Option 1 states that a light year is a unit for measuring very large distances. This statement is correct. A light year is defined as the distance that light travels in one year in a vacuum. Since light travels at a constant speed of approximately 300,000 kilometers per second, a light year is a very large distance, measuring about 9.46 trillion kilometers.

Option 2 states that a light year is a unit for measuring very large time intervals. This statement is incorrect. A light year is used to measure distances, not time intervals. It represents the distance that light travels in one year, not the time it takes for light to travel that distance.

Option 3 states that a light year is a unit for measuring the intensity of light. This statement is incorrect. A light-year is a measure of distance, not intensity. Intensity of light is usually measured in terms of watts per square meter or other appropriate units.

Since only statement 1 is correct, the correct answer is option 4.