The FDA has given the following definition of the light food claim:
for foods deriving more than 50 percent of calories from fat, the light product is reduced in fat by at least 50 percent;
For foods having less than 50 percent of the calories from fat, the “light product” designation is either reduced in calories by at least one-third or reduced in fat by at least 50 percent;
For foods with modified sodium content, the “light product” description must have a reduction in sodium by at least 50 percent.
Light food products must show a reduction as compared to a reference food, which is basically the average product in that category. The most common example I’ve seen is for the manufacturer to use an average of the three top-national or regional brands of a given product. It has to be a similar product where the only difference is a result of reformulation. If the reference food already is considered low in the designated nutrient, the light food claim cannot be used.
“Light” also may be used to describe certain physical attributes of a food, such as the texture or the color. However, if the light food description is used in this manner as a description, the product’s label must state that “light” refers to that particular product attribute (for example, “light in color” or “light in texture”).
This definition does little to help us understand exactly what the producer did to create a product that is “light” compared to the competition. Did they use leaner products meaning less fat? Did they refrain from adding large amounts of sodium? That would be great, but it is not guaranteed. They can also replace natural sugar or butter with artificial sweeteners to reduce calories and fat. That doesn’t necessarily make it any healthier for you as many additives contain dangerous chemicals.