Abstract In this study, we aimed to determine an ordinary/empiric/standard phototherapy treatment protocol for duration without controlling total serum bilirubin (TSB) levels after initiating phototherapy in early-term and full-term jaundiced newborns who had no hyperbilirubinemia neurotoxicity risk factors. We compared two groups, each receiving either 24 h (Group I) or 18 h (Group II) of continuous phototherapy in terms of demographic characteristics and efficacy (rate of decrease in TSB levels with phototherapy). No control TSB measurements were performed in the study groups until the end of phototherapy for the predetermined durations. Declines in TSB after phototherapy were significantly greater in Group I than in Group II, both in terms of mg/dl (11.81 ± 2.93 mg/dl vs. 10.75 ± 2.48 mg/dl, P = .0008) and percentage (56.71 ± 9.06% vs. 52.86 ± 8.37%, P = .0002). However, the rate of TSB reduction after phototherapy in mg/dl/h (0.59 ± 0.13 mg/dl/h vs. 0.49 ± 0.12 mg/dl/h, P = <.0001) and percentage per hour (2.93 ± 0.37% vs. 2.36 ± 0.46%, P = <.0001) were significantly higher in Group II than in Group I. This indicates an inverse time-response relationship between the duration of phototherapy and the response rate in the study groups. Although the 24-h phototherapy course showed greater efficacy concerning the primary bilirubin outcome measures (decline in TSB in mg/dl and %), the 18-h course of phototherapy treatment provided better hourly outcomes and reached its saturation point around the 18th hour. Therefore, an 18-h phototherapy without TSB monitoring until the end of the phototherapy should be considered for jaundiced newborns lacking neurotoxicity risk factors.