As daylight is a mixture of direct sunlight and light from the sky, the spectral distribution changes all the time due to the time of the day and the weather.The standard illuminant D65 corresponds to daylight with color temperature of about 6500K. Incandescent lamps have got a continouus red-dominated spectrum as the light is generated by heating up a tungsten filament.The addition of halogens to the filling gas enhance the efficiency and prevents blackening.Further increase in effiency can be achieved by adding Xenon and / or IRC-coating. Visible region from 380 to 780 nm;height of graph corresponding with relative spectral emission (400mW / klm) per 10nm.