Patent ID: 8203711

Claim:
A light irradiation method of irradiating a specimen moving through a flow channel with directional light, the method comprising: irradiating the specimen with the directional light from a first light source while performing scanning using the directional light in a widthwise direction of the flow channel, the directional light having an at least substantially circular irradiation spot having a diameter that is smaller than a width of the flow channel, obtaining positional information of the specimen prior to irradiating the specimen with the directional light by performing scanning of the specimen with a second irradiation spot from a second light source, and detecting a measurement light that is generated by the irradiation of the specimen by the second light source, wherein irradiating the specimen with the directional light at a given time is based on the obtained positional information of the specimen, and wherein scanning is performed in the widthwise direction of the flow channel at a single position in a flow channel direction a plurality of times during a period of time when the specimen moves through an area irradiated by the irradiation spot.