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This document summarizes the main features of the technology used in the LED street lighting solutions of Exporlux / BlueSpan that are the basis to the predicted reliability and performance.
Solutions for LED street lighting use Luxeon Rebel, the latest generation of Philips Lumileds. This family of LEDs provides exceptional mechanical, electrical and optical characteristics, especially for this use.
Its main features are:
Mechanical Characteristics:
- Small size
- High mechanical robustness
Electrical:
- High luminous efficiency (> 100lm / W)
- Very high drive current (up to 1000mA)
- High temperature stability
- High junction temperature (<= 150 º C)
- High linearity with the current adjustment
- Reduced deterioration over its lifetime
- High lifetime (> 60.000H)
- High electric robustness
Optical Characteristics:
- High spectral selectivity
- High optical stability
- Wide range of color temperatures available
» Cool white (5300K)
» Neutral White (4000K)
» Warm white (3150K)
- High CRI (> 75)
The Luxeon Rebel used in this project presents a high electrical / optical performance throughout their lifetime.
The high luminous efficiency over 100lm / W (when polarized at 350mA) contributes significantly to this performance, since it ensures at the outset, a high global luminous efficiency (luminaire), complying with the guidelines of the energetic efficiency program EnergyStar.
The high temperature stability ensures a relatively low downgrading of the luminous flow even when considering very high junction (Tj) temperature. The following chart illustrates this fact for the color temperatures typically used in street lighting (cool white and neutral).
Since this technology does not present a catastrophic end of life (i.e. in normal operation the LEDs do not go out altogether), a new way to quantify their lifetime needed to be found. ASSIST (Alliance for Solid-State Illumination Systems Technologies) determined that 70% is the threshold at which it is possible for the human eye to detect a luminous flow reduction (related to the logarithmic integration of our eye, less sensitive to changes in higher flow levels). Thus, it was specified that an effective reduction of 30% of the luminous flow, in relation to the initial value, determines the end of an LED’s lifespan. In other words, when we say that an LED has reached the end of life at 60.000H we are in reality saying that it still has at least 70% of the initial flow.
Currently we work with B10/L70 levels, which correspond to a maximum effective reduction of the luminous flow of 30% but only on 10% of the LEDs. It is noteworthy that this level of downgrading only occurs in extreme situations, typically characterized in terms of current and temperature at the LED junction. In the case of high-performance systems, the limit conditions will never be reached (assuming normal operating conditions, for which the system was specified), which is why the levels of downgrading will be considerably lower.
The following figures illustrate, correspondingly, the lifetime expected depending on junction temperature and thermal PAD. These values relate to a confidence interval of 90%.
Luminaires for use in the LED street lighting were designed and developed according to the highest demanding standards, ensuring high quality lighting and energetic efficiency. Additionally, given the high lifetime presented, these allow a significant reduction in operating costs.
