Members of my household are preparing for a journey that will involve both regular and light backpacks. Regular hiking backpacks are made to hold a vast amount of gear—you strap them on when you go to the woods for a week or more. They hold food (in a bear-proof canister if you are heading into the wilderness), emergency supplies, clothing, water, sleeping bag, a tarp or tent, cookware and any additional personal supplies. This adds up to a lot of weight, and seasoned backpackers know that they only want to carry one-quarter or so of their body weight on their backs—less if possible.
The light backpacks are different. They don’t have as many cubic inches of packing space and hold only 20–25 pounds of gear. They are made for a different type of trip, for a day hike that requires fewer items.