The words lighting flicker alone bring on a headache. Of course we all have visions of a dodgy fluorescent lamp in a ceiling dying a slow death of low frequency cycling. However it is avoidable – it is not inherent in all artificial lighting – and with a little knowledge you can manage the problem.
5 things you need to know about lighting flicker
1. All lighting flickers.
You do not need to be an electrician to get this bit – an AC power supply that we all use modulates usually to a frequency of 50 or 60 hz or double mains frequency. This causes the source of the light to turn on and turn off at this rate – fast enough to appear visually smooth.
2. Discernable flicker can be detrimental to health
According to studies a low proportion of humans are susceptible to flashing lights which can trigger ailments and seizures but lesser known is that long term exposure to unintentional flickering of 70 to 160 hz can cause visual impairment and migraines. Research has shown the retina in the eye can pick up frequencies of 100 to 150hz unbeknown to us, potentially a contributing factor to ‘sick building syndrome’ – offices that for a number of factors see a high propensity of illness.
3. Is LED more prone to flicker than other traditional sources?
An important question with a complicated answer, as LED lighting can be powered in various ways – e.g. with constant current and constant voltage drivers, and without drivers with direct AC power. BUT what we want to know is if it’s safe to use? The fact that solid state LEDs are a fast cycle technology and effective at being completely on and then completely off – so this will increase the sense of flicker unless handled. Traditional sources such as tungsten even when on the OFF cycle still emit some light, creating a smoother light. This is where a good LED driver has a job to do to minimise this effect.
4. Does dimming increase the sensation of obstructive flicker?
It depends on how the dimming is done but yes it can.
a) Dimming a light can be done by reducing the amount of power it receives.
This is done by chopping off some of the AC cycle of power – creating a wider gap between ON and OFF which can begin to be seen by the eye unless dealt with by the correct type of dimmer module. So without good compatibility between dimmer and light – flicker will occur.
b) Dimming an LED can be done by Pulse Width Modulation – like a TV screen that flashes many frames per second giving the eye a smooth transitional between each frame, i.e. it’s too fast to discern. By turning the power on and off fast enough, less power is used so the light is dimmed – but if not fast enough strobing will be apparent.
5. There is no national standard defining what rate of flicker is unacceptable.
In the absence of a universally definable level of noticeable flicker, it does feel we are exposed to making mistakes when specifying. At Orange lighting our approach is to buy and deliver the best quality LED driver whenever we can – on all projects, sourcing from manufacturers who have given this issue consideration.