For leopard geckos, ground temperature is important rather than ambient air temperature. In the wild they would come out in the darker hours and lie on rocks/substrate that have been warmed by the sun throughout the day - heat mats replicate this. Any colour light bulbs can still be seen by leopard geckos, so would disrupt them if you were planning to use this during the night - most are not willing to come out in the day to bask under them so they won't get the heat they require. Heat mats really are the best option for this species
If you do still choose to use a heat lamp make sure it is also on a thermostat (as the mat should also be) to prevent over heating. You would also have to keep a close eye on the cool end, as you said, in a 2ft viv it is going to make getting an effective thermogradient difficult.
If you haven't already read about it, thermostats are not accurate for measuring temperatures so should be used along with a digital (not analogue) thermometer to get the correct temperatures.