Rosco Gels, which color temp works best? in Lighting Posted January 9, 2018 Lighting gels are subtractive meaning that they filter out the spectrum that is not needed so it is not so much the colour temp of the light that is important as the actual source. Tungsten is full spectrum and will give the best results. HMI is also full spectrum but with spikes. LED has missing spectrum and this cannot be filled with gels.