Lighting Ud

Voltage  fluctuation can be a problem. Probably not so bad now everything is led. 

I’ll add to that question, is the 3% requirement for lighting circuits still relevant?

Still somewhat relevant as there is still incandescent lighting being installed, including halogen what is a sub-species of incandescent.

Voltage drop on lighting circuits significantly reduces the already low efficiency of incandescent lamps. Also lamp flicker caused by voltage variations is obtrusive and displeasing.

A lot of LED driver designs can adapt slowly to changing mains levels over a wide range but seem to be remarkably prone to flicker from fast transients - a sort of ‘worst of all worlds’ situation. I certainly  seem to see more flicker on LED lights than traditional lamps.

Mike.

I sit here under a couple of LED lamps, which are rock steady although they weren't a few months ago. When I went through my check-box routine earlier, we were on 238 V.

My LED head torch works far better on a low voltage than an incandescent lamp, but does get steadily dimmer with useful light going at about 1.15 V per cell.

So my inclination is that LED luminaires could cope perfectly well with a 10%, if not 20% VD.

Whilst many modern types of LED driver circuit will accept a wide range of in put voltage, that is not the only factor to consider.

Voltage drop represents energy paid for but not serving any useful purpose. At a time of increasing energy costs and growing environmental concerns we should be seeking to reduce voltage drop, not looking for ways to justify greater losses.

Consider for example a lighting circuit in a shop with a load of 1000 watts and voltage drop of 5%. That represents a loss of 50 watts. If the lighting is used for 4,000 hours a year then 200 kwh is wasted a year.

200 kwh a year is likely to cost at least £50 a year or £500 over a conservative 10 year life of the installation. Reducing this waste from 5% down to 2.5% could therefore save £250 PER CIRCUIT over an estimated 10 year life. Larger cable starts to look like a wise investment.

Obviously more copper involved with lower voltage drops and fair point about energy saving. Energy saving was not what I was taught with circuit design but material costs were upmost. More money to be made by energy providers with higher allowable volt drops. Now energy is becoming scarce due to government environmental policy, voltage drops may change again. However, there may be a copper shortage once the green madness really kicks in with heat pumps, ev's and hydrogen production.

I was in an office a couple of weeks ago which was lit by  those 4 tube flu light units  i think was 4 x 2 foot tubes but not sure also in the middle of the ceiling was a LED lamp one of those large square ones anyhow I noticed that around twice a minute the light would flicker momentarily  then after that have a noticeable 50 or 100 cycle flicker which would quickly go away only to be repeated a short while later. I'm not sure if this is a supply issue or just a cheap crappy lighting unit  i find it difficult to believe it's the supply as the office is right next to the substation. Either way if volt drop is the issue it needs some careful thought if they eventually replace all the flu lamps with LED 

Was the office in the City of London ? If so then public lighting is often controlled by the Thorn cyclocontrol system.

This uses equipment located in the DNO substations that imposes coded pulse signals on the mains.

Public lighting is controlled by a receiver that detects these signals and switches the lamps. This has advantages over the more commonly used photocells.

All lights can be turned in daylight to test them.

All lights can be turned of at night to facilitate filming.

Street signs, Christmas lighting, and illuminated road signs may be separatly controlled.

Half lighting for part of the night may be selected.

Operation unaffected by tall buildings shading the photocells or by extraneous lighting falling thereon. This is of particular importance in the City, where by long tradition the street lights are affixed to buildings and not supported on posts or columns.

These pulses have considerable energy and can produce noticeable lamp flicker. The equipment can absorb 100 kw, though only for a fraction of a second.