LEDs are replacing conventional fluorescent lighting in many areas, but in the view of Phil Myles, Solite Europe, cleanroom managers should make sure to read the small print, as there is more to cleanroom lighting than meets the eye.
Lighting designers can sometimes get a little emotional where clean areas are concerned. Generally a sensitive lot, we often have a tendency to feel taken for granted, you hit the switch, and on comes the light. Nothing to get too excited about. Except of course when the lights don’t come on. The complete absence of any natural light in the typical cleanroom creates total darkness. Who’s important now?
All that is starting to change, however. We are at the beginning of a revolution in how we provide artificial light in our working environments thanks to the developing potential of LED light sources. At last, something to get excited about.
If you believe all the hype, LED lighting can offer attractive energy savings and impressive operational life survival. As routine maintenance often requires disruption to the processes in the environment to allow service engineers to replace fluorescent lamps, any potential for extending maintenance cycles, such as longer light source survival, has the potential to provide real savings.
So what are the facts? There are two key areas to investigate when considering LED over fluorescent:
- What is the real energy saving opportunity?
- What are the in-service life performance comparisons? – i.e. lumen output, maintenance, and how long will they last before needing to be replaced?
First, it is vital that we start by comparing like for like. Often projected savings compare old fluorescent performance data such as T8 for lamps with “optimised” LED alternatives on refurbishment projects. The facts are that modern high efficiency T5 fluorescent lamps are very close to optimised LED outputs, and in some cases better when making comparisons for new build designs.
For example, a single 80 CRI power LED driven at 350mA will create around 98 “hot” lumens and consume 1 watt of electricity (98 lumens/watt). A 28W T5 fluorescent lamp will provide 2,600 lumens, thereby achieving 92.8 lumens/watt. A modest reduction, but we are not quite saving the planet.
Beware: LED manufacturers often quote higher lumen performance but do not highlight lower CRI (colour rendering characteristics) – a vital factor for lighting applications in clean areas where visual acuity and accurate colour representation are critical.
It is also vital to consider the thermal management of the LED to realise its full lumen output potential. Unlike a fluorescent tube, which releases heat by radiation in 360 degrees, an LED requires excellent contact with a heat sink to dissipate its generated heat by conduction in the opposite direction to its emitted light.
The lumen output and service life survival reduce dramatically if LEDs are not supported by a high quality, well designed, thermally managed platform. Therefore, beware of low quality LEDs that are flooding the market; the adage “if its cheap, there’s usually a reason” is very appropriate.
The energy saving argument therefore is not stunning at the moment. LED technology is progressing rapidly – in fact so quickly that it is difficult to make meaningful comparisons with current fluorescent lamp performance, which is also continuously developing.
If we assume that we are providing an excellently thermally managed LED platform with quality components throughout, we can then consider the benefits of longer service life. LED manufacturers are currently rating survival periods of 50,000 to 60,000 hours. If we assume a cleanroom facility is in operation 24 hours a day for 365 days a year (worst-case scenario), then in theory, the LEDs should last for six years before requiring maintenance by replacement. The lumen performance data provided by LED manufacturers advises that over this period each LED could lose up to 30% of its usable light.
By direct comparison, a high quality T5 fluorescent tube has a survival rating of 30,000 hours and will lose up to 10% of its lumen output. The lighting designer will also have to factor in an assumption that 50% of the lamps in an installation could have failed by the end of this period. Therefore, it is usual to recommend that fluorescent lamp replacement should be considered as part of the routine maintenance cycle after 12,000 to 15,000 hours (typically on a two-year cycle).
As is always the case, the devil is in the detail. The lighting designer should consider these issues when applying a maintenance factor to the lighting calculations for any proposal.
The biggest single drawback when considering LED is cost. If quality products are used to guarantee the potential benefits in service survival, then it can be assumed that the luminaire price will be approximately double (or even more) the cost of its equivalent fluorescent offer for lighting large internal areas typical of modern cleanrooms.
The critical nature of typical cleanroom processes requires the highest quality and consistency of features, such as colour rendering (CRI) and colour temperature. It is often the case that other lighting applications have less stringent demands – a point to remember when hanging up those flashing LED Christmas tree lights.
However, if the benefits of extending routine maintenance cycles – negating the need for disruption to room processes – are paramount, then the investment in LED can be attractive and the technology is available now.
A final word on energy saving. If a company really wants to make an impact on its energy demand, then integrating lighting controls to each luminaire should be considered. By each luminaire sensing its local environment and dimming to provide the required lighting level, over-lighting is avoided and energy is saved. Presence or absence detection can switch lights off in unoccupied areas and can be utilised to remove the need for manual switching.
Across a large installation the savings add up and potential payback can be calculated to justify the investment. If natural light from windows can be harvested, daylight-linked dimming can make a further dramatic saving.
There is certainly a lot more to lighting than meets the eye.
