Fundamental Technical Standards

The investigation is anchored on a solid normative basis, composed of regulations and technical procedures that ensure the comparability and reproducibility of results. The following applied standards stand out:

These standards ensure that the tests conducted at LABLUX/UFF comply with national and international performance and safety requirements. They also underpin the criteria for mandatory certification of products in Brazil.

Degradation of Optical Components

Although LED chips exhibit good stability over the projected lifespan (50,000 hours or more), several studies indicate that the optical elements of luminaires - such as diffusers and collimating lenses made of polycarbonate or polypropylene - are sensitive to degradation induced by ultraviolet radiation and thermal variations ([5], [6]). Phenomena such as yellowing, loss of transparency, formation of microcracks, and modification of the refractive index result in significant losses of useful luminous flux, alteration of the emission spectrum, and distortion of the spatial distribution of light. Figure 1 illustrates the outcome of this process in lenses exposed for six thousand hours in a UV chamber.

Figure 1: Process in Lenses Exposed for Six Thousand Hours in a UV Chamber. 

Importance of Systemic Evaluation

The photometric behavior of an LED luminaire cannot be evaluated in isolation from the emitting source. The interaction between the various elements - light source, driver, housing, heat sink, optical elements, and mounting system - determines the actual performance of the luminaire in the field ([4], [5]). Thus, tests such as absolute photometry, ISTMT (In Situ Temperature Measurement Test), and accelerated aging simulations are essential to extrapolate the LED behavior in the laboratory to real urban operating conditions. The use of the TM-21/LM-80 spreadsheet, as recommended by Energy Star [4], enables this projection based on reliable measurements.

Luminaire Models

The following LED luminaire models were analyzed as shown in Table 1, with typical application in public lighting:

Table 1: LED Luminaire Models 

The selection of models was based on availability at the LABLUX/UFF laboratory and the representativeness of the national market. All models were provided by manufacturers with a consolidated presence in the public lighting segment.

Methodological Considerations

The luminaires used were made available exclusively for testing purposes, with mandatory return to the manufacturer at the end of the study, according to the granting protocol.

The 200W luminaire (GL 421) was the only one to have the LM-80 report of the LED, allowing the In Situ Test (ISTMT) to be conducted with an estimated lifespan based on TM- 21 extrapolation. The other luminaires were subjected to flux maintenance tests, according to the guidelines of [9].

All experimental tests were conducted on fully assembled luminaires, evaluated as integrated systems. The in-situ measurement was the only test performed at the LED level; however, it was carried out with the LED mounted within the luminaire assembly, ensuring that the electrical, thermal, and optical operating conditions were representative of actual luminaire operation.

All tests were conducted at the LABLUX laboratory, and the reported results present traceable measurement uncertainty values.

Equipment Used

The following instruments were used (Figure 2), all properly calibrated according to metrological requirements:

Figure 2: Ulbricht Integrating Sphere and Goniophotometer 

All tests were conducted in a controlled environment (25 ± 1 ºC and relative humidity < 65%).

Testing Schedule

The luminaires remained in continuous operation for six thousand hours, with data collection at regular intervals. Table 2 summarizes the adopted schedule:

Table 2: Summary of the schedule 

Photometric Test

The photometric tests were conducted according to the parameters of IES LM-79-19 and INMETRO Ordinance No. 25/2022. Measurements were taken initially and after intervals of 1000h, 2000h, 3000h, and 6000h. The following parameters were recorded:

Goniometric Test

The goniometric test was conducted using a type C goniophotometer, according to the IES LM-79-19 specification. The equipment allows measuring the spatial distribution of luminous intensity in spherical coordinates and generating photometric files (.IES). Variations of the BUG (Backlight, Uplight, Glare) system were evaluated over the initial 3000h of operation. The 80W and 150W luminaires showed variations in the glare index and in the flow distribution, changing from B2-U2-G2 to B3-U2-G2 and B3-U1-G1 respectively. The 200W luminaire showed stability in the BUG parameter, maintaining the classification B4-U2- G4.

Ultraviolet Test (UV)

The UV test was conducted in the OTS UV Test Machine chamber, illustrated in Figure 3, simulating continuous solar exposure with UV-B radiation (280-315 nm) and control of temperature and humidity.

