The warm-up period of LEDs is essential for determining accurate values ​​for parameters such as luminous flux, color temperature, and power consumption. This period affects the reliability and accuracy of measurements, as LEDs undergo changes that affect their performance characteristics. Accurate measurements during the warm-up phase are essential to avoid suboptimal usage, increased energy consumption, reduced lamp life, and variations in lighting quality. Our study measures the stability of LEDs over time for three categories of white LEDs (9, 12, and 15 W) from different lighting companies in the Egyptian market. We present detailed experimental data on electrical parameters (such as power factor and current) and optical parameters (such as luminous flux). By studying these parameters over time, we evaluate the performance of each type of lamp under typical operating conditions and identify variations in stability. The results highlight the importance of considering set-up time and settling when selecting LEDs for specific applications. Set-up times and performance characteristics vary between lamps, greatly impacting their suitability for specific environments and uses. Careful evaluation ensures optimal performance and reliability for residential, commercial, or industrial applications. This study provides valuable insights for consumers and manufacturers, helping them select and design LED lighting solutions that meet specific needs and performance criteria. Understanding the set-up behavior of LEDs contributes to more informed decisions, which improves energy efficiency and lighting quality.