1. Introduction

Several elements contribute to the aging process of LED bulbs, such as ambient temperature, relative humidity, and the levels of electrical current and voltage applied. Higher temperatures tend to speed up the aging mechanism, whereas environmental humidity leads to a slower but continuous decline in performance [1-3]. For the purpose of this study, all measurements were conducted under controlled conditions set at 25 ± 1 °C with a humidity level of 50%. Operating the LED chip beyond its recommended current and voltage limits introduces electrical stress, which in turn causes early deterioration. LED technology is commonly employed for indoor illumination applications. The current study evaluates several electrical, light-related (photometric), and selected radiation-based (radiometric) characteristics of LED lamps. Since these lamps consist of multiple internal components, various types of energy losses may occur within them [4-6].

1.1. Driver electronics

An LED driver is an electrical device that regulates power to an LED or a string of LEDs. It is a crucial piece of an LED circuit, and to operate without one will result in system failure. LED drivers convert AC to DC and subsequently supply a constant. All LED lights need an LED driver to convert the mains power supply, which provides a much higher voltage than the constant direct current of 12V or 24V that LEDs require, into a more suitable one. This helps to prevent burnout and can lower the risk of fire. [7-9].

1.2. Optics

Under standard operating conditions, LEDs typically emit light across a viewing angle of approximately 120 degrees. For applications that demand a more concentrated beam, a secondary optical element is often placed directly over the LED. This component directs the light internally to produce various beam shapes, including spot, medium spot, wide spot, or elliptical spot patterns. As a result, most commercial LED lamps incorporate secondary optics such as lenses, reflectors, or total internal reflection (TIR) optics. These elements are designed to capture nearly all the light emitted by the LED and enhance its luminous intensity. Among the available options, the convex lens positioned around the LED remains the most commonly used type. Nevertheless, ongoing technological advancements have led to the growing popularity of other lens varieties as well.

In addition to optical components, the performance of an LED lamp depends heavily on its driver electronics, also referred to as the power supply unit. This component is responsible for converting the standard mains voltage into the specific operating voltage required by the LED. The internal design of these electronic circuits varies from one manufacturer to another, and their energy conversion efficiency typically ranges between 70% and 90% [13, 14].

1.3. Power factor

The concept of power factor applies specifically to alternating current (AC) electrical systems. Its value always falls between 0 and 1.0, with higher numbers indicating a better or more efficient power factor. The importance of the power factor stems from the fact that utility companies supply customers with volt-amperes, yet calculate their bills based on watts. The mathematical relationship is expressed as watts equals volts multiplied by amperes multiplied by the power factor (P = V × I × PF). Consequently, any power factor below 1.0 forces the utility to generate more volt-amperes than the theoretical minimum required to deliver the actual power measured in watts. This excess generation leads to increased costs in both electricity production and transmission. A power factor above 0.85 or 85% is generally considered acceptable. Utility providers often impose financial penalties on customers whose overall building electrical systems fail to maintain a power factor at or above this threshold [15-17]. 

2. Experimental

2.1. Aging cycles

The lamp aging process was conducted under stable environmental conditions within a specialized laboratory facility. The temperature inside the aging area was maintained at 25 ± 1°C. The lamps were mounted on a wall and operated in their designated orientation, with the light directed downward. Each lamp was connected to a power supply located inside an integrating sphere. The switching process—both turning the lamps on and off—was performed manually. For all lamp groups tested, a duty cycle consisting of 11 hours of continuous operation followed by 1 hour off was applied throughout the aging procedure.

2.2. Integrating sphere-based method for Luminous flux measurement

Figure 2 shows that the integrating sphere is hollow, with its interior coated with a very stable, diffuse-reflecting material, demonstrating that it is suitable for carrying out measurements of luminous flux. The sphere has a port for the LED lamp and a baffled port for the detector. The integrating sphere consists of a cosine-corrected photometer equipped with a V(λ) filter from the LMT company. The detector has a linear response with a range of 16–28 nA/lx, based on these characteristics, the total luminous flux of tested lamps can be measured in direct substitution with that of standard lamps. The sphere wall is coated with barium sulfate paint, which has a diffuse reflectance of approximately 97% in the visible region. The integrating sphere was also equipped with a tungsten auxiliary lamp (100 W) on the sphere wall to measure the self-absorption effects of the lamp in the sphere. The room temperature of the photometry laboratory was controlled to be about 24 °C. A temperature sensor is mounted to measure the air temperature inside the sphere. During lamp operation, the ambient temperature in the sphere was approximately 25 °C.

2.3. AC power supply for electrical parameters

Figure 3 shows an Agilent AC power supply used to measure the electrical parameters.  

2.4. The UV radiometer

A UV radiometer is a precision instrument used to measure the intensity of ultraviolet (UV) radiation across specific wavelength bands (UVA, UVB, or UVC).

2.4.1. Key features

• Sensor probe with photodiodes and optical filters to detect targeted UV wavelengths.

• Digital display showing readings in mW/cm², W/m², or UV Index

• High accuracy with built-in calibration and minimal interference from visible light

2.4.2. Main uses

• Monitoring UV curing in industrial printing and coatings

• Testing UVC sterilizers and medical phototherapy devices

• Measuring solar UV radiation for environmental and agricultural studies

• Ensuring workplace safety by assessing UV exposure risks

3. Results and discussion

Figures 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 show the variation of flux, power, current, and power factor for three types of lamps.

As shown in Figures 5 to 7 for the 9-watt lamps, the E1 lamp had the highest flux, while the T1 lamp had the highest wattage and V1 the lowest. The current E1 was the highest, while T1 was the lowest and V1 was in between. The power factor of T1 was higher than that of E1 and V1. In Figures 8 to 11 for the 12-watt lamps, E4 and V4 had the same or higher flux than that of T4. The wattage of T4 was the highest, V4 the lowest, and E4 moderate. The current E4 is the highest, T4 the lowest, and V4 intermediate. The power factor of T4 is higher than that of E4 and V4.

Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding

No funding was received for writing this manuscript.