why are outdoor swimming pool and garden lighting fixtures primarily powered by alternating current (AC)?

Outdoor swimming pool and garden lighting fixtures are mainly powered by low-voltage alternating current (AC), usually 12V AC, and are supplied through isolation transformers.
This is mainly done for several considerations such as safety, durability, practicality and compliance with regulations.

1. Safety is of Paramount importance in a humid environment

According to the outdoor lighting installation regulations in IEC 60598-2-18, low-voltage systems with contact voltages limited to ≤15V AC RMS (or ≤30V DC) are permitted to minimize the risk of electric shock in areas in contact with water.The AC system uses a dedicated isolation transformer for swimming pools, which can prevent high voltage (such as 120V) from leaking to the low voltage side in case of a fault. Dc power supplies (such as switching power supplies) do not always have this function, or their implementation reliability is also relatively low. For garden lighting, similar low-voltage AC devices can reduce the dangers brought by rain or irrigation and comply with general outdoor electrical standards.

2. Over time, low-voltage alternating current can reduce electrolytic corrosion.

In damp or submerged environments, direct current (DC) accelerates corrosion through unidirectional electron flow, leading to continuous ion migration and metal degradation at the anode. Alternating current (AC) generates a net-zero effect by periodically changing direction, thereby offsetting most of such damage and extending the lifespan of lamps in swimming pools (where the chemical composition of water quality can exacerbate the problem) and gardens (where they are exposed to soil moisture and weather).

3. Simplicity, cost and Compatibility

Ac transformers are low in price, easy to produce, and require simpler wiring, usually only two or three wires, including grounding wires. Therefore, it is very convenient to install in both swimming pools and gardens. They can be well integrated with built-in controllers for dimming or color changes, and most traditional lamps (especially incandescent lamps or early LED lamps) are designed for alternating current. Although direct current can make modern LED lights more efficient by avoiding conversion losses, it usually requires more complex Settings (for example, RGB control needs a separate circuit), and it is not always interchangeable. If not matched properly, it can cause operational problems.

Although some modern LED lighting systems use direct current for energy conservation or to achieve off-grid compatibility (such as solar power supply), due to the above-mentioned advantages of alternating current and the need to be equipped with appropriate leakage protection devices (GFCI) and equipotential bonding on the main side to enhance safety, alternating current remains the industry standard for outdoor applications powered by mains electricity.