WE THOUGHT they were a bid to look cool - but there's another reason for blacked-out glass, too.

And today we can reveal it.

Police say criminals are opting for tinted windows so they won't be seen out and about by officers who would recognise them.

Police in Calderdale have been taking a dim view of people with tinted car windows.

They have been catching motorists who have tinted their windows so darkly they cannot see out of them properly.

Officers say some criminals tint their windows dark so police cannot see them.

Sgt Garry Alderson said: "Some travelling criminals use vehicles with heavily tinted glass so as not to be recognised.

"We want to deny these criminals the use of the road."

And he added that glass tinted dark beyond the legal limit can also cause accidents.

"Glass that is heavily tinted can be a real danger," he said.

"Tinted glass restricts a driver's ability to obtain a clear view of the conditions outside, particularly when it is dark. It is vital a driver can see pedestrians and other vehicles."

He added that other drivers had reduced eye contact with motorists behind tinted windows, which was another danger.

The law applies to the windscreen and the front side windows.

For vehicles registered after April, 1985, the front windscreen must let in at least 75% of light and the side windows 70%.

For vehicles registered before 1985 the figure is 70% for both.

Sgt Alderson added: "Most vehicles these days come with a small amount of tinting as standard, so you don't have to add too much extra for it to become illegal."

He also warned motorists that if they tinted windows too much it may make their insurance invalid.

Police check the windows with a pocket meter.

If the reading comes up as less than 30% police tend to prosecute. If it is 30% to 70% the driver gets the chance to have the tinting removed.

Officers arrested a banned driver on the first day they used the system.

Since then, a further two banned drivers have been arrested and 13 drivers have been reported for summons.

Several uninsured vehicles have also been seized and intelligence gathered about travelling criminals.