Figure 3: Temperature Trend Line of the Studied Models 

The polypropylene lenses remained in the chamber for 2016h, in cycles of 12h, with 8h exposed to 70 ºC and 0.49 W/m², and 4h with humidity at 100% at 50 ºC. Cloudiness, loss of transparency, and color change were observed in the lenses.

Life Test

The luminaires were kept in continuous operation for six thousand hours in a controlled environment as illustrated in Figure 4. This test, according to [3], allows verifying the maintenance of luminous flux and other characteristics over time. The measurements followed the same periodicity as the photometric tests.

Figure 4: Life Test 

In Situ Thermal Test (ISTMT)

The ISTMT test was applied exclusively to the 200W GL 421 luminaire, which had an LM-80 report provided by the manufacturer. According to IES TM-21-11 and Energy Star [4], the LED temperature was measured using a type K thermocouple, installed at the point of highest thermal dissipation, as shown in Figure 5.

Figure 5: Connections in the Luminaire for the ISTMT Test 

During the tests, the luminaire was positioned in the climate chamber at 45 ºC for 40 minutes as illustrated in Figure 6. The temperature and current data allowed for a comparison of performance with the limits of LM-80.

Maintenance of Luminous Flux

The depreciation of luminous flux was evaluated through photometric measurements conducted at multiple time intervals over six thousand hours of operation. The results indicate that luminous flux loss becomes more pronounced after three thousand hours, with the most significant degradation observed in the 150W and 200W luminaires. The 150W model exhibited an approximate luminous flux reduction of 25% at 6000 h, suggesting potential non-compliance with the maintenance criteria established by INMETRO Ordinance No. 25/2022.

The distinct luminous flux behaviors observed between the 150W and 80W luminaires are attributed to differences in thermal and optical stress associated with their respective operating power levels. Higher-power luminaires are subjected to increased thermal load, elevated LED junction temperatures, and higher photon density, which accelerate degradation mechanisms at both the LED package and system levels. Consequently, the 150 W luminaire presented a more pronounced luminous flux depreciation over time, whereas the 80 W model exhibited a comparatively more stable performance.

These results are consistent with findings reported in scientific literature, which indicate that luminous flux degradation in LED luminaires is primarily driven by the combined effects of thermally induced LED lumen depreciation and aging of optical components, particularly polymeric lenses and protective covers [14], [15]. Optical materials exposed to elevated temperatures and short-wavelength radiation are prone to yellowing and transmittance loss, leading to a reduction in effective luminous flux even when electrical operating conditions remain within specified limits [16].

To support the comparison between luminaires of different wattages, a deviation analysis was performed using coefficients of variation and temporal performance trends. This methodology enables the identification of systematic degradation effects while reducing the influence of measurement uncertainty, thereby confirming that the observed differences in luminous flux behavior are physically meaningful and directly related to operating conditions rather than experimental variability [13].

Overall, the results demonstrate that higher-power LED luminaires are more susceptible to accelerated photometric degradation due to combined thermal and optical stresses, underscoring the importance of system-level evaluation and extended aging tests for the assessment of long-term performance, durability, and regulatory compliance. In this context, it is recommended that the testing period be extended beyond 6,000 hours to enable a more robust evaluation, as this operating duration corresponds to stabilized and representative operating conditions of the luminaire components.

Table 4 Maintenance of Luminous Flux shows the measured luminous flux values in the different luminaires over 6000 h of operation:

Table 4: Maintenance of Luminous flux (lm) 

Luminous Efficiency

The luminous efficiency followed a trajectory like the luminous flux. Fixtures with higher initial power showed greater sensitivity to thermal and optical degradation. The efficiency of the 150W model dropped from 116.88 lm/W to 86.00 lm/W by the end of the period, while the 200W model reduced from 195.73 lm/W to159.74 lm/W. Such values, although still technically acceptable under certain applications, indicate that optical systems (lenses and diffusers) strongly contribute to efficiency losses, even when the LEDs maintain their internal performance. Table 5 The analysis of the coefficient of variation (CV%) of luminous efficiency reinforces the observed trend. The 200W model showed the highest fluctuation, with a CV of 15.52%, followed by the 150W model (12.31%). The 40W and 80W models demonstrated greater stability over 6000h, with CVs of 11.45% and 7.85%, respectively.

These results indicate a more pronounced sensitivity to thermal and optical degradation in higher power models.

