Using alternative 'B' figures compared to standard TM-21 projections can: 1) Result in an overlit scheme and therefore higher lifetime costs 2) Cloud judgement between different lanterns since there is no standard to ensure manufacturers use the same calculation. By comparison, TM-21 is the same across all manufacturers Using B50 is the most appropriate measure to provide consistency with Maintenance Factor principles whilst maximising life and efficiency. Of course it's never quite that simple. Whilst there are clear benefits to using TM-21 and ignoring any 'B' claims, the problem with TM-21 is that an LED with a high degree of variation in lumen maintenance between LED samples is treated the same as an LED which has a very consistent lumen maintenance between LED samples. It is therefore desirable to specify an LED source that has as little variation in lumen maintenance performance as possible. This can be done in a consistent and comparable way by specifying minimum observed variations in the LM-80 test results (see beige row in Figure 1). Ultimately, using more energy than required to meet the standards is clearly not desirable. So, why ask for a performance metric such as L80B10 that not only causes this and is open to manipulation, thus impacting the ability to compare luminaires?
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