Lighting : Lighting August 2016 - Vol 36 Issue 4
32 LIGHTING MAGAZINE | August/September 2016 August/September 2016 | LIGHTING MAGAZINE 33 potential saving in reduced initial light levels, which translates to the possibility of fewer luminaires or lower lumen output (and energy consumption if similar performing product). Either way this offers a potential financial saving on the cost and/or operation of the lighting installation. BENEFITS OF L70 SELECTION BASED ON INSTALLATION LIFE The energy conservation benefits of selecting a lamp’s L70 based on the expected installation life can be considered by a comparative analysis against the baseline of a lamp with an L70 equal to the installation life. That is, the initial light level is 143% of the target lighting level. Figure 9 is such an analysis for the example installation life of 60,000 hours. There is no energy savings below an L70 of 60,000 hours as the installation will require re-lamping before the installation’s end of life. As the lamp L70 increases beyond the installation life the energy savings increase but in a diminishing manner. To understand the significance of this potential energy saving, we need to have an appreciation for the typical life of a lighting installation before replacement or refurbishment occurs. Based on anecdotal research, Table 1 presents some fairly typical usage boundary conditions for four common applications. Residential typically has low lamp use per day (1 to 5 hours) and a relatively long period between installation refurbishment (15 years). Small enterprise offices have slightly longer daily hours of use (8 – 10 hours) and a longer refurbishment cycle (20 years), whereas large offices have longer daily hours of use (12 – 18 hours) but a shorter refurbishment cycle (10 years). Finally retail and hospitality typically has a much shorter refurbishment cycle (7 years) with a very high daily hours of use (16 – 24 hours). These figures create different ranges of operational life, (before fixtures are replaced), for installations, in the various building sectors: approximately 5,000 to 25,000 hours for residential; 35,000 to 50,000 hours for commercial office (small and large) and approximately 40,000 to 60,000 hours for retail and hospitality due to very long opening hours of this sector. Figure 10 provides a substantive analysis of potential energy savings for installation operational lives from 5,000 to 100,000 hours for LED lamps with L70’s from 5,000 to 150,000 hours. Examination of these curves indicates that the potential energy savings asymptotes to a theoretical maximum of 30% (where a lamp has zero lumen depreciation, L70 = ∞). All of the curves can be represented by a single curve on the similar graph where the lamp lumen depreciation on the dependent axis in represented in multiples of the “installation life”, Figure 11. Some interesting “rules of thumb” can then be drawn from this analysis in relation to length of L70 relative to installation life and the potential energy savings (relative to a L70 lamp lumen depreciation lighting design), Table 2. IMPACT ON CURRENT LIGHTING DESIGN When we reflect on current design practices with traditional lamp technologies which have LLD’s ranging from 0.80 to 0.95, we find they are already achieving similar energy conservation levels relative to a baseline design of a LLD of 0.70, Table 3. So without selection of a lamp with an L70 which is two to three times the installation operational life we are missing out on energy savings currently received. Maintaining this benefit means there is no erosion of other real savings realised from improved efficacy of LED over traditional lamp technologies and no labour and asset costs associated with scheduled bulk lamp replacements during the life of the installation. (Obviously spot replacement for a minimal number lamps, due to random early failure of electronics, will still occur.) Figure 9. Potential energy savings for lamps with increasing L70 for an installation life of 60,000 hours. Figure 10. Potential energy savings for lamps of differing installation life for increasing lamp L70 values. Table 1. Typical lighting operation hours and refurbishment cycles Situation Residential Small office Large office Retail/ Hospitality Hours per day 1 5 8 10 12 18 16 24 Days per week 7 7 5 5 5.5 5.5 7 7 Hours per year 365 1825 2087 2607 3441 5162 5840 8760 Refurbishment cycle (years) 15 15 20 20 10 10 7 7 Total hours of operation 5475 27375 41714 52143 34414 51621 40880 61320 Figure 11. Potential energy savings for lamps of increasing lamp L70 values in multiples of “installation life”. Table 2. Rules of thumb for potential energy savings for increasing L70 of LED lamp L70 (in multiples of Installation life) Potential energy savings (relative to a L70 lighting design) 1.5 10% 2.0 15% 3.0 20% 5.0 25% Table 3. Current energy conservation for typical LLD’s of traditional lamp technologies Lamp Lumen Depreciation Current energy conservation (relative to a L70 lighting design) 0.80 12% 0.85 17% 0.90 22% 0.95 26% CONCLUSION Light sources have become an asset rather than a consumable and they are becoming a connected asset. Consequently the life of the lighting installation has become the limiting factor in the lighting design process not the life of the lamp. Therefore this paper has presented an argument for careful consideration and analytical examination of the implications and opportunities so as to provide a more cost effective, life-long operation of the asset (lamp) in a lighting installation with a finite life.
Lighting June 2016 - Vol 36 Issue 3
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