A coolant supply manifold and a coolant discharge manifold are provided on a first end plate of a fuel cell stack. In various embodiments the container includes a slidable button for releasing the lid, the button being contained within a pocket. A drive transistor coupled to the relay coil controls the average voltage across the relay coil responsive to the pulse width modulated signal. The contact plane, the incoming plane and the outgoing plane of the prism are formed such that light transmitting the incoming plane enters the contact plane at an incident angle larger than critical angle and that the light totally reflected by the contact plane goes out through the outgoing plane. The preferred active layers are characterized by a transmittance that is selectively controllable by applying a voltage across the plurality of active layers.