The most prominent imagery in “The Lagoon” is darkness. The story begins with the sun setting, and Conrad painstakingly describes the darkness of the rainforest surrounding the lagoon, which as it often does, symbolizes the unknown. The jungle, once enshrouded in darkness, feels ominous, looming unexplored and obscure. 

As they travel to Arsat’s clearing, it seems that “darkness oozed out from between the trees.” The crew of the ship also goes largely undescribed, presumably because the narrator and the white man know very little about them. Instead, they are characterized quite simply, described through their “slender and distorted shadows”—just as the jungle, these dark figures are mysterious, unknown, and frightfully foreign. 

It is only when the canoe reaches Arsat’s lagoon—a clearing familiar to the white man—that the images of the dark jungle recede and readers see a “strip of bright-green, reedy grass to frame the reflected blueness of the sky.” This is an especially strange description of the lagoon, as the narrator has confirmed that the sun was setting before the characters reached the clearing. Here, it is possible that Conrad has chosen to forego consistency in the story to maintain the light and dark dialectic that reflects the known and unknown.

One of the strongest examples of this light and dark imagery is at the end of the story, after Diamelen takes her last breath. Although the sun has begun to rise, Arsat says that now that his love has died, he can see only darkness. The story ends with him “looking through the great light of a cloudless day into the hopeless darkness of the world.” Darkness, both physical and emotional, has consumed him. 

As Arsat gropes his way through the darkness of his grief, his future seems unknown—all he knows is that the love of his life has died and, now, he must avenge the brother he loved and betrayed. How and when he will do so remains unclear, hence the feeling of emotional darkness. Without light, Arsat remains embroiled in misery and uncertainty, unable to gauge what his future might look like. 

Throughout the story, there are occasional contrasts drawn between Western and Indigenous ways of being in the world. This theme appears, for instance, when the group arrives at Arsat’s lagoon. The rowers are afraid of Arsat because he has fixed his house and moved in, rather than built it brand new; the local belief is that the ghosts of previous residents inhabit old houses. Thus, the rowers do not trust Arsat. The narrator offers further commentary on their belief about the white man, and why he would not fear Arsat in the same way that they do: 

White men care not for such things, being unbelievers and in league with the Father of Evil, who leads them unharmed through the invisible dangers of this world. 

Arsat makes a similar comment when he reunites with the white man. Arsat remembers when he first met the white man, and then the white man left: “You went away from my country in the pursuit of your desires, which we, men of the islands, cannot understand.” In both cases, the motivations of those from the West and those from the island are completely different. All of the characters in the story are, in some way, aware of this difference.

Still, Arsat makes a comparison between his own people and white people, saying: “We are of a people who take what they want—like you whites.” While there may be fundamental differences in beliefs and motivations, there is something that unites these very different cultures, namely taking what one wants. While there are plenty of differences between these cultures, there are occasionally similarities. Conrad draws the comparison in the wake of so many contrasts to bring to light the fact certain human traits are universal to all people, even despite cultural differences.