A long table is the hardest thing in the house to light. Overhead light flattens the food and puts shadows on everyone's face. Too many candles and half the guests are looking at each other through a flame.
The good news is that the fix is mechanical, not artistic. It comes down to two measurements.
Below the chin or above the head
Light sources at eye level are the problem. Anything between roughly 30cm and 120cm above the tabletop sits in the line of sight and makes conversation across the table uncomfortable.
So keep flames low — under about 25cm — or lift them high, on tall candlesticks that put the flame above head height. A table with low votives and one or two tall holders reads as considered. A table with a row of medium candlesticks reads as an obstacle course.
Hurricanes are not just decorative
A glass hurricane or cylinder does three useful things: it stops the flame guttering when someone reaches across, it keeps the light steady rather than flickering into people's eyes, and it lifts the glow slightly so it spreads across the cloth. If your candles keep blowing out during dinner, this is the answer, not thicker candles.
Space them like place settings
A common mistake is clustering everything in the centre. Light travels less far than you think — a small flame lights about 40cm of table convincingly. On a table for eight, three or four low groupings down the length will do more than one large centrepiece.
Leave the last 20cm at each end clear. Nothing kills the look of a table faster than a candle competing with a serving dish.
Pendant height, if you have one
If there is a fixture over the table, hang it 75–85cm above the tabletop. Higher and it lights the room instead of the table. Lower and tall guests will meet it. Dim it to roughly a third once people sit down; its job at that point is to define the edge of the table, not to illuminate the meal.
The last thing to check
Sit down in each chair before guests arrive. Nine times out of ten, one seat is staring straight into something. Move it 10cm and the evening gets longer.