See The Light, Not The Watts Suggests Simon Miles Of Carbon8lighting
- Published: Thursday, 22 June 2017 11:20
LED luminaires are the obvious choice for lighting upgrades in many types of project. However, it’s important to focus on the lumens, rather than the watts, suggests Simon Miles, Sales Director of Carbon8lighting
Readers will have seen significant improvements in the performance of LED lighting in recent years, making them the lighting of first choice for many applications. This is now true even for applications requiring high light outputs such as high bay and low bay projects.
In all projects that involve an upgrade to LEDs it is clearly important to select the right fittings, located in the right positions, ensuring the space is lit to the correct lux levels. Doing this effectively means that contractors need to be aware of the most recent development in LED lighting, which may require a different approach to what they’re used to.
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 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 (e.g. 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 The high bay referenced above was quickly superseded by a 120W version capable of delivering over 18,000 lumens and more recent models can give 16,000 lumens from the 90W version and over 25,000 lumens from the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.
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% 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.