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Slash Your Factory/Office Lighting Bills

Most offices, factories and shops waste a lot of money in power for lighting. How would you like to save up to 50% of your lighting power bill . . . and get even more light into the bargain? We show you how - and have the measurements to back it up!

By Leo Simpson

In a typical commercial building, lighting accounts for about 30% of total energy consumption.

Air-conditioning amounts to about 50%, while the remainder is taken up by office equipment such as computers, copiers, printers and so on. So how can we reduce overall power consumption?

Over the next few years this question will become far more pressing as electricity tariffs increase dramatically.

Since air-conditioning is the main energy user, it behoves the building or office manager to ensure that everything has been done to minimise energy use. In particular, attention must be paid to anything which generates heat in summer, which means the air conditioner has to work even harder – and use even more energy – to overcome.

Regular servicing of the air-conditioning system (especially cleaning the filters, which you can usually do yourself), monitoring of temperature settings in winter and summer, ensuring that doors are kept closed to stop drafts and so on are all important. Ultimately, measures like window tinting and double-glazing can provide further energy savings but the initial investment will be a lot higher.

But cutting lighting energy use is the focus of this article. This came about for the very practical reason that all the fluoro tubes in the SILICON CHIP offices obviously needed replacing.

In most offices, the approach would be to have all the tubes and starters replaced, together with cleaning the diffusers. That should be done every few years as a matter of course but this simple approach will not provide any energy savings. We were looking for significant savings.

Our first step was to measure the light levels around the office and it must be stated that they ranged from just adequate to poor. In an office of about 12 x 8 metres, the levels ranged from under 150 lux to about 280 lux, at best. The average level was about 210 lux. The whole area is lit
by 12 twin-36W fittings, more correctly referred to as recessed luminaires (or in the trade as “troffers”) which have prismatic diffusers.

In our case, as we moved into this building in 2004, the tubes were probably at least six years, or around 16000 hours old – well overdue for replacement. Not only were the tubes noticeably down in emission but the prismatic diffusers were quite dirty.

The second step was to replace the old tubes in two of the luminaires in my office area with new GE Cool White tubes which have a colour temperature of 5000°K. These tubes are significantly whiter than the old tubes which have the distinct greenish hue (or “cast”) of conventional fluorescent tubes. With the new tubes fitted, the light measurement went from 210 lux to 320 lux. This was much brighter but then we decided to try some Mirabella Tri-Phosphor tubes, again with a colour temperature of 5000°K.

These were much brighter again; too bright in fact. So we opted to have just one Mirabella Tri-phosphor in each fitting. This gave a light reading of 270 lux, well above what we had started with.

But we also wanted to try NEC quad-phosphor tubes which are claimed to be 15% brighter than tri-phosphor tubes. While slowly becoming more popular, they’re not the easiest things in the world to buy (as yet, they’re not in your local supermarket), nor are they cheap.

But we found them in a Bunnings Hardware store and purchased a couple to try out.

Incidentally, we also found out while shopping around that it is getting almost impossible to buy older, single-phosphor tubes any more. The vast majority of tubes on the shelves of both supermarkets and hardware stores were in fact tri-phosphor. So at least that’s a good start!

We’re getting a bit ahead of ourselves here but we were so happy with our tests we bit the bullet and purchased a box of 25 NEC quad phosphor 37W tubes from our local electrical wholesalers, John R Turk, here in Brookvale. The cost was $316.25 including GST, or $12.65 per tube. This might seem expensive for 25 fluoro tubes but it is much cheaper than buying them retail.

With a single NEC quad-phosphor tube in each luminaire, the light was up dramatically to around 310 lux. This was great so we then did the same for six twin-36W luminaires – fitting one quad-phosphor tubes for the old tubes and cleaning all the prismatic diffusers and white-painted surfaces of the light fitting. This brought about a dramatic change. The final light reading on my desk was now 330 lux.

That’s towards the low end of the relevant Australian standard for office lighting (see separate panel: “What is the correct office light level”) but I found that it was more than enough for normal work. In fact, I found anything much greater than about 300 lux started to become a problem, especially when trying to read glossy or even semi-gloss (ie, coated) magazine pages.

Click for larger image
Inside a traditional (iron ballast) fluorescent fitting, as found in hundreds of thousands of offices, factories and shops around the country. The two ballasts are in the middle, the power factor correction capacitor is on the right, while the starters are mounted on the ends. Note the blackening of the tube ends – a sure sign these tubes are on the way out.
Click for larger image
By contrast, here's a modern fluorescent luminaire fitted with a single electronic ballast (centre-right). Note the absence of a power factor correction capacitor and starters – they're not needed with the electronic ballast. The downside of this particular fitting is that it cannot drive a single tube – you must have two fitted. But they should last longer.

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