Why we use mercury vapour lamp, arc light or sunlight for photochemical reaction???

Mercury-vapor lamps are light sources with discrete, polychromatic emission (type B). Depending on the pressure used, mercury-vapor lamps can also show a continuous, polychromatic emission. The same applies for certain phosphor coatings for fluorescence lamps. A discrete emission tends to be beneficial, since filtering of undesired wavelengths can be realized …