The vast majority of the stuff I write is incredibly depressing as well. I try to write when I'm in a super-duper mood (seriously, after something awesome happens!), then usually I can get slightly better, less morbid results. Good luck.

Well for me trying to access the poetry language is unavoidably tied directly to everything I'm feeling. Which has of late become quite morose as well. I like the idea of writing after something awesome happens, or just thinking about something awesome. I tried it just the other day and love the results. It's good to break out of routine sometimes.
But if you're a playwright then you already know that the poetry language has a huge place in performance, and that skilled use of the darker sides of tragedy has been a staple of great plays for centuries.

I think a lot of what we write is linked to our emotions and it's hard to break past that comfort zone we have set for ourselves. But sometimes, if you attempt to break past that barrier, you will surprise yourself at how much you like the result. I tend to favor writing dark poetry myself but then again I enjoy reading it the most too. I think we all have our styles but that's what makes it interesting.

It's good that I am not alone in my writing style. While I write a lot of different kinds of writing and moods in those writings, I do have a tendency to write darker or more hard material. Especially when I am not very focused or mindful of what I am trying to write. Like musework, when I am free writing, which I normally don't do much of, it tends to get very bleak or scolding in tone. Apparently i am quite angry and it channels my inner jerk! ;)

But I wonder if there isn't some element of my attitude where maybe I want to make sure that I am taken seriously, so perhaps I unintentionally steer clear of lighter content? Hard to tell.