The use of light, either chemical or battery powered plays an important role in catching swordfish. There is no question that the use of artificial light increases the probability of catching a swordfish.
Swordfish have giant pupils, about the size of a racquet ball which makes them extremely sensitive to light. Swordfish are designed to be able to see in extremely low light conditions, this is why they are efficient hunters is the deep depths of the ocean.
Putting a light on your line while swordfishing acts as an artificial magnifier to make your bait spread seem larger then it is and the light attracts attention from both swordfish and bait schools in the area.
Each color of light in the spectrum we use has different qualities. For example, each color of light has a different quality of brightness and water penetration. Water penetration means, how far of a distance the color of light can travel through water before it disappears. The colors in the spectrum which disappear are, from first to last, Red, Green, Blue, and Purple.
Now, when placing your artificial light onto your fishing line you want the light to be far enough away that your bait will be sitting right outside the lights brightest sphere in the shadow line. In terms of what light color is the best depends on any given night, as swordfish seem to have patterned bites based on light color as well as depth. Although, there is a much higher probability for bites on the colors blue and green.
When the moon is full and there is a lot of light penetrating the water column the light on your shallow baits will be diminished due to the large amount of natural light penetrating the water.
Captain Vinnie LaSorsa