The premature debonding of Fiber Reinforced Polymer (FRP) sheets has been well studied and documented for normal weight concrete. This type of failure mode can be averted by keeping the maximum FRP strain below the debonding strain in the FRP as specified by ACI 440.2R-17. However, the debonding strain in light-weight concrete has not been addressed or evaluated yet. Accordingly, this present paper investigates the characteristics of the debonding strain in light-weight concrete using full-scale reinforced concrete T beams strengthened with different levels of carbon fiber reinforced polymer (CFRP). These beams were prepared and strengthened in two series. The first series included three T beams (T1LW, T2LW and T3LW) that were cast with lightweight (LW) concrete. Beam T1LW was tested as a control, beam T2LW was strengthened with 2 layers of CFRP, and beam T3LW was retrofitted with four layers of CFRP. Series two consisted of three other T beams (T1NW, T2NW and T3NW) that were strengthened the same way as series one, but with normal weight (NW) concrete. Both series had identical cross section geometry, reinforcements, span length, concrete strength, and FRP properties. The debonding strains of the lightweight and normal weight concrete are compared, and the validity ACI 440.2R-17 equation for lightweight concrete is evaluated.