This SmartMate intellivolt (2 lamp 42watt CFL) ballast runs surprisingly cool trying to run my 18w lamps. With 2 red, & 2 blue on either side. It never achieves full brightness with ANY of my five 18w lamps. The case reaches 30°C after one hour (peak spots) and 31°C after two hours. If you desire 10%-20% less light from your 18w SOX lamps then this ballast might do the trick. Runs the 18W GE lamp at 17watts of power. Runs the Philips SOX-E18 lamps with only 15watts consumed.