Every once in a while, the way that we see the world shifts and the way that we do things needs to be reviewed. The basic approach in commercial lighting, the sector from which so much lighting product derives, is the recessed fluorescent 600×600 modular luminaire. Designed to sit in a conventional suspended ceiling, this is the default lighting option for shops and offices everywhere.
Improved system efficiency in this type of fixture has relied on two things, one in the control of the manufacturer and the other not. The efficiency that the manufacturer has had nothing to do with, but has benefited enormously from, has been the improved light output of fluorescent lamps – to the general benefit of all users. The improved efficiency that has been less welcome, and which has been fully in the control of the manufacturer, has been the photometric performance of the luminaire.
The most effective way to get light out of a row of fluorescent lamps is to wrap a specular reflector around each tube so that as much light as possible heads downwards into the space. Unfortunately, this is one way of describing the ‘cat2 luminaire’ that became the reference specification for office lighting in previous editions of lighting guides for offices.
It was originally intended to prevent glare onto computer screens, but since then screens have undergone their own ergonomic improvements, rendering cat2s unnecessary. There are many reasons to celebrate the end of the cat2 luminaire, not least the way that it left rooms looking like caves, but with it’s use so deeply ingrained, it seems that the ‘cat2’ luminaire is destined to live on. Unless . . .
Looking at things in a different way
The only justification for the continued use of recessed fluorescent modular luminaires is habit – which dies hard, as we all know. But if we embrace a new view of the world, the world as it now works, we can see a much better – and more efficient – way of lighting our commercial spaces. The LED panel is becoming a very popular alternative to the fluorescent cat2 luminaire, and here’s why.
If we look at a direct comparison between the performance of the LED panel and the fluorescent modular luminaire we can see the immediate benefits for shifting from old to new technology.
Let’s take a generous office space, measuring 10m x 10m, with a ceiling height of 3m and standard surface reflectances, as might be expected in an office environment. We can produce a design layout that provides a like-for-like comparison between the LED and fluorescent options.
The performance calculations show that there is very little difference between the two lighting options. If anything, the LED panel is delivering a better illuminance across the space, as is indicated in the pattern of light shown in the false colour plots.
There is a clear improvement in the quality of light in the room. The stark light produced by the cat2 photometrics is replaced by a much softer appearance of the space, offering better illuminance of the walls and an overall improvement in the visual environment, as is required by the SLL Lighting Guide 07: Offices.
Return on investment
The financial figures demonstrate the immediate benefits of shifting from fluorescent to LED technology. Although the V-TAC unit costs slightly more to purchase, the savings in energy consumption return the additional capital expenditure within 12-15 months of operation.
A warning word about LED light panels
Like much of the new LED marketplace. There are many products available, some of them very cheap – too cheap! When selecting an LED panel, always make sure that the product you select satisfies these criteria:
Circuit Watts: Make sure that the figure that’s being quoted relates to the total wattage of the luminaire, including any parasitic energy used by the driver in the circuit.
Lumen output: Firstly, make sure that the lumens being autoed relate to the output of the luminaire NOT the lumen output of the LED array inside the luminaire housing.
LED outputs continue to increase and, at first sight, this is good for energy savings. But there is a practical limit to output levels. Office lighting requires a good level of uniformity across the space. If a scheme is designer around luminaire delivering too much light the tendency is to increase the spacing to maintain a sensible average illuminance; sat 350 Lux. It’s better to use more luminaires with a lower output as it makes life better for the people working in the office.
Use the higher outputs where there are unusual conditions, such as much higher ceilings, or in a retail environment.
Colour temperature: With LEDs, the cooler the light colour, the more energy-efficient it is. That means that many companies only offer cool colour temperatures, sometimes no lower than 6000K. This is not an acceptable situation; there should always be a choice in light colour.
Colour rendering: Do not accept anything less than 80 as a CRI value. Ever.
Power Factor: Make sure that the luminaire has a Power Factor of greater than 0.9.
Glare rating (UGR): It’s a legal requirement that office lighting satisfies the Universal Glare Rating Index by delivering a UGR of less than 19.
All of these factors are met within the V-TAC range of LED panels.