When selecting LED light fittings as a replacement for traditional low bay/high bay luminaires, it’s important to understand that it’s the lumens that count, not the watts. Simon Miles, Sales Director of Carbon8 Lighting, explains more.
A stable, reliable LED low bay/high bay light fittings have become available over the last few years they’ve become the obvious solution for lighting upgrades in many projects.
In the past, when high or low bay lighting was upgraded, it was essentially a matter of replacing like-for-like – 400W SON with 400W SON, for example. With LED light sources, the situation isn’t as clear cut and there’s a real danger of over-lighting a space.
Industry guideline
This situation dates back to the early days of LED high/low bay fittings, which were typically achieving 80-90 lumens per watt. It then became an industry guideline that a ratio of around 3:1 was suitable for calculating the wattage of an LED fitting that was replacing a traditional fitting. So, for instance, a 400W SON or metal halide fitting would be replaced with a 150W fitting producing 12,000 to 15,000 lumens.
In fact, this 3:1 ratio has become ingrained in the psyche, to the extent that many people forget they’re buying light, not watts. This ratio, however, doesn’t take account of the higher lumen outputs of more recent LED fittings. Many people are stuck on the idea that 400W HID fittings should be replaced with 150W LED fittings with no consideration of the actual light output.
To give an example of how high/low bay LED lighting has evolved, the 150W LED high bay fitting we introduced in 2015 produced just over 14,000 lumens. This was superseded by the 120W Discus high bay, producing over 18,000 lumens. Now the current Discus Gen2 is available in a 90W version that produces 16,000 lumens, while the 150W version delivers over 25,000 lumens.
So, to put this into perspective, if the 3:1 ratio is adhered to, then replacing a 400W HID fitting with a 150W Discus Gen2 would provide around 40% more light than was actually needed. Not only would this waste a lot of energy, it would also ‘over-light’ the space.
Thus, in the example above, the 90W LED high bay would be a more suitable replacement for a 400W HID fitting, giving the correct light levels for that area whilst reducing energy consumption and costs. Further cost savings would be achieved through the simple fact that a 90W lamp costs less than a 150W lamp.
Creative juices
The factors discussed earlier assume that the lighting is being replaced on a one-for-one basis, which is the usual approach. However, with LED fittings there is an opportunity to exploit the higher light output that is available from LEDs and also take advantage of the directional nature of LED light sources. This latter characteristic means that less of the light output is ‘lost’ in the luminaire.
In this scenario, it may be possible to deviate from the one-to-one approach and achieve the required light levels and distribution with fewer luminaires than had previously been installed. Combined with the longer life of LED light sources, compared to LED, this would result in a significant reduction in maintenance costs.
At the end of the day, the best solution will be determined by the nature of the space and the existing lighting. The important aspect is to move away from 3:1 ratios and think in terms of actual light output.
