I built a small night light that turns on when the room light is turned off, glows for a bit and then dims down, giving me enough time to find my bed, in what used to be pitch black darkness, once I turn off the lights.
It works as advertised. LDR connected to an ATtiny45, driving a few LEDs through an ULN2003. The only thing that somewhat bothers me is the fact that LEDs don't light up the moment I turn off the room light, but it takes about half a second (eyeballing here). When I envisaged this project in my mind I had an image of it turning on so fast that the delay is not noticeable, yet here it is. Certainly less than a second, but noticeable.
To troubleshoot I added detection of turning on the lights, and it seems significantly faster.
I found some old datasheet for an LDR (not the one I'm using), and surprise, surprise, rise and fall response times differ by the factor of 4-6 (depending on the model), but are still below 90ms (usually below 35 ms) on the slower end.
So, while this is more of a rant than a cry for help, is there a way to decrease the response time? Phototransistor, maybe?