Abstract: The present invention relates to an improved technology for a device that identifies and diagnoses an environmental stress state of plants. An environmental stress diagnosis device comprises a measurement light source 12, an induction light source 14, and a transmitted light detector 18. The measurement light source 12 radiates a first measurement light ML1 and a second measurement light ML2 to a plant sample S, the induction light source 14 radiates a first photosynthesis inducing light FR and a second photosynthesis inducing light AL to the plant sample S, and the transmitted light detector 18 detects a first transmitted light TL1 and a second transmitted light TL2. The control unit 20 has an analysis circuit 20a and a control circuit 20b.

Abstract: The present invention relates to an improved technology for a device that identifies and diagnoses an environmental stress state of plants. A control circuit 20b controls a measurement light source 12 such that a second measurement light ML2 has higher power than a first measurement light ML1 and the first measurement light ML1 and the second measurement light ML2 become opposite-phase rectangular waves, and further controls the measurement light source 12 such that the first measurement light ML1 and the second measurement light ML2 are output in synchronization to form the first measurement light ML1 and the second measurement light ML2 into a quasi-single composite rectangular wave measurement light ML3 of 5 kHz to 30 kHz. A transmitted light detector 18 detects the composite rectangular wave measurement light ML3 transmitted through a plant sample S as a composite rectangular wave transmitted light TL.