You have to see the specks on the LED light. All tested bulbs have a graph with spread on height. Lets say your light replacement is 14 feet tall you cross the 14 feet to spread. I hope this helps but I do it all the time. Some High Presser Sodium will have a spread of 20 feet wide at 14 feet up.
Have you looked how much light you need in the backyard and where you need the light? Often a one for one replacement is a gross overkill. You may be able to significantly reduce the size (lumen equivalent) of the light. Also are you in rural or urban area... if an urban area with neighbors close by you may want to choose a light that keeps more of the light on your back yard....
Well said Dennis, try a lighting calculation for the space you need.
What is the purpose of lighting the backyard ? Sense of safety, night time enjoyment of the garden, some help seeing the path, to walk from garage to home ? Each of these purposes will lead to a different design. of fixtures, fixture placement and light source quality and output. Are you installing a 300 watt LED flood with the present efficacy of LED bulbs of close to 100 lumens per watt, that is a 30,000 lumens point source, that is a very bright light concentrated from a very small (surface area) source. Tell us more about what you want to accomplish, then the different solutions can be developed .
Greetings Jan Gravemaker.