Introduction: Illumination systems based on sodium and mercury vapor lamps are inefficient and consume a big amount of electrical energy. LED lamps represent an attractive alternative to decrease electricity consumption. On the other hand, photovoltaic systems are being utilized as a renewable energy source to reduce CO2 emissions, but their implementation also depends on economic considerations. Objective: This study aims to demonstrate the technical and economic feasibility of implementing a photovoltaic system to optimize the illumination circuit of a water treatment plant. Methodology: Two possibilities options were considered: off-grid and grid-tied systems. The current illumination circuit was analyzed and the LED equivalent circuit was calculated. Based on the new illumination circuit, a photovoltaic off-grid system was sized to power the LED luminaires during three consecutive days without sunlight. Likewise, a grid-tie system was designed to power the proposed LED illumination circuit. Both scenarios were evaluated by using PVsyst software, which allows establishing parameters for an economic assessment. Results: Although changing luminaires reduces the operating cost by 50 %, the off-grid system is infeasible due to the high initial investment cost, meanwhile the grid-tie system is feasible, with a rate of return that is lower than the one allowed by the company. Conclusions: Changing the current illumination system to LED technology is an economically-wise decision for the company. Regarding the PV grid-tie system, it can be economically attractive if the tax credits and the recent regulation for small-scale generators in Colombia are considered.