You use them to bias the amp. If the lights are on, that means the bias is set too high. There should be something you can turn with a small flathead screwdriver near each of the lights. Turn the screws counter clockwise slowly until the light goes out. You want to be right at the point where the light goes out, and no further. You should really do this right away, because if the bias is set too high, you may damage the tubes.
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