sink

Depends on the overall look and design of the area, as well as use. If this is your primary bathroom vanity and it will be used for shaving, make-up application, or other daily grooming, you will want to ensure that the wattage is high enough and make sure there are no colors used on the light shade/globe/cover. I like the look of a light that fills the area between the sinks, faucet to faucet. In your case that would be a light that is approximately 51". The photo shows a more modern light fixture than a traditional, but gives you an overall idea of the application of this idea. There are so many styles available, you would need to provide a photo of the vanity and surrounding area to narrow down the specific style of the light fixture. Also, more modern applications would have two mirrors and you could put light fixtures on either side of each mirror, rather than above, but I like more a diffuse light, so I prefer above the mirror.