Gardaí are calling on drivers to check their lights to avoid a possible minimum fine of €60.
The force regularly sets up specific operations with mounted checkpoints checking lights on vehicles.
Motorists are usually given warnings and asked to fix lights or handed out on-the-spot fines for broken bulbs.
Some 550,000 cars, or 20% of all cars on Irish roads, fail the NCT every year for defective lighting, according to the Road Safety Authority (RSA).
Vehicles with only one headlight or tail light are regularly seen on roads.
If a light is defective, the driver's range of vision is severely compromised and others may find it difficult to see you.
A vehicle with one headlight could easily be mistaken for a motorcycle and an oncoming car may not allow the necessary space on a road.
It would also be difficult to see a pedestrian out walking because of lack of illumination.
Fog lights should also be used appropriately as they can dazzle and distract other drivers and easily cause a collision.
Fog lights must only be used in fog, falling snow or during heavy rain.
Some motorists incorrectly use them to compensate when a dipped headlight beam is broken.