Is too much screen time bad for kids?

You check in to say good night to your son only to find he is playing "Fortnite" in bed. Or your daughter is busy texting when she is supposed to be studying. Children and their phones are inseparable today, and all that reading and playing games on their handheld devices may be harming their vision.

To reduce screen time, some parents ban phones at the dinner table. This applies to both adults and children. And in some homes, playing games or texting must stop two hours before bedtime. To put a hard stop on screen time, some moms and dads set time limits on their children's daily device use.

For example, when a total of two hours of screen time has been reached, no more texting, game playing or YouTube watching.

According to The Vision Council, 72 percent of American parents report their children routinely engage in more than two hours of screen time per day. And it's very likely most kids actually spend significantly more time staring at screens than their parents think they do.

As kids grow, their screen time tends to grow with them. And even very young children these days are spending a significant amount of time each day staring at screens. According to Common Sense Media, young children in the U.S. spend the following amount of time each day using digital devices:

• Kids under 2 years of age: 42 minutes per day
• Kids ages 2 to 4: 2.5 hours per day
• Children ages 5 to 8: nearly 3 hours per day

The Vision Council says 30 percent of parents report their children experience at least one of the following symptoms after being exposed to more than two hours of screen time per day:

• Headaches
• Neck/shoulder pain
• Eye strain, dry or irritated eyes
• Reduced attention span
• Poor behavior
• Irritability

Any of these symptoms could potentially affect academic performance and social interactions. The rapid rise of myopia, or nearsightedness, worldwide has been linked to increased use of and exposure to electronic devices. In Singapore, for example, 65 percent of students in Primary 6 are myopic.

In the United States and Europe, where myopia rates traditionally have been lower, around half of young adults now suffer from myopia compared with 25 percent in the 1970s.

The LED screens of computers and portable digital devices emit a broad spectrum of visible light. Most of these light rays are harmless, but a portion of the light emitted by these screens is relatively high-energy visible light called "blue light." Blue light has shorter wavelengths and higher energy than other visible light rays. And laboratory research suggests certain bands of blue light may be harmful to the light-sensitive retina of the eye over time.

Blue light also plays an important role in regulating our body's circadian rhythm. This basically is an internal clock that's running in our brain and cycles between alertness and sleepiness at regular intervals over a 24-hour period. It's also called our sleep/wake cycle. Too much exposure to blue light at the wrong time of day can disrupt a person's normal sleep/wake cycle, which can have serious health consequences.

When talking about the risks of too much screen time for kids, we’re basically talking about the potential harmful effects of too much blue light. And while it's true that staring at the screens of digital devices adds to the amount of blue light exposure kids get over the course of their lifetime, it's important to point out that the sun emits far more harmful blue light than computers, e-tablets and smartphones.

So the blue light exposure from digital devices is an added exposure, over and above the larger amount of blue light exposure a person gets from sunlight. A second important factor to consider is the timing of the exposure. Blue light exposure from the sun only occurs from sunup to sundown. But blue light exposure from screen time can occur at any hour of the day, including well into the night. Possible risks from too much screen time for kids can be categorized as immediate or long-term.