Cage Free. What exactly does that mean? You might picture hens pecking around a pasture, enjoying plenty of space.

That's what Denver-area mother Cathy Doyle thought "cage-free" means. She raises hens on her family's property and eats the eggs they produce.

"I want to imagine the chickens are roaming around free, happy, rolling around taking dust baths," Doyle said.

Hens who peck in a field or open area and spend significant time outside are considered pasture raised hens, not cage-free hens.

The NOW's investigation shows examples of hens whose eggs are marketed as cage-free live a life where they never see the outdoors and are kept in confined areas with hundreds of other birds.

"Customers absolutely do not know what they're getting when they buy cage free eggs. They think they're getting green pastures and grassy fields. What they're actually getting is huge industrial lots," Wayne Hsiung, of the animal rights group Direct Action Everywhere, said.

The NOW's investigative team followed Hsiung's California group in January as several members sneaked into a large egg farm with cage-free hens to document the conditions. The NOW's crew waited at the property line of the farm as the animal activist recorded video inside.

"The difference between a cage-free and cage facility is they've essentially just taken the walls out but they are still cramming birds into huge industrial sheds where they are lined up shoulder to shoulder," Hsiung said.

Video confirmed by The NOW to have been recorded by the animal rights activists outside of San Francisco showed some birds in distress in the one barn visited.

One bird appeared to have difficulty breathing. Another appeared deceased. Many of the birds appeared to be missing feathers. There appeared to be hundreds of birds in the large barn.

Watch the video above to see conditions inside one farm.

Hsiung said he has seen similar conditions at other cage-free egg farms he has visited previously. Hsiung provided footage of other facilities that he claimed he and members of his group shot this year and last year.

Darrin Karcher is an assistant professor and poultry specialist at Purdue University. He helped build a hen research facility at Michigan State University. Karcher agrees that some people believe cage free means something different than it actually does.

There is no government definition for cage-free eggs, Karcher said, meaning conditions can vary between farms. Some farms adhere to standards required by some industry trade groups.

Karcher says there is no evidence to suggest cage-free hens are happier than hens who live in a cage. Hens living in a cage usually have a dozen birds in a cage.

"From a science standpoint there is nothing that I am aware of that would allow us to say the birds are happier in [a cage-free facility] verses the other," Karcher says.

As a researcher, Karcher says he does not recommend caged or cage free eggs. His goal is to educate the public about methods of raising hens.

The head of United Egg Producers, a trade group representing many egg farmers, declined to answer specific questions about the footage obtained by Direct Action Everywhere. Chad Gregory, President and CEO, United Egg Producers issued a statement:

"United Egg Producers and its farmer-members care about the health and well-being of their flocks and work tirelessly to assure their welfare, as well as the safety and quality of the eggs produced. UEP Certified standards provide science-based, uniform national guidelines for hen health and well-being. For more than 15 years, UEP has had certification standards for hens in traditional housing, and established standards more than a decade ago for hens in cage-free housing. Our members stand behind those standards because they ensure excellent care of hens, while providing options for our customers and consumers."

The farm Direct Action Everywhere investigated but did not return several calls for comment. A spokeswoman with United Egg Producers said she was in contact with the farm and that the farm did not want to comment.

So how do you find eggs from hens that actually spend a lot of time outside? When you go to the grocery store, look for egg cartons that say pasture raised. You can also buy your eggs from a farmer in your area.

If you have a tip about this story or another story idea for The NOW National Investigative Correspondent Jace Larson, email him at jace.larson@scripps.com.