Apparatus and method for irradiating a surface with light

A method for irradiating multiple portions of a scalp surface with light, the method comprising:

• providing an optical element comprising a substantially optically transmissive and substantially thermally conductive material, the optical element having a first surface and a second surface;
• placing the first surface in thermal communication with the scalp surface;
• propagating the light along a first optical path through the second surface and through the first surface to a first area of the scalp surface;
• propagating the light along the first optical path through the second surface and through the first surface to a second area of the scalp surface,
• wherein the first and second areas of the scalp surface are each at least 1 cm2 and are spaced apart from each other on the scalp surface,
• wherein the light propagated to at least the first and second areas of the scalp surface is transmitted through intervening tissue to irradiate at least first and second areas of the patient's brain that overlap each other, and wherein a time-averaged power density of the light at the scalp surface is between about 10 mW/cm2 to about 10 W/cm2;
• detecting, using a sensor that is in signal communication with a logic circuit, radiation propagating along a second optical path from at least a portion of the second surface, the first optical path and the second optical path having a non-zero angle therebetween;
• and
• adjusting, by the logic circuit and responsive to the signal communication received from the sensor, one or more parameters of the propagating light.