By "horse arena" I assume you are talking an area for either excercising, competetive events, training, etc. The horses are typically only in these areas for limited time and are not actually housed there. In my opinion this is not a Art 547 area, so nothing in that section would apply - if that is what you are after. It is a general purpose area unless some other condition changes that.
If it is an arena with enough spectator area it is probably a Place of assembly occupancy - with possible 547 areas outside the arena area.
There are some rather large barns here that have indoor arenas. That might change the requirements if that's what the OP has.
547.1 Scope.
The provisions of this article shall apply to the following agricultural buildings or that part of a building or adjacent areas of similar or like nature as specified in 547.1(A) and (B).
(A) Excessive Dust and Dust with Water. Agricultural buildings where excessive dust and dust with water may accumulate, including all areas of poultry, livestock, and fish confinement systems, where litter dust or feed dust, including mineral feed particles, may accumulate.
(B) Corrosive Atmosphere. Agricultural buildings where a corrosive atmosphere exists. Such buildings include areas where the following conditions exist:
(1) Poultry and animal excrement may cause corrosive vapors.
(2) Corrosive particles may combine with water.
(3) The area is damp and wet by reason of periodic washing for cleaning and sanitizing with water and cleansing agents.
(4) Similar conditions exist.
If 547 is what is being questioned start with 547.1.
My experience the area called the "Arena" is not nearly as severe when it comes to corrosive conditions, or even dust or water.
They have rodeos and other shows with livestock in huge civic centers. Not exactly the same, but not all that different either. The arena is a show area and the animals are not there long enough to create the conditions 547 is concerned about.
Call me too lazy to look - but what section could conceivably require an enclosed lens?
547.5 doesn't apply to luminaires. Do you mean 547.8(A)?
Call me too lazy to look - but what section could conceivably require an enclosed lens?
Big issue may be any possibility of broken glass falling onto the dirt. It can badly injure or ruin a hoof.
A new to me customer has 6 - lamp T5 HO fixtures in his riding arena. No guard, no lens. The horses are not stabled in this building. Better lit than some of the school gyms I have been in.
Some of these horses may be very high paid athletes that require high quality lighting.
Good call, but I don't think the Code would give a hoof about that.:lol: