Chickens lay best 40*- 80* F. That said, they'll still lay at lower or higher temps, especially of they have a draft free and well ventilated coop space.
And I agree, the total hours of light per day is more critical. Ours are on 16 hrs with the extra light added in the morning by a timer. 14 hrs is all that's required. We just use 16 because we don't have to adjust the timer as much when the natural daylight gets shorter/longer during the seasonal changes.
I just started a timer on mine yesterday. I have it set to start at 3:30am and go off at 7:30am. I have 26 hens and I'm only getting 4 eggs a day and I have RIR's. I decided since I wasn't getting that many eggs it wouldn't hurt. If that doesn't work then I know it's the feed I needed to change them to because TSC stopped selling the layer feed I was giving them.
I have a light on in the coop 24/7 also and I get about 10 to 12 eggs from about 16 laying hens. I hens I have in a coop with no light are not laying at all. They are all the same age 24 - 26 weeks. I feel i has helped. I also feed a 18% protein layer feed.
I did have her on a heat lamp because of an egg laying ordeal, but we are in texas and she was not able to get away from the heat of it (she's new and can't be in the coop with the others, so she's in a small dog crate), so we took it away. The temperatures are supposed to drop though, so I might put it back on her.