From Lexicanum

Photon grenades are designed to emit an extremely bright pulse of multi-spectrum light which will damage any viewing equipment or optical devices. This will blind them and make them effectively put them into a protracted state of shock, during which time they cannot defend themselves.^1-p92

Tau photon grenades are designed to emit a sonic blast and a pulse of multi-spectrum light. They can be thrown by hand or fired from a Pulse Carbine.²

Sources

• ¹:Warhammer 40,000: Rogue Trader
• ²:Warhammer 40,000: Wargear

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