Riding in school buses in the early morning, then sitting in poorly lighted classrooms are the main reasons students have trouble getting to sleep at night, according to new research. Teenagers, like everyone else, need bright lights in the morning, particularly in the blue wavelengths, to synchronize their inner, circadian rhythms  the body’s natural sleep and waking cycle  with nature’s cycles of day and night.

If they are deprived of blue light during the morning, they go to sleep an average of six minutes later each night, until their bodies are completely out of synch with the school day, researchers from Rensselaer Polytechnic Institute reported Tuesday in the journal Neuroendocrinology Letters.

The finding was made by fitting a group of students with goggles that blocked blue light and discovering that their circadian rhythms were significantly affected. “These morning-light- deprived teenagers are going to bed later, getting less sleep and possibly underperforming on standardized tests,” said lead author Mariana Figueiro, a sleep researcher at RPI’s Lighting Research Center. “We are starting to call this the ‘teenage night owl syndrome.’ ”

Incandescent lights should never be used in classrooms because “they are heavy on yellow and red, and the circadian system is not tuned to those colors,” Figueiro said. “You want incandescent light sources in the evening.”

Some fluorescent lights are also not very good. Most that are currently used produce orange or reddish light, but it is now possible to purchase bulbs that emit more blue.

More than 25% of U.S. children have chronic health problems

More than one-quarter of all U.S. children have a chronic health condition, new research suggests, a significant increase over the rate seen in an earlier decade.

But the report in the Journal of the American Medical Association doesn’t suggest that kids are less healthy than they used to be.

The comprehensive look at children from 1988 through 2006 also revealed that health conditions themselves have changed. Fewer children today are affected by congenital defects, infectious diseases and accidents than they were 50 years ago; instead, cultural, lifestyle and environmental conditions appear to be the root cause of many pediatric illnesses.

And many behavioral and mental health conditions, such as attention deficit disorder, weren’t diagnosed decades ago.

Researchers analyzed the prevalence of illnesses by surveying the mothers of approximately 5,000 children. Data from three time periods were analyzed: 1988 to 1994, 1994 to 2000 and 2000 to 2006.

In the analysis, researchers found that the rate of chronic health conditions increased from 12.8 percent in 1994 to 26.6 percent in 2006.

Hispanic and black youths and males were more likely to have health problems.