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| Elliott Sound Products | LED Lighting Comes of Age - Part 2 |
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My excitement about the future of LED lighting continues unabated. As noted in Part 1, Spectrum Lighting (in Brookvale, NSW Australia) was kind enough to continue to donate and loan me a variety of LED lighting equipment. This has enabled me to perform further tests, and modify some otherwise useless products (such as solar garden lights) to be not just decorative, but actually cast enough light to be able to see at night. Somewhat predictably, the solar component is no longer used because the panels of the cheap lights are simply too small to be useful, and the Ni-Cd cells are the cheapest (and poorest quality) that one can find.
A traditional fluorescent lamp on the back verandah has been replaced with a new fitting that was made using the insides of a broken LED tube-light, and is not only extremely bright, but has the added benefit of almost zero insect attraction. Because LEDs have no ultraviolet light output, most insects are completely disinterested. A luminaire that one would expect to see full of insect carcasses has none at all after 6 months. Because insects aren't attracted, there are also no spider webs, because the spiders seem to know that as a 'food-attraction-device' the LED lamp is useless. Compared to the fluoro that the LED light replaced, the difference is huge!
While it is both heartening and welcome, the number of LED 'globe/lamp replacement' products becoming available is probably unfortunate in some respects. It is to be expected, but places unrealistic expectations on the replacement products. They have to have a similar 'look and feel' to the products they replace to satisfy the market, and this makes the construction of these lamps a serious compromise. While some dedicated LED lamps do exist, these are presently in the minority.
The real future of LED lighting will be based on the production of complete fittings. The fitting itself will have the ability to act as a heatsink, and the 'lamp' will not be replaceable. Because LEDs last so long, it's expected that in many cases, a normal renovation cycle will probably see the fittings replaced before the light output has fallen significantly. This may be 20 years or more, and if the heatsinking is good enough, a 30 year life for typical use is not unreasonable.
Heat is ultimately the biggest obstacle to be overcome with LEDs. Unless there is some means of keeping the temperature as low as possible, the life of the LED is reduced. The reduction can be quite dramatic, but like everything else in technology, there is a lot of work going on. One approach is to allow the LED chips to operate at higher temperatures without premature failure. Many of the currently available high-end LEDs are rated for at least 50,000 hours at elevated temperatures. If the temperature can be kept low with a well designed luminaire/heatsink assembly this already long life can be extended.
As users - both household and commercial - start to accept that LEDs herald a new era in lighting, we can expect to see a departure from the separate luminaire and 'bulb' (or tube) mentality. This promises to be exciting, because it will be possible to make light fittings that have never been possible with any incandescent or compact fluorescent lamps. Lighting fixtures that lie flat against the ceiling, projecting no more than about 20mm from the surface can be done right now. Depending on how much light one expects, the heat generated in such a fitting may be negligible, so cooling becomes almost a non-issue.
Figure 1 - Customised LED Light Fitting
Using the insides of a LED tube light that had been broken, I built a light fitting for the back verandah (as noted above). The entire fitting extends only 40mm from the ceiling, with the vast majority of that needed to accommodate the curved diffuser. Heat is extremely low, there's no UV and no insects, and it comes on at full brightness even when the outside temperature is only a couple of degrees Celsius. Much lower temperatures won't cause any distress, but they just don't occur in Sydney.
One thing that I've noticed recently is the huge amount of effort being put into specialised ICs for LED power supplies. For example, National Semiconductor (now Texas Instruments) has released the LM3445 controller. This is designed to provide a constant current through the LEDs, with an integral pulse width modulated (PWM) dimmer. The dimmer part of the circuit reacts to the setting of an ordinary TRIAC based dimmer, and allows the lamp (or luminaire) to operate from any standard dimmer, and provide full brightness control based on the relative on and off times of the AC waveform. This level of control is not available with any fluorescent lamp, and no-one seems very interested any more. It's safe to say that the combination of continued bad press and user complaints has dealt the CFL a potentially fatal blow - I get regular emails from people all over the world who are very annoyed that they are forced to use CFLs, regardless of whether the fitting is suitable or not. While I still use CFLs where it's sensible to do so, there are quite a few places in both my home and workshop where they are completely inappropriate - either because of very short on-time and regular switching, or because the fitting is poorly ventilated.
Because LEDs don't care if they are turned on and off 100 times a day (or 400 times a second for that matter), the limitations of switching cycles don't apply. CFLs and incandescent lamps most commonly fail at the moment of switch-on. LEDs are not affected at all, although power supplies may fail. The answer is to make the power supply replaceable, and leave the LEDs permanently attached to the light fitting.
As noted above, specialised ICs are now available that will dim LED arrays based on the duty cycle of the AC waveform. Other easily adapted options are C-Bus, DMX512 or even the venerable 0-10V analogue dimmer standard. There are already a great many LED stage lighting cans that have integral DMX512 controllers available, and while these are not as bright as an incandescent PAR64 can, they don't require an external dimmer, colour wheel or gels, and run almost cold. They are also very lightweight and draw minimal power. This is an area that will continue to grow rapidly, and will increase the use of innovative lighting - even for small bands or stage/theatre groups.
Being perfectly dimmable, lighting can be made adaptive, so that only as much light is created to maintain a consistent level of illumination in a given area. A sunny office area might need no artificial light during bright days, but the lamps can be programmed to provide a boost if needed. This can even apply should a cloud pass overhead - the LEDs will simply fade up and down as needed, maintaining exactly the light level expected for the tasks performed in that area. The potential for huge energy savings and far better lighting for homes and businesses is obvious.
