A lutetium-based phosphor having the chemical formula: xLu3Al5O12.yGd3Al5O12:CePrEuTb, and being capable of radiating reddish orange-red spectrum when activated by a shortwave light emitted by an InGaN light-emitting diode. The invention also discloses a warm white LED using the lutetium-based phosphor that produces orange-red light having the peak wavelength λmax>560 nm, half width>125 nm and color rendering index Ra≧75 when activated by the LED radiation λ=420˜500 nm.