Grammahen, ceramic bulbs are easily available in 100 watt - check your pet store (reptile section) or ebay. They are spendy, but last a long time.
I am no expert on this, but I am thinking that the chicks didn't go in because the light was on. With a light, their day/night rhythms get somewhat out of sync. Without a light, they can tell that the sun is going down naturally and it's time to put themselves to bed before it gets too dark. Chickens do not have good night vision. I'm guessing that this is why they huddled in the coop and cried when the light went out - it was sudden (daytime, uh-oh, now night) and scary inside (too dark!) and they wouldn't be able to see to get to the roost.
If it was me, I would definitely turn off their light and connect a ceramic heat bulb to your heat sensor. It will need to go over your roost as ceramic bulbs do not heat air, they heat surfaces (like chickens). This will provide them warmth when they need it but keep their natural day/night rhythms in tact.
Good luck - I can tell that you're a good chicken gramma.
I am no expert on this, but I am thinking that the chicks didn't go in because the light was on. With a light, their day/night rhythms get somewhat out of sync. Without a light, they can tell that the sun is going down naturally and it's time to put themselves to bed before it gets too dark. Chickens do not have good night vision. I'm guessing that this is why they huddled in the coop and cried when the light went out - it was sudden (daytime, uh-oh, now night) and scary inside (too dark!) and they wouldn't be able to see to get to the roost.
If it was me, I would definitely turn off their light and connect a ceramic heat bulb to your heat sensor. It will need to go over your roost as ceramic bulbs do not heat air, they heat surfaces (like chickens). This will provide them warmth when they need it but keep their natural day/night rhythms in tact.
Good luck - I can tell that you're a good chicken gramma.