Laser is characterised by its wavelength, which is measured in nanometers (nm). The wavelength determines the colour of the laser light. Absorption of energy in the melanin of the epidermis (the outer skin layer) drops as the wavelength increases (dotted curve). However, absorption of energy in blood cells depends on the wavelength of the laser in a highly non-linear relationship. This is illustrated by the solid HbO2 curve.

Absorption peaks twice in the therapeutically feasible spectrum - at around 532 nm which is the common green laser, and at around 589 nm which is the yellow laser. From a clinical viewpoint, the yellow laser is the optimal choice for therapy because it deposits more energy into the target region per treatment than any other laser wavelength. This is also due to the low level of energy loss in the melanin in the epidermis at 589 nm compared to 532 nm.

In other words, yellow light is particularly beneficial in the treatment of vascular lesions such as hemangiomas, spider veins, port-wine stains etc. This is illustrated by the many treatments that have been performed using old yellow light technologies such as Pulse Dye Lasers (PDL) and copper vapour lasers. In fact, the output of the Advalight yellow solid-state laser is comparable to copper vapour lasers and achieves the same excellent results with a similar output of light - now just in a more reliable version with no need for consumables.