An intravascular assembly for catheterization comprising: a. an introducer needle comprising a connection hub and a needle member, wherein the needle member has a lumen, a distal end provided with a blood entry aperture and a proximal end, wherein the connection hub defines an inner chamber, and wherein the proximal end of the needle member is arranged at or within the inner chamber of the connection hub so that blood flowing from the distal end through the lumen of the needle member will exit the proximal end of the needle member and enter or be received by the inner chamber of the connection hub; b. a light guide having a distal end and a proximal end and extending along the lumen of the needle member, wherein the distal end of the light guide is arranged inside the lumen of the needle member and terminates within the distal end of the needle member but is spaced proximally apart from the blood entry aperture at the distal end of the needle member by a distance that is greater than 0.1 mm and smaller than 20 mm; c. an adapter to which the light guide is fixed or mounted, wherein the light guide is arranged to extend through the adapter; and d. at least one light source, wherein the adapter is provided with an interface for a light source, wherein the adapter is connected to the connection hub of the introducer needle, wherein the adapter provides a sealing for the light source from blood in the inner chamber of the connection hub, wherein the adapter is connectable or connected to at least one light source so that light emitted by the light source can enter the light guide or be transmitted into the light guide and be emitted from the distal end of the needle member, and wherein the light emitted from the distal end of the needle member has a total light intensity, and wherein at least 40% of the light emitted from the distal end of the needle member and contributing to the total light intensity has a wavelength between 510 nm and 610 nm. a. an introducer needle comprising a connection hub and a needle member, wherein the needle member has a lumen, a distal end provided with a blood entry aperture and a proximal end, wherein the connection hub defines an inner chamber, and wherein the proximal end of the needle member is arranged at or within the inner chamber of the connection hub so that blood flowing from the distal end through the lumen of the needle member will exit the proximal end of the needle member and enter or be received by the inner chamber of the connection hub; b. a light guide having a distal end and a proximal end and extending along the lumen of the needle member, wherein the distal end of the light guide is arranged inside the lumen of the needle member and terminates within the distal end of the needle member but is spaced proximally apart from the blood entry aperture at the distal end of the needle member by a distance that is greater than 0.1 mm and smaller than 20 mm; c. an adapter to which the light guide is fixed or mounted, wherein the light guide is arranged to extend through the adapter; and d. at least one light source, wherein the adapter is provided with an interface for a light source, wherein the adapter is connected to the connection hub of the introducer needle, wherein the adapter provides a sealing for the light source from blood in the inner chamber of the connection hub, wherein the adapter is connectable or connected to at least one light source so that light emitted by the light source can enter the light guide or be transmitted into the light guide and be emitted from the distal end of the needle member, and wherein the light emitted from the distal end of the needle member has a total light intensity, and wherein at least 40% of the light emitted from the distal end of the needle member and contributing to the total light intensity has a wavelength between 510 nm and 610 nm. wherein the adapter is provided with an interface for a light source, wherein the adapter is connected to the connection hub of the introducer needle, wherein the adapter provides a sealing for the light source from blood in the inner chamber of the connection hub, wherein the adapter is connectable or connected to at least one light source so that light emitted by the light source can enter the light guide or be transmitted into the light guide and be emitted from the distal end of the needle member, and wherein the light emitted from the distal end of the needle member has a total light intensity, and wherein at least 40% of the light emitted from the distal end of the needle member and contributing to the total light intensity has a wavelength between 510 nm and 610 nm.