Whenever Malcolm Brown, 22, of West Donegal Township, drives home from Drexel University at night, he encounters the same dazzling lights.

They peep in and out of the slots in median guardrails. They roll their little bluish-white eyes along the tops of cement barriers. They sneak up behind him and bounce off his rearview mirror, making him wince.

His twin brother, Taylor Brown, has encountered them, too.

They are high-intensity discharge headlights, or HIDs, which have grown in popularity in the past several years.

Manufacturers say they are safer than traditional headlights because they illuminate the road better and expand peripheral vision.

Many motorists sharing the road with vehicles using HIDs, however, are less positive about them.

"I hate them!" the twins said in unison Friday at Central Market.

"I just don't like when they come up behind you," Taylor said. "It looks like high beams, and the blue light is very distracting."

"Plus, they flicker a lot, and it affects how you see anything," Malcolm said.

Blinding HIDs on approaching cars prevent Taylor from seeing the road, deer, or pedestrians, he said.

There are four types of headlights, each with a different light source: tungsten (filament); halogen (halogen gas); HID (xenon gas); and LED (silicon computer chips).

Each varies in color and brightness. Halogen lights appear yellow and illuminate at 2,800 degrees Kelvin. HIDs emit bluish-white light at 4,500 degrees Kelvin.

And LEDs shine white light at a whopping 6,000 degrees Kelvin. That's brighter than sunlight, which is 5,600 degrees Kelvin.

LED headlights are few because they are relatively new, appearing mostly in luxury and performance vehicles.

Most vehicles on the road have halogen bulbs.

But use of HID headlights is on the rise.

According to the Motor Vehicle Lighting Council — a coalition of automotive lighting manufacturers — HIDs were introduced in the 1990s in luxury and performance cars in Europe and Japan.

They are now available, factory-installed, in at least 95 vehicle models in North America and a growing number of motorists are installing them in older vehicles.

"AutoZone continues to see an increase in premium lighting sales," Brenda E. Berry, corporate spokeswoman for AutoZone wrote in an e-mail.

 "Our customers are installing these lights primarily for safety purposes; the lights allow drivers to see further and brake faster."

They also last longer. HIDs perform for 3,000 hours, whereas halogens last about 1,000 hours, according to the Motor Vehicle Lighting Council.

"HIDs are popular," Keith Diehl, who installs them at Custom Hot Whips in Lancaster said. "They provide a lot of light and consume a lot less power than halogen."

But all that light isn't always welcome.

According to the most recent study —done at University of Kansas Medical Center and published in the British Journal of Ophthalmology in 2003 —complaints are justified.

It found that HIDs cause glare, diminishing drivers' ability to see roadway and pedestrians.

The Motor Vehicle Lighting Council counters that claim.

"Additional light output is designed to produce wider beam patterns with a more even distribution of light, providing drivers with better peripheral vision and maximum seeing distance," it says in a fact sheet posted on its Web site, mvlc.info.

But the University of Kansas study contends that "the increased light projected by HID headlights is potentially valuable, but serious questions remain regarding how and where it should be projected,"

Diehl stressed that HIDs must be properly installed and aimed correctly.

"HIDs point toward the ground," he said.

That should reduce any glare on oncoming motorists, Diehl said.

On the other hand, he said, "If you're in a lower car and you've got an SUV right behind you, you're going to have them aimed right at you," in the rear-view mirror.

As for the industry's claimed peripheral-vision improvement, drivers who replace their vehicles' halogens with HIDs typically don't get that benefit because they don't replace the stock light housing along with the bulb, Diehl said.

Experience may overshadow industry claims for drivers disturbed by the brilliance and bluish-white color of HID headlights.

"It's bad because it takes your eyes away from the road," Malcolm said.

Yet the growing trend toward HID headlights could mean they are here to stay.