Electrical Contracting News (ECN) April 2017 - Page 61

SPECIAL FEATURE

LIGHTING

SPECIAL FEATURE

For example , in the past replacing existing lighting was pretty straightforward , in terms of sizing the light sources . If the old installation was using 400W SON then so would the new system – or maybe it would upgrade to 400W metal halide . With LEDs though , the situation is a bit more complex – because with LEDs it ’ s the lumen output that counts rather than the wattage .
Of course , many contractors have been aware of this for some years and may well be accustomed to a rough calculation along the lines of a 3:1 ratio – so that a 400W high intensity discharge ( HID ) lamp ( eg . SON or metal halide ) is replaced by a 150W LED source ( for instance ). The trouble is , the idea of the 3:1 ratio seems to have become firmly entrenched in some minds , so that lighting upgrade projects are still being based on this , rather than taking account of the higher light outputs of modern LED luminaires .
A few years back the 3:1 ratio made perfect sense . Early LED high bay / low bay fittings typically achieved 80-90 lumens per watt so a 150W fitting would produce 12,000 to 15,000 lumens and would be a suitable replacement for a 400W HID lamp . The first LED high bay fitting we introduced in 2015 , for instance , produced just over 14,000 lumens .
However , LED fittings have evolved . The high bay referenced above was quickly superseded by a 120W version capable of delivering over 18,000 lumens and more recent models can give 16,000 lumens from the 90W version and over 25,000 lumens from the 150W version .
Appropriate subsitute
This clearly illustrates why the 3:1 ratio is no longer viable . Replacing a 400W
HID lamp with the latest 150W LED high bay would produce about 40 per cent more light than is needed , resulting in a significant waste of energy . The 90W version would clearly be a more appropriate substitute , saving the end client money on energy , with further savings on capital costs since 90W lamps are cheaper than 150W lamps .
Another important factor with LEDs is that they are directional , so in a luminaire that has been optimised for use with LED light sources less of the light is ‘ lost ’ in the luminaire – compared to HID fittings . This is why it ’ s important to select luminaires that have been designed for use with LEDs from the ground up , rather than having been simply tweaked a bit from conventional luminaires .
The directionality of LEDs also makes it possible to be a bit more creative . For example , most lighting upgrade projects are carried out on a one-for-one replacement basis to take advantage of the existing cabling . This is why it ’ s important to get the light output right .
However , in some circumstances it may be possible to exploit the LEDs ’ directionality to achieve the required light levels with fewer luminaires than were used in the original installation . In this way , both the capital and maintenance costs are reduced for the end user – adding the sort of value that often brings contractors repeat business .
In summary , the key to providing the best LED solution is to be aware of how this lighting technology is evolving , rather than getting stuck in the past with outdated ratios that seek to compare two very different types of light source .
There has been significant improvements in the performance of LED lighting in recent years .

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April 2017 | 61