Low-E window film is made of materials which are low-emissivity, which means that they block UV light from the sun. UV light can damage your furnishings, but more importantly, it can run up your air conditioning bills in the summer.
The film can reflect heat or deflect heat. For this reason, it is best to place it on the inside of the window in the winter months to preserve heat, but place it on the outside of the window in summer to keep heat out. There are different tints available. Tints are the layer of thickness of the metallic covering. It can vary which allows you to decide how much light you want to let in.
More energy efficient glasses block natural light. Adding tint blocks light, reduces glare and some heat, but conducts heat and cold. Insulated glass, however, does not protect from direct sunlight. You can coat the glass surface using Low-E. The coating is thin and reflects UV light.