Lambda max is the wavelength at which the maximum fraction of light is absorbed by a solution. Lambda (?) is a Greek letter that scientists use as the symbol for wavelength.
Color and Energy
The absorbance of light gives solutions their color. The color and energy of light can be determined from its wavelength.
Light is Absorbed by Electrons
Electrons in atoms and molecules move around the nucleus in regions called orbitals or energy levels. An electron can move up to the next level if it is given the exact amount of energy required to be in the next level. Light can provide that energy.
When light is shone on a solution, some of the energy of light absorbed is affected by and transferred to the solvent. The light absorbance is spread out around a central maximum wavelength--lambda max.
Local Lambda Max
There is usually more than one absorbance peak for a substance. Each local absorbance peak may be referred to as a local maximum.
Lambda Max in the UV
Most solutions also do absorb, or solely absorb, ultraviolet (UV) light. The wavelengths most strongly absorbed typically occur in the UV. Often people refer to absorbance peaks of visible light as lambda max even when a stronger peak may occur in the UV region.