Technology: Are all LEDs born equal?
Technology: Are all LEDs born equal?
Simon Luckhurst explores the differences to consider before investing in LED fixtures
The development of lighting technology has, at times, been surprising. Paradoxically, for all of the benefits and applications we see becoming possible through new LED innovations, the core industry is keen to make these fixtures mimic their incandescent forbears. We’ve witnessed a similar transition in audio with digital mixing consoles. Despite being free from the traditional constraints in terms of signal path and workflow, early digital desks did little to advance procedure – at least at the manufacturer level. The aim was to introduce the technology to consumers in a familiar format while still appealing to professionals with decades of analogue experience under their belts. In the years since, we’ve seen workflows evolve and mature as audio engineers further exploited these new potentials, but it takes time for mindsets to shift.
LED technology is in a similar boat. For much of the last decade, LED lighting fixtures have been compared and contrasted to traditional tungsten and filament models. Their job has been to replace the work of those fixtures that were in widespread use in the past, rather than to evolve the lighting design.
This is perhaps not unsurprising. As manufacturers look for new ways to exploit LEDs, they often see inspiration from the technologies LEDs seek to replace. One quick example would be the unique shift in colour temperature associated with dimming incandescent fixtures. When power is turned off to an LED, the light fades uniformly. In an incandescent bulb, the colour gets warmer as the output fades.
We’ve been so used to witnessing this effect over the years that it now feels entirely natural. Attributes like this are things that manufacturers were keen to replicate for some time. The same thing happened in our homes. Many consumers didn't like the first LEDs on the market, feeling that the bright, white light they output was cold and sterile and more like office fluorescent strip lighting. So, a great deal of R&D when into learning how LEDs could mimic the soft, warm glow of normal bulbs.
This begs the question, are all LED fixtures the same?
While there may be differences at a finer level, there are many advantages common to all LED fixtures. The biggest, and often the primary, reason for most people making a switch to LED lamps is the substantial energy savings that can be achieved. With ever-increasing energy rates, the budget for a large conventional rig that would be necessary to create a proper professional stage production is increasingly being squeezed. Because of their lower power consumption, significantly more LED fixtures can be deployed while still providing an overall energy saving. Much of this saving comes in the form of reduced heat output, which in itself offers an additional safety benefit. Obviously, though, some LED fixtures are more efficient than others.
One of the areas that really separates the cheaper and more expensive LED fixtures is dimming. Without getting too technical about what exactly is going on ‘under the hood’, LEDs don’t dim by varying the current to them. They are either on or off. Their apparent brightness is the result of the LED diode flashing on/off at high speed. The faster the flashes, the brighter the output.
The diode does not allow any electricity to pass through it at all until a certain voltage is reached (the threshold point) and then, once this threshold is exceeded, electricity passes through freely and the diode emits 100% of its potential light output. This is also why cheaper LEDs don’t tend to look great on screen. Lacking the fast refresh rate necessary to blink the LED at a high enough speed to keep up with the cameras, the resulting image appears to flicker. In truth, this is not the fault of the LED module itself but the use of low-cost electronics in the cheaper models.
What you're paying for in expensive fixtures is higher-power LED emitters, better optics, sophisticated electronics that keep the light from flickering on video, and high-quality electronics and heat sinks to help ensure that the electronics last as long as the LED emitters.
Almost all manufacturers list lifetime specs for their LED products in the 10,000s of hours, so how important a consideration is a fixture’s stated lifetime? While this might be a useful guide, they are just that: a guide. Perhaps the various components making up the fixtures are individually rated to match that specification but if, for example, the wiring connecting those elements is of a subpar standard, how likely is it for that fixture to operate flawlessly for thousands of hours? The cheaper the fixture, the more susceptible it is to unexpected premature failure.
Even with next-to-no knowledge about lighting fixtures, a novice can arm themselves with a few tricks to aid in judging the quality of a fixture.
Weight. Good-quality electronics are typically heavier than low-quality alternatives, while all LEDs require heat dissipation, normally in the form of aluminium. There are high-powered LED fixtures on the market that also boast a very light weight, but these are likely sacrificing the things needed to ensure a long lamp life.
Output quality. Naturally, all LEDs output blue light and yellow phosphor is applied to the diodes. The combination of blue and yellow photons produces a white output. In a typical phosphor white manufacturing process, a phosphor coating is deposited on the LED die. The exact shade or colour temperature of white light produced by the LED is determined by the dominant wavelength of the blue LED and the composition of the phosphor. But the thickness of the phosphor coating produces variations in the colour temperature of the LED. The cheaper the phosphor manufacturing process, the less uniform the light output – meaning the colour from one fixture might be slightly different from another of the exact same model.
Manufacturers attempt to minimise the colour variations by controlling the thickness and composition of the phosphor layer during manufacturing. Furthermore, over time the blue die and the yellow phosphor will degrade and this results in the light shifting colour. It can also produce unexpected colours if the device is operated at a different current or operating temperature. Cheap LED lights generally don’t have good CRI, as this requires high-quality phosphor. Some manufacturers have gone to great lengths to focus on the colour output of their fixtures as a benchmark of their quality, for example ETC’s ColorSource range.
Construction. Exterior features such as IP-rating for ingress protection are typically only found on high-quality fixtures, as the manufacturers have to spend time and money testing and certifying their products. If the paint or powder coating has not been applied well, there might be a good chance that the inside construction is also cheap.
This is not a complete checklist, but a summary of the some of the main considerations. Basic features such as DMX control may not even be possible on the cheapest models.
Obviously, there will always be big differences in price, for any technology. Churches are understandably looking to get the best return for the investment when purchasing equipment for their sanctuary. But to choose wisely, one should understand what LED features are needed for reliable use over the long haul. Hopefully, this article has laid out some of the areas to assess when considering cheaper fixtures over more expensive alternatives. Cheaper purchases don't necessarily mean that they will cost you less than more expensive alternatives in the long run.
This article was first published in the March-April 2019 edition of Worship AVL. Subscribe at www.proavl-central.com/subscribe/worship