The main purpose of a pendant light fixture above a kitchen island is to provide task lighting for that specific surface area. These pendants are not meant to illuminate your whole kitchen...
They are meant to provide specific lighting for the task at your island. You may be washing at your island or cooking or prepping and maybe even eating at your island... All of these tasks require task lighting.
Beyond that, pendant light fixtures are a great way to bring some real design appeal into your kitchen. They can be delicate and discrete or dramatic and eye-catching or anything in between.
typically you have lighting at the ceiling like recess pot lights that provide general illumination but you need to bring additionnal lighting down and focus that spread of light onto your island surface and evenly distribute that light across the total length of your island wich means math.
The first number to keep in mind is the distance between the underside of the light fixture and the top of your kitchen island surface that space is in beetween is key to making sure you have a visual connection between your island and the pendant light fixture above that number should be between 30 to 36 inches.
Because the pendant is illuminating a specific task you want that clear space you feel comfortable at the island and it doesn't feels like the fixture is too low that it may get in the way.
If the fixture is too high that focused light is less focused on the surface and the light fixture is visually disconnected from the island. It's like there are two separate features in your kitchen instead of one cohesive feature element.
You want your island and your light fixture above to be visually connected to one another
Size & Quantity
The next thing to consider is the size of the fixture itself and how many of the fixtures you'll want to hang above the island and yes more math.
If your fixture is quite large then , maybe one is all you need. Consider its visual weight as well as its actual measurements in determining if one fixture is sufficient.
A large solid looking fixture is a great way to create a dramatic element in your kitchen and you won't need more than one to do that.
If you prefer to create something more subtle. Then consider small fixtures that cast a small spotlight on the island surface.
These small pendants are no usually any bigger than eight to ten inches in diameter. Hanging several of these fixtures will provide even light flow along the length of your island and will allow your eye to see past these fixtures beyond.
In this case, it's important to space these fixtures apart leaving anywhere between 12 to 18 inches of space between them. Depending on the overall size of your island.
I would caution you to limit the number of fixtures like these to four or five as too many small pendants may start to look cluttered in the space and then there's always the in-between sizes.
If your pendant light fixture is between 18 and 24 inches wide, then you'll need to calculate the space between the fixtures and figure out if you can fit two or three above your island.
A good rule of thumb is to allow for 24 to 34 inches between the fixtures and it's a good idea to have almost 12 inches of space from the ends of the island as well.
A typical 8-foot island will look great with two medium-sized pendant light fixtures above.
Now, these are just guidelines and the actual spacing can alter depending on the space, the length of your island, and of course the type and size of your fixture.
And finally, one other key consideration is visual weight and how you want your kitchen island to fit into your overall kitchen aesthetic.
If you want your kitchen island to really stand out from the rest of the kitchen then consider light fixtures that have a distinctive material or color or a definite shape.
Solid fixtures with shades draw more attention than open fixtures where you can see right through them. They will have more visual weight and they will draw your attention to the lights and the island.
Fixtures that stand out from the background will have more visual weight bring more attention to the island first and foremost.
If you'd prefer to have one overall cohesive kitchen where you'd like to see the background, the kitchen cabinet beyond, or maybe your focal point is the range hood instead then consider using fixtures that are clear or open like these.
Because these fixtures are more open and you can see right through the fixtures themselves they tend to look lighter in visual weight and they just don't command the same attention.
So here's your takeaway: pendant light fixtures above an island are what dreams kitchen are made of, make sure to visually connect the light fixture to the island by keeping the comfortable space above the surface of your island.
Consider the sizing of your fixtures and determining how many light fixtures you'll need to provide even light flow along the length of your island and finally consider the materials and visual weight of the light fixtures to achieve the look you're after dramatic and attention-grabbing or clear and cohesive, it's totally up to you.