Switching over from HID lighting technologies to modern solid state LED lighting.

April 21, 2017

 

Welcome to this blog, which looks at the potential perils of switching over from HID lighting technologies to modern solid state LED lighting.

 

It is a commonly made [but incorrect] assumption, that solid state/LED based lighting products should be as robust as old magnetic/HID lighting products. Many of us have heard stories of old magnetic HID lamps catching fire on sites– and still operating [even afterwards], this is a good example of how robust HID gear can be with regards to Ta limits! – Obviously modern LED luminaire’s contain plastic [in their LEDs casing] so would not survive such treatment- But, there are also other equally important differences to be considered.

 

We advise users to make sure they know what the limitations of solid state/LED based luminaires are -when replacing nearly indestructible magnetic gear on sites which may have environmental and power quality issues which have not been tested in use with solid state lighting before.  

 

Old magnetic control gear technologies [such as HID/fluorescent] are well known for their ability to handle harsh industrial environments- such as sites where the following issues may occur:

 

  • Surge and interruptions.

  • Fast transient voltage spikes.

  • Excessive current harmonics from heavy machinery [such as motors/arc furnaces /resonating HIDs].

  • Onsite voltage distortion [caused by heavy machinery]

  • Excessive current through a neutral line [caused by harmonics] with poor earth bonding- leading to a raised voltage on the neutral [with high voltage harmonic levels]

  • Imbalanced three phase supplies

  • High onsite temperatures [possibly combined with power quality issues that also increases internal generated heat in the luminaire] 

  • Lack of access to light fittings in dirty/dusty environments- where luminaire cleaning/servicing is not performed. [Possibly combined with the previous point above]

  • Sites that use/emit organic solvents/chlorine/dust/liquids/materials that can thermally insulate fittings –especially if they are not regularly cleaned.  

Very important note:

 

It is of vital importance to know what the limitations/differences of the new LED lighting products are with regards to replacing HID based lighting on site with any of the issues above.

 

To blindly assume that new solid state LED gear will identically match the robustness of magnetic gear in the same environment is to court disaster.

 

We know for example, that introducing triac based dimming on a noisy AC supply on a heavy industrial site [with ringing affect/current harmonics from HID gear+ harmonics from motors/heavy machinery] would be bad choice, as solid state triac dimmers are more very prone to onsite EMC issues as opposed to old magnetic control gear -the result would be an unstable dimming control with flicker issues. -likewise, when looking to using technologies other than magnetic based control gear on sites with heavy machinery -such as SELV driven LED or AC direct driver LED, we would also consider onsite power quality issues that could affect the particular designs/types of LED products available. It is wise- not to assume, that all LED products us the same design –with the same specification /environment handling [even products using the same driver/LED can differ in thermal performance and EMC]    

 

EMC

 

It should be noted that modern solid state lighting products are rated as C class [ under BSEN 61000-3-2 Limits for harmonic current emissions using less than 16A per phase] -this specifies the allowed amount of current harmonics/voltage distortion the product will emit, and also the allowed degree of voltage distortion the product will happily operate from.

 

Heavy site machinery, including arc furnaces/large motors create a much higher level of current/voltage harmonics than found in class 1or class 2 pollution environments and can damage class C equipment, if the low voltage power line to the class C equipment is not is not filtered/corrected with regards to harmonic levels being non-compliant to the limitations set by BSEN50160.

 

One common old site issue, is high excessive neutral currents [ + if earth bonding is poor and the neutral current harmonic level is very high with a noisy voltage present on the neutral ]  in such cases ,the rectifier stages of solid state control gear/LED drivers can be switched on/off rapidly by heavy voltage distortion [HF noise]. This creates additional diode inrush currents and also switching noise into the driver- the high level of injected noise into the driver’s rectified DC supply can on some designs -cause interference with the driver’s oscillator stage [affecting output current stability/flicker]. On other designs it could lead to overheating of the HF filter stage on the AC input of the driver.

 

The result is the driver’s rectifier diodes/AC filter are working harder [more often- increasing heat/reducing driver lifespan] The additional internally generated heat will lower the Ta rating of the luminaire and possibly reduce the LEDs lifespan and L70 performed capability, Note: such heavy industrial sites may have high onsite ambient temperatures and dust levels [ also the luminaires heatsinks may be rarely cleaned ] so a lowering of the luminaires Ta could prove to be catastrophic, the site may think the luminaires failed purely because of temperature issues and not identify the voltage distortion as the main contributing cause.  

 

Many solid state driven fluorescent luminaires may have great difficulty striking up when wired in parallel to a resonating HID lamp or high voltage harmonics from heavy machinery - due to interference of the drivers start-up sequence caused by voltage harmonics/interruptions or low voltage levels, in such cases repetitive failed attempts to strike fluorescent tubes during periods of high onsite harmonics can eventually overheat/wear down/blow the luminaires output semiconductors. 

 

Important note:

 

Some solid state drivers employ power factor correction circuity- which senses and adjusts the drivers current consumption dynamically- depending on the phase position of the incoming AC wave- however, if there are high voltage distortion levels present, the correction circuit cannot sense the AC waves phase position correctly– so the drivers power factor sensing is thrown out ,possibly leading to even more voltage onsite distortion –complicating the situation further [depending on make design of driver]

 

On LED drivers with very low power factors [0.5] – the timing /phase angle of the current flow will be corrupted by onsite voltage distortion- depending on design, this may affect light output stability/power consumption and could cause PWM flickering, as well as a possible breach of current harmonic emissions from the luminaire. 

                    

In the past, older robust HID control gear was often used on sites with high harmonic levels [without too many issues other than flickering and occasionally bursting into flames] unlike solid state gear, the old magnetic transformers do not immediately fail through overheating/overvoltage- as mentioned before they can even work when on fire, as they do not have the same thermal protection safety features!

 

It is worth noting that resonating HID control gear can cause voltage distortion/interruptions that can cause flicker on the HID lamps [ and other parallel lighting] Most modern LED fittings are designed to be mainly flicker free , so when wired in parallel with such resonating HID units ,the LED driver may experience rapid on/off switching/inrushes -while the LED lamps internal electrolytic capacitors will be working harder to reduce flicker -decreasing capacitor lifespan and introducing additional internal heat, thus lowering the LED products Ta rating.   

 

All Class C lighting equipment is intended/designed for use on onsite supplies that are compliant to the limitations described in BSEN50160 this standard [as used by all good power quality loggers] provides a set of parameters/limitations which are commonly expected on industrial sites – when voltage or current harmonic levels exceed these stated limitations – we would also expect to see performance problems with other onsite solid state equipment such as computers/audio equipment.     

 

Other important differences between HID and LED luminaires-

 

Vitally important note: Dust handling /Cleaning schedule

 

In comparison, a typical LED luminaire employs a heatsink, and just like any other heatsink – if it is covered in dust/dirt it will cease to cool down the LEDs/driver and they will overheat/fail – on all solid state based products it is vital to keep the heatsink working/clean, otherwise the luminaire could thermally cut-out, or derate [derating is where the light output is reduced to avoid driver overheating] or fail to meet L70 performance requirements.

 

One long term result of non-serviced heatsinks –could be luminaire output derating, which could cause onsite safety issues with regards to acceptable lighting levels and can lead to a legal dispute.