Doorbell white LED

When I bought my device I ran it on battery power till I was able to get constant power to the device. When I first used the device and the device was waiting for a ring, it was dark - no LED. When I connected it to power the ring button was surounder by dim constant white lit LED. After a while that white LED no longer is lit. Is that a setting or is that a failure of the device. If it is a setting, I have been unable to find anywhere to restore it to be lit constatntly.Looking for some info