As the typical modern car can run its headlights without depleting the battery, why the reluctance to light up? If visibility deteriorates for any reason – not just darkness, but familiar grey drizzle – you shouldn’t hesitate to put your dipped headlights on. A good rule of thumb is to make a point of turning on your headlights whenever you need to use your windscreen wipers.
You may feel you can see well enough, so why bother? But what you can see is not the whole story: you should aim to see and be seen. Other road users may not have eyesight as good as yours. And in gloomy conditions, you need to look particularly carefully in your mirrors before changing lanes. It may be that the driver who hasn’t ‘lit up’ is attempting to overtake you.