After 150 years of sparking ignition in internal combustion engines, spark plugs may someday be replaced by laser igniters, Japanese researchers say.

A switch to laser igniters would yield cleaner, more efficient and more economical vehicles, they say.

Previously, lasers strong enough to spark the ignition of air-fuel mixtures in an engine were much too bulky to fit under a car's hood, but Japanese researchers say they've developed the first laser system small enough to screw into an engine's cylinder head.

Their finding will be presented at the Conference on Laser and Electro Optics to be held in Baltimore in May, a release from the Optical Society of America said Wednesday.

Takunori Taira of Japan's National Institutes of Natural Sciences, one of the presentation's authors, says the new laser system is made from ceramics and could be produced inexpensively in large volumes.

The lasers promise less pollution and greater fuel efficiency because they will allow engines to run cleaner, burning more air and less fuel, the researchers say.

This would create less nitrogen oxide emissions, a component of smog, they say.