A one-year field study compared the conventional 250W IR heat lamp with an energy-efficient 175W radiant heat lamp for swine farrowing operations. The energy-efficient heat lamp showed a $36 annual cash savings per unit (assuming $0.10/kWh electricity); a 1.2% absolute reduction in piglet mortality from birth to weaning (5.0±0.28% vs. 6.2±0.44%) (P<0.01); a 45% lower lamp failure rate (18±4% vs. 32±3%) (P<0.05); and a slightly higher rate of weight gain for the piglets (217±4 g/day vs. 211±4 g/day) (P>0.05). The possible benefits of using the energy-efficient heat lamp include an annual energy savings of $5,400 and 284 more weaned pigs for a 1,000-sow farrowing operation. The study also revealed circadian patterns of thermoregulatory behavior of the piglets, i.e., higher heat lamp usage during the day and lower at night. Both the frequency and the magnitude of heat lamp usage seemed to depend on heat lamp size and piglet age. Particularly, piglets spent more time under the 175W heat lamp than under the 250W heat lamp, although visits to the heat lamps decreased with piglet age in both instances. The results suggest that to accommodate the progressively decreasing thermal needs of the piglets, a variable-output heat lamp would be more suitable than a constant-output heat lamp. Further research is warranted to quantify the dynamic thermal needs of the piglets during this critical phase of their life cycle.