Right well that's what I meant. The circuit I described doesn't implement it and almost two years after I built it for a neighbor it still hasn't exhibited any such hysteresis issues yet. He had to clean off the sensor a couple of times and eventually made a little enclosure for it but other than that the only complaint was that the circuit wasn't quite as sensitive as he had hoped. (I really should have used a comparator but it was done free of charge anyhow so...)I have seen many dusk to dawn lights blink like a strobe light at dawn and dusk... temperature may play into it as well... it warms up and affects values.... Just what happens in real life as opposed to on paper or lab setting.