Monthly Archives: September 2020

Contrasts in Smart Lighting

We recently enjoyed a week’s holiday at Pevensey Bay. The home that we rented, like our own, includes many smart features but there are some similarities and differences in approach. One area of difference in smart lighting.

The Studio, Pevensey Bay

Both our own home and The Studio have smart lighting but differ in approach. Our own smart lighting concentrates on smart bulbs, while The Studio (with the exception of the kitchen) concentrates on smart switches. So why choose one approach over the other?

At our home we have a handful of smart bulbs, with standard dumb switches. The bulbs incorporate functions like dusk-to-dawn lighting and colour change for status indication (open windows, movement in garage etc). At The Studio there are a large number of smart switches controlling an even larger number of standard dumb bulbs.

So let’s think about choices:

Cost.

If you are going to control multiple bulbs together on one circuit then it’s generally cheaper to have one smart switch than multiple smart bulbs.

4 gang Lightwave switch

Coloured smart bulb

Colour.

Smart switches can either control on/off or act as dimmers, but they don’t vary colour. Some smart bulbs can vary colour. If you want to control colour then you’re going to need some sort of remote control (like The Studio in the kitchen) or access via smart device like a phone or tablet.

Wiring.

Most smart light switches require a neutral wire. However many UK homes do NOT provide a neutral wire at the switch. A typical UK light switch has a live, switched live and earth only (I.e. no neutral) although there may be confusion as the switched live is commonly blue (or black in older homes) like a neutral would be.

Adding a neutral can be relatively costly as it requires a new cable between the ceiling rose and the switch. If having a re-wire it’s worth adding neutrals to the specification just in case.

Typical ceiling rose wiring UK.
Example automation

Automation.

Both switches or bulbs can be automated via a smart hub for on/off or brightness to respond to time-of-day, movement, door or window opening etc; so that’s not really grounds to chose between smart switches or smart bulbs.

What about combining smart switches and bulbs on the same circuit?

In short I don’t really know why you’d want to. Even if it worked properly you’d have incurred extra cost for the second smart device for limited benefit as you’ve duplicated the smart functions, but it’s likely not to work properly. Even with simple on/off functions the smart bulb will be missed by the hub when the power is off at the switch (although some ecosystems allow this error to be masked), but with dimmers it will probably be worse as the bulb may not function correctly when the dimmer is set to less than 100% brightness.

You might consider using the smart switch as an smart button without using the switched output, and feed the smart bulb from a permanent live, but that’s not combining them on the same circuit. This could be achieved physically by something as simple as moving the switched live output to the live input on a switch. However the two smart devices, switch and bulb, would then need to be linked entirely programmatically through the hub. That would be at least two automations in HomeKIt – an ‘on’ automation and an ‘off’ automation.

Conclusion

There isn’t a right answer whether smart switches or smart bulbs are best. The best choice will depend on your situation.

Inducted into the hall of fame

One of the features of our home is the all-electric kitchen. We do have gas for space heating and as a back-up on the hot water for days that are both dull and have relatively high cost electricity, but the kitchen is all-electric. I have to say that this was not our choice, rather the kitchen came that way when we bought the house five years ago. We have replaced the oven in the meantime, but until today the hob was that bought with the house.

Unfortunately the hob suffered a failure of the two of the rings and today we’ve replaced it like-for-like with a new inductive unit. Inductive is attractive as it’s relatively efficient, but I was struck by the fact that the one hob required a 32 Amp supply, but the new one manages with a 13 Amp plug.

Bosch PUE611BF1B inductive hob.

So, by what magic does the new hob use less than half the power of its predecessor?

itemold hobNew hob
Smallest ring1,200 Watts1,400 Watts
Second smallest 1,400 Watts1,800 Watts
Second largest1,800 Watts1,800 Watts
Largest ring2,200 Watts2,200 Watts
Total *6,600 Watts3,000 Watts
Tabulated of maximum non-Boost power per ring with manufacturer’s total

The first thing to observe is that the sum of the ring powers does not equal the manufacturer’s total for the new hob, although it does for the old hob. The second would be that the sum of the new ring powers at 7,200 Watts is more than the sum of the old ring powers even though the required total is less!

The answer is that the new hob features power management capability. In any hob the rings will spend much of their time cycling on and off to maintain the required heat. In the old hob all the rings might on at one time drawing maximum power, but a few moments later they might all be off. However the power management in the new hob the total power would be levelled out so that the average over time might be the same, but the peaks smaller and the troughs shallower.

For most people this levelling out of the power demand would pass unnoticed, but for us it could be quite useful.

We do most of our cooking in the evenings for which, particularly in winter, power is taken from our Powervault storage battery with any excess from the grid as illustrated by the series of evening spikes in the image to the right. The Powervault has a relatively limited maximum power (hence the spikes) but as the new hob has power management then any spiking beyond battery maximum power capability should be reduced thus avoiding what, for us, could be peak rate electricity at 35 p/kWh on our dynamic smart tariff which is a direct cost save.