A lot of important things happened in '79, including the Sandinista and Iranian Revolutions. That year was the beginning of the end of a revolutionary cycle: the great wave that began with the Great Spring Victory in Vietnam, and ended with the unfortunate stalemates of El Salvador and Guatemala.
In one sense it's easy to see Lynn's novel as part of that wave. It was a late '70s mainstream SF novel with perfectly "out" and untroubled LGBTQ individuals. Not to mention "polycules" all over the place!
Those weren't easy times to be "out" as an LGBTQ author or to write SF with "out" characters. After all these years, I still remember the derision that an Ares reviewer brought to the back cover blurb for Lynn's Watchtower: "An Adventure Story for Feminists and Humanists." I went right out and bought that book! No regrets!
So what was the back cover blurb for A Different Light?
"Jimson had twenty years to live. Or one."
Jimson is a young adult on a backwater world. He's a successful artist, rather than a farmboy, but one might think he's a bit of a whiney Luke. Jimson's unhappy because he feels stuck on the planet New Terrain. He has a genetic disease which is treatable there (and really on any civilized world or space station) but which will explode into uncontrollable mutations if he goes into the Hype (i.e., hyperspace).
So that's bad.
I actually had to check myself on the perception that he's whiney. That perception is a form of biological/health-based privilege. Ableism if you like. Jimson has a right to feel stuck and whiney.
And Jimson has another reason to be unhappy too. His first lover, Russell, took off a number of years ago for space. Russell didn't stay in touch, either. Jimson has a double loss going on.
So of course, Jimson is going to go off into the Hype to look for Russell.
Jimson hangs out in a spaceport and soon meets Leiko, a female spacer who becomes his lover. He makes art and hangs out in a spacer bar. Jimson makes friends with a number of other spacers.
It's worth a short digression to point out that Lynn's spacers have a culture apart from others in society. They have their own social rules, such as no questions. Spacers offer information about themselves to others only after a greater sense of intimacy/affinity/trust has been established. So we have the social anonymity of the big city/port city; the social nexus for the emerence of LGBTQ cultures. Here you can see traces of the lineage that began with Samuel R. Delany's working-class spacer/outsiders - and presumed sexual outlaws (1) - from Babel-17 and Nova. This lineage passes through Lynn's work and eventually leads to the protagonists in Melissa Scott's novels.
Jimson and Russell reunite. They have an adventure together. Jimson, star captain Russell, and his two hired crew go off to plunder religious artifacts from a primitive planetbound tribe (2). They are classic space assholes worthy to be PCs in virtually any Traveller RPG campaign.
Other things happen.
Jimson's cancer mutates with a vengeance. There's no magic cure, but the novel has a very interesting, open ending.
Something important occurred to me after I finished reading the novel. Just a few years after the publication of A Different Light, I had a significant life-changing experience that gave me something in common with Jimson. I met my first lover, and all too soon, he simply went off into space too. The silence became unbearable. I felt alone for a very long time - for years, in fact.
Thank god for my comrades in the Central America solidarity movement of those days; only a few really knew how how to support a gay comrade in the early '80s, but they helped me live in different ways and experience things greater than myself; things worth living for.
They helped me see a different light.
(1) See the sexual outlaw aka gay ubermench in John Rechy's City of Night. Delany more or less lived/endorsed the practice without embracing the ideology.
(2) I'm reasonably confident that Iain M. Banks lifted and twisted this scene Banks-style for Consider Phlebas.