Here in northern California, the outdoor temperature is between 95 to 105 degrees during the day right now but the weather drops to the 70's at night. I went to a feed store yesterday. This particular feed store keeps all of their chickens out back outside of the store. The feed store is owned by a local vet and the vet has an office that connects to the feed store. The staffs are pretty knowledgeable (not your common feed store is my point). I bought a few baby Danish Leghorn chicks from them yesterday.
The feed store had them with no light which had me ask - "You know if you read online, it all says they need a heat lamp until they are few weeks old. No light?" Guy laughed ..."its 100 degrees outside!"
All of the chicks did look more than fine. I threw my two week old chicks outside last night with no light and they did just fine this morning. I am starting to wonder if the "must use a lamp/keep them indoors" is not true for summer when the air temperature is in the 90's/100's.
Either way – I have 2 week old chicks outside with no heat lamp and they seem to love life!