Ceramic bulbs emit only heat ensuring that chicks have a natural growth rate and aren't kept awake 24hrs a day.
Red light bulbs draw vitamin A from growing chicks which can result in 'curly toe' and other bone disorders which is why you'll never see one for sale here.
Fits into standard screw fitment, best used with ceramic holders due to the heat generated which may well melt plastic fitments.
Costly but these last for years as there's no filament.