One application of LEDs that is starting to make inroads is their use in cars. I built a couple of dome lights for my cars that are simply astonishingly good. Power consumption is much lower than the traditional globes that were used before, and the light output is many times higher. The LEDs are running at a current that's a bit higher than the design value (there are 18 x 5mm LEDs for each dome light), and although this will shorten their life, they will almost certainly outlast the cars anyway.
LEDs are a natural for car dash lighting too - the use of small incandescent lamps has always been a problem - especially when they fail. As anyone who has tried to replace lamps in a car's dash will know, it is often an exercise in extreme frustration, coupled with colourful language and skinned knuckles. Since LEDs can be expected to outlast the vehicle, replacement becomes a thing of the past, and the lighting can be placed where it's most needed, rather than somewhere where the manufacturer might consider 'accessible'. Stop and tail lights, blinkers (indicators), number plate and side lights, all are ideal for LEDs. Already, some car manufacturers are using LED headlights - Audi R8 and Lexus LS at the time of writing, but with more to come. Expect to see complete assemblies for front and rear light clusters, and the replaceable globe will be a thing of the past.
Interestingly, there are already many LED replacement lamps available. However, in Australia at least, it is (apparently) not legal to use them for road-registered vehicles because they were not supplied as part of the OEM (original equipment manufacturer) bill of materials, and haven't undergone 'proper' testing. Frankly, I think this is extremely silly. Normal incandescent lamps can fail at any time, and who knows where they came from and whether they emit the correct amount of light. Any LED replacement that has roughly the same light output will not only last a great deal longer (improving road safety), but will do exactly the same job as the originally specified lamp. The same problem seems to exist in the UK, and there (and likely here in Oz too), it seems to be related to the rated power (in Watts), but with zero consideration for the actual light output.
The extra efficiency of LED car lighting is not wasted either. For every kilowatt of electrical energy used in a car, that's a kilowatt that comes from the petrol or diesel fuel. While most people probably don't think about it much, the laws of physics and the tax man both frown upon the idea of 'something for nothing' - if energy is used, it must come from somewhere. While lighting is not a big drain on a car's electrical system, every small saving is worthwhile. If it also improves reliability to the extent that the lamps last for perhaps 20 years with no failures or significant deterioration, then that's a real bonus. 50,000 hours (the typical claimed life of LEDs at present) is 5.7 years of use, 24/7. With normal use of perhaps 3 hours a day (or night), the LEDs can theoretically last for over 45 years!
Figure 2 - Rebuilt 'Solar' LED Garden Light
Another common area is garden lighting. Unfortunately, most of the LED garden lights on offer are 'solar powered', but the cheaper ones typically use very small solar panels, the cheapest (and nastiest) Ni-Cd cells available, and most often a single 5mm LED. To say that they are pathetic is high praise - even those in direct sunlight for much of the day stopped working after a couple of months. The main reason I bought the lights I have was because they have a rather stylish stainless steel bollard, and it was a simple matter to remove the existing blue LED and the other electronics, and substitute a small section of high brightness strip-light with 3 surface-mount LEDs on each section. This is mounted on an aluminium heatsink/reflector, and a bridge rectifier converts the incoming 12V AC into DC for the LEDs. I increased the number of lights (there are now 8 in all), and the combination not only gives far more light, but all 8 LED lamps draw less current than just one of the incandescent lamps they replaced. The first unit I installed as a test used 6 LEDs, and was much, much too bright.
This is a relatively cheap way to get some excellent garden lighting, and in my case, good lighting is essential because of the trees that make the footpath almost invisible at night. Because the overall power is so low, it's no longer a cause for concern over the energy used.
Fridges and microwave ovens are prime candidates for LED interior lighting too. This leaves only the oven light that needs to be incandescent, since no other lamp type can withstand the high temperature.
Possibly more than anything else, it is the ability to control and/or dim LEDs with exceedingly low losses that will make them the choice for many lighting applications, some of which haven't even been thought of at this stage. It's probably inevitable, but we can fully expect that LEDs will be used for lighting things that simply don't need illumination, but will be used "because we can". Because they are small and very unobtrusive, it becomes possible to put light into places where lights have never been used before. Fortunately, the power consumed by such frivolous applications will be fairly low, so will have very little impact.
The applications are endless, even for traditional lighting. Chandeliers (some of which may use 20-40 lamps or more) no longer have to use mains rated cable with thick insulation and bulky lamp sockets, because all wiring can be low voltage and easily concealed, and there is no requirement at all for a socket. More conventional wall and ceiling lights can be made to lie almost flat against the surface, with no need for recesses. Wiring can be low voltage, and it's probably only a matter of time before newly built homes and businesses will use a separate low voltage (probably 12 or 24V DC) circuit for at least some of the lighting. This also allows battery backup, so the whole house isn't plunged into darkness if there's a power outage. If the lights can be dimmed, this reduces the power used quite dramatically, while still providing enough light to move around safely.
This is certainly a better and safer alternative to candles and torches (flashlights). The former have caused many house fires, and the latter always have flat batteries when they are needed most. One could even use the principle of some of the latest wind-up torches that are available quite cheaply - a hand operated generator to provide a battery top-up should the blackout last longer than expected. Well, perhaps not, but it's certainly an option.
These articles are a work in progress, as there are more LED ideas yet to be covered. Page 1 covers some of the products I've tested, and Page 3 has some additional data.
There are no references as such, because this article is more of a philosophical discussion than anything else. I must thank Spectrum Lighting for providing me with a number of broken LED tube lights, which have given me the opportunity to carry out more experiments and build test luminaires, garden lights, etc.
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