In homes, the dimming of lighting can be attributed to power draws. It's momentarily, but if a large appliance requires power, the other appliances on the circuit may dim.
the circuits of all lights along with the major appliances ( Refgiretor, washing machine, T. v. , )cicuits may cause the problem. please check with electrician. otherwise some problem in transformer
Consumption of power can cause dimming of electrical lights. Either from your home or a large drain on electrical grid. If it happens constantly you might need an electrical upgrade.