if your looking for a new bulb then get the red heating bulb, as that doesn't disturb them during the night (they can't see the same light spectrum we can supposedly) and it will raise ambient air temps if thats what you need.
More importantly your going to need some way to measaure how hot your UTH (heat matt) is getting. You need a digital thermometer with probe. Is your UTH regulated, do you use a thermostat or rheostat?
That 23 degrees celscious is fine for the cold side, but it sounds like you have no idea how warm your warm side is :shrugs: