Yes, the LED being dim is normal. All the current goes through the LED as it's in series with the output. That way, if the LED is lit at all, you know for sure that something is actually conducting through the water. But the low 1 milliamp current doesn't light up an LED very much because they are made to handle up to 20 milliamps. If the water is very pure, the LED may be quite dim for several minutes...even many minutes.