Treat dilated leg veins - the vascular lesions which cannot be removed by IPL 

To clear leg veins, the vessels must be constricted. A 1064 nm wavelength Nd:YAG laser sends energy into the blood and vessel walls, where it is absorbed by blood. Red blood cells are heated, causing met-haemoglobin formation and greater absorption. This causes microclotting and heating of the vessel wall, leading to complete or partial collapse. The constricted vessel then degenerates, and the visible leg veins disappear from the surface of the skin.

Treating vascular conditions in general is based on the principle of selective photothermolysis performed with a single pulse.
A condition of good results is that the Pulse Time is chosen noting the thermal relaxation time for the actual vessel thickness.
The ideal immediate response to treatment with vascular laser is coagulation of the vessel with no other apparent effect. This effect can be observed in the form of bluish or grayish discoloration visible on the skin surface. In leg veins, blanching or disappearance of the vessel may occur.

Leg vessels are normally deep, which is why Nd:YAG in most cases responds better than IPL.
I²PL is good for treatment of very superficial small vessels or blanching after sclerotherapy. Note that lasers or light can only be used 1 month post sclerotherapy.