A color temperature modulating method involves: computing blackbody spectrums including a target color temperature, and performing normalization at a benchmark wavelength to define a common color-temperature area; selecting a white LED containing phosphor; adjusting the white LED's intensity such that the primary-peak wavelength is close to a maximum relative intensity in the common color-temperature area accordingly; using a blue LED, a green LED, and at least two red LEDs, wherein peak wavelengths of the blue and green LEDs are located between the primary and the secondary wavelength of the white LED, and peak wavelengths of the red LEDs are greater than the primary-peak wavelength; and adjusting relative intensities of the blue, green, and red LEDs to make a relative intensity of a combination of these LEDs and the white LED close to the target color temperature.