The size of the lights does not matter as much as the bulbs specified by the manufacturer.

If the fixture uses A19 60W incandescent bulbs, each bulb would give ~ 800 lumens. If 100W incandescent bulbs, ~ 1600 lumens per bulb.

A quick way to figure things out is to calculate the amount of light required based on a lumen per sq ft calculation

For example
13 * 13 * 35 (lumens per sq ft) gives 5915 lumens.

Size will work, but the best way is use LED light, I think it is best, I use it at my house.

Here is a link that might be useful: decorative wall plaques