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SELECT SOFTWARE CORPORATE

Lighting Equipment News Editorial 2000
James Hooker L.E.N.

As I neared the conclusion of my 320-mile drive, I found myself travelling towards Great Yarmouth as David Copperfield had done in the famous Dickens novel, trying to track down a remote farmhouse with great expectations of finding something new related to the fields around copper wires for controlling discharge lamps.  It seems strange to find such a high-tech centre of expertise nestling in amongst the vast expanses of Constable landscapes, but sure enough my journey had most definitely been well worth the effort!  The company is EnLight Technologies Ltd., at the heart of which is father and son team Les and David Aarons who’ve been quietly doing some rather neat stuff with electronic ballasts while we’ve all been focussing our attention on what the big boys are up to.

They’ve approached the task of making an HF ballast from a totally new standpoint, working as computer software engineers rather than lamp circuits experts.  The result is a single totally digital device which is capable of driving almost any fluorescent lamp in existence – from CFL’s through T5, T8, T12, Circlines, U-tubes, even the exotic American high-output T17’s as well as high pressure sun tanning tubes.  The stunning advantage of this innovation is the fact that one single ballast can drive any wattage lamp or combination of up to four lamps as long as the total load is below approx. 200W.  It also operates on AC or DC voltages from 90-265V – so just imagine the savings through reduced stocking and simplified production which could be passed on to the consumer if manufacturers had to make only one design for the whole world market!  Its wide input voltage range is of particular significance to developing countries where fluorescent lamps cannot presently be used due to the frequent and prolonged dips in mains voltage, but this is the first ballast capable of reliably operating under such conditions.  They are also claiming that this device has 60% fewer components than competitors models, which should translate into an immediate saving in production costs.  Driving four 36W or 18W T8’s is of course no problem at all, and it’s also the first ballast in the world capable of powering a pair of 8-foot tubes.  Now if you thought all that was smart enough, add the fact that this is also fully dimmable, again capable of dimming any tube at all, and you start to realise why this product has already picked up numerous awards such as the International Environmental Invention of the Year Gold Medal, as well as being one of the first Millennium Products chosen by the Design Council.  And no this thing doesn’t radiate like after Nagasaki, they’ve completely sorted all the EMC issues as well.  So how did it all come about?

The dynamic duo run another company called Select Software, who were asked to design an efficient system that would dim both cold-cathode neons and incandescents on the same channel down to very low intensities.  It struck them that using an 8-foot fluorescent tube would be much easier than neon in many cases, but of course there is no dimmable ballast on the market for 8’ tubes, and even 6’ dimmable ballasts are scarce and do not always work well.  So they set about making a new ballast to dim 8’ tubes, and along the way discovered that their unique technology could in fact drive any tube at all.

Conventional dimmable ballasts, like for example the superb Philips HF-Regulator, achieve dimming by adjusting the frequency at which the lamp is driven.  The ballast normally operates at 48kHz with the lamp at full power but by increasing the frequency towards the upper value of 90kHz, the impedance of the stabilisation coil rises resulting in a lower lamp current hence light output is reduced.  This technique works well, but it is only possible to dim down to about 10% before the tube becomes unstable and flickers out.

What is different about this design is that the lamp is supplied with not one but two HF signals which can be independently varied, and the constructive and destructive interference between them is what allows the lamp to be dimmed - or indeed tuned to suit whatever lamp rating happens to be installed at the time.  The two waveforms are superimposed in the choke coil and an isolating transformer ensures that the output voltage is floating with the lamp electrically isolated from the power source.  This prevents capacitative transfer of the HF signal to the glass tube, which could otherwise cause an unpleasant sensation with possible undesirable consequences if the lamp is touched whilst illuminated.  A further advantage of the twin-signal technique is that the control circuitry only has to operate at half the voltage, extending component life and simplifying insulation – it is only when the two signals are combined that the full power is developed. 

With reference to the waveform diagram, note that when both signals are perfectly in phase with each other, the amplitude is doubled and this represents 100% power output.  By making one signal exactly out of phase with the other, they cancel each other out and there is no power supplied to the lamp.  But by making one pulse train lead or lag behind the other by 90 electrical degrees, it will be seen that lamp power is halved because it is only “on” for half the time.  Of course any power between 0% and 100% can be achieved simply by adjusting the relative phase differences of the two pulse trains.  At low light intensities, lamp stability and the absence of striations within the discharge can be maintained with feedback circuitry which adjusts the drive frequency of each individual pulse train as well as still controlling the synchronisation of each.  They claim that this allows all tubes to be dimmed down to below 1% intensity, even for traditionally ‘difficult’ lamps such as 8’ linears and the 42W triple-turn CFL.  They are also claiming that lamps dimmed on their ballast exhibit superior colour control, staying whiter at low intensities without acquiring that reddish hue which is normally apparent due to changes in the way the mercury discharge stimulates the phosphor coating. 

The totally digital nature of the EnLight ballast enables it to be connected directly to any type of network protocol.  There is no need to employ an actuator when connecting it to a Building Management System, and it works with all addressable and non-addressable communication protocols such as DALI, EIB and Lonworks.  The intelligent software within the ballast can be interrogated via conventional twisted pair communication links to report on such things as power consumption, lamp life, ballast life, energy saving monitoring and of course this can be done remotely over the internet.

For the past two years EnLight Technologies has been securing worldwide patents for its unique product.  They will continue to develop advanced lighting controls, but are now looking for a suitable manufacturing partner – so if you think you’re up to taking it on get in touch with us.  And watch out soon for an equivalent device for HID lamps!


          

Dimming discharge lamps. 

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