I've only had one or two fully lucid dreams. In one I realised I was dreaming, I could not get myself to wake up. I was then convinced I should kill myself to wake up, but could not fully determine if I was sleeping or not, so why take the risk?
Unfortunately, clocks and text seem to work in my dreams. Another reality check is covering your mouth and nose and trying to breathe. Supposedly, this is a good test as in a dream you'll keep breathing. Plus, it's unobtrusive, unlike turning lights on and off at offices and other people's houses.
For me, the best unobtrusive reality-check, by far, has been checking gravity. Just by quickly changing my weight in a chair or rolling up a bit on the balls of my feet, I can see if my weight is there or I start to float a bit.
Checking global light level control (light switches) is, like you say, not unobtrusive. But I've tested, with moderate success, using more subtle lighting features. Window blinds, for example, typically have far more subtle shades of light and shadowing than gets rendered in my dream worlds. Paying a few seconds of focused attention to a window or lamp shade doesn't stand out in most social situations.
Unfortunately, clocks and text seem to work in my dreams. Another reality check is covering your mouth and nose and trying to breathe. Supposedly, this is a good test as in a dream you'll keep breathing. Plus, it's unobtrusive, unlike turning lights on and off at offices and other people's houses.