Correlated Color Temperature (CCT) and IRCA

The correlated color temperature (CCT) of the evaluated luminaires exhibited significant variations throughout the aging process, particularly for the 150 W and 200 W models. The 150 W luminaire showed a pronounced shift from 6822 K to 5311 K, characterizing a critical deviation in light coloration that is strongly associated with optical aging effects. This behavior is further corroborated by the reduction of the R9 index (saturated red) from +1 to −16, indicating selective spectral absorption typically linked to yellowing and partial opacification of polypropylene lenses, as evidenced in Figure 1.

The coefficient of variation (CV) of the CCT reinforces the observed spectral instability in higher-power luminaires, with values of 9.93% and 6.36% for the 150 W and 200 W models, respectively. In contrast, the 40 W and 80 W luminaires exhibited greater chromatic stability, with CVs of 5.92% and 3.35%, respectively. These results suggest a clear correlation between luminaire power, increased thermal and optical stress, and susceptibility to chromatic degradation. Such spectral shifts directly compromise color fidelity and may adversely affect visual perception and safety in public lighting applications.

According to CIE Publication 13.3, the Color Rendering Index (CRI), referred to in Portuguese as Índice de Reprodução de Cor (IRC), is defined as a metric for characterizing the color rendering properties of a light source relative to a reference illuminant. The general color rendering index, Ra, is calculated as the arithmetic mean of the first eight special color rendering indices (R1-R8), which represent color samples of moderate saturation and are widely adopted in technical specifications. However, Ra does not account for saturated colors or specific visual conditions. To address this limitation, the special color rendering indices R9 to R15 are defined as complementary parameters, representing highly saturated colors and specific samples, including saturated red (R9), skin tones, foliage, and other relevant materials. These indices are not included in the calculation of Ra and provide additional insight into spectral deficiencies of the light source.

Several studies have demonstrated that light sources with high Ra values may still exhibit poor reproduction of saturated red colors, a deficiency effectively captured by the R9 index [14], [17]-[20]. Therefore, R9 is widely recognized as a critical complementary metric for assessing the spectral quality and long-term color rendering performance of LED-based lighting systems, particularly in applications where accurate color perception is essential.

BUG Parameters and Photometric Distribution

Goniometric tests showed changes in the BUG parameters over time, especially in the glare index. The 80W model evolved from B2-U2-G2 to B3-U2-G2 after two thousand hours, indicating an increase in the glare component. Such variations may be associated with microfissures or imperfections in the lenses, which redirect light beams and affect spatial distribution. The 200W model, on the other hand, maintained the B4-U2-G4 classification throughout the entire test, demonstrating greater optical robustness and stability of the lens and reflector system.

Table 6: BUG Classification Over Time 

Impacts of the UVO

Test accelerated aging in UV chamber revealed degradations consistent with the results of photometric tests. A reduction in TCC was observed in all models, visible yellowing of the lenses, and loss of optical transparency. The 150W luminaire also showed the worst results in this test, indicating the fragility of its components against UV radiation. Figure 7 shows the main impacts recorded before and after six thousand hours of exposure.

Figure 7: The 150W Luminaire Recorded Before and After Six Thousand Hours of Exposure 

The correlation between UV and TCC loss was clear and consistent among the models, strengthening the hypothesis that plastic diffusers represent the critical link in the optical durability of luminaires.

Table 7: Table 6 BUG Classification Over Time 

Comparison with LM-80

Model GL 421 The only model evaluated based on the manufacturer's LM-80 was the GL 421 (200W). The comparison between the measured values and the reference curves (85 ºC and 105 ºC) indicated compliance only up to 3000h, with performance exceeding expectations. However, at 6000h, the measured flux represented only 81% of the initial value, while the LM-80 curve suggested maintenance above 97%. The discrepancy suggests the direct influence of external elements to the LED, such as heat sinks, encapsulation, and lenses. Table 8 presents the percentage comparison between the predicted and measured flux, reinforcing the importance of the systemic analysis of the luminaire - not just the LED components in isolation.

Table 8: Data Referring to the LED Indicated in the LM80 

Table 8 shows the result of the extrapolation of useful life. The estimated L70 value was over 54,000 hours, confirming the thermal robustness of the system for this model. The wiring diagram of the measurement cables and the position of the thermocouple are presented in Figures 5 and 6, which accurately illustrate the experimental procedure.