"Sengled Everbright" backup battery LED bulb

[ozcar]

Not sure if a device like this has been covered before here - I couldn't turn anything up, at least not with the Sengled brand name.

A few weeks ago I heard about a LED light bulb with a backup battery in it. Yesterday I went to the local hardware store, and lo and behold, they happened to be selling the exact things for half price. You guessed it, I bought one. I have seen various lights that charge on the mains, but this one is different to anything I have encounter before.

This is what it is like https://us.sengled.com/products/sengled-led-with-battery-back-up-a19-bulb

The one I got is a bayonet fitting and rated for 220-240V, and it looks pretty much like a normal LED bulb, perhaps a teeny bit longer, and definitely a lot heavier.

This is what they say about it on that site: "Everbright automatically switches on when the power goes out but can be turned on and off as normal during a power outage." That sounds pretty normal, but there are no switches or buttons on it, so how do you turn it on and off when the power is out? Well, you just use the normal wall switch, or for my test, a switch on the power board that I plugged a desk lamp holder into!

If you look at the reviews on the site linked to above, some buyers tried to test that the bulbs would come on if the power fails, and one returned his one when it failed this test. Another tried every possible way he could think of to simulate a power failure, but never succeeded - he was then told that the lamp was smart enough to be able to know a real power failure from a test!

I found I could get it to work as advertised, by turning off the circuit it was plugged into at the switchboard. In this state, yes, it could be turned on and off as if the power was still on, using the switch on the power board, or using the switch on the outlet that the power board was plugged into. I also found, that when the power was out, and the bulb was turned on, removing it from the socket caused it to turn off. Another observation is that whenever you turn it on or off, there is a slight delay before it responds.

I tried another test, where I plugged the desk lamp holder into a long extension cord, around 30 meters worth, and no, in this situation I could not trick it into believing the power was off.

There is a panel on the side of the bulb that looks like it could slide out, but it appears to be held in place with a pin or screw, and I have not tried to prise it out.

I found that there is around 1.7VDC across the pins on the bulb when it is unplugged. I also discovered that connecting a 390K resistor across the pins causes it to turn on.

Whatever it is doing, it does not seem to be perfect. One reviewer on that site returned his one when he found that he could not turn it off.

So, what black magic is employed? How does it tell the difference between the power being turned of by the normal or "intended" switch, from losing power due to a tree falling on the power line down the street (of the power being cut at the switchboard)?

[David_AVD]

Sounds like the type of circuitry that was in an exit light fitting that Big Clive tore down a couple of months ago.  Check his video channel as I think he drew out the schematic.

[ozcar]

I had a look at the exit sign video, but I can't see much similarity, other than both have a backup battery and some LEDs.

The exit sign does not have to be controlled by an external switch, and somehow be able to detect when that switch is closed, even when the mains power has failed.

I'll look at the bulb a bit more when I get the chance.

[David_AVD]

I think there's more than one exit sign video, but I was pretty sure it mentioned how the mains fail was detected.  Basically it's just looking for leakage across the mains terminals from other devices on the power and/or lighting circuit.  When it see that it knows the actual light switch is closed, but there is no mains voltage.

[tsman]

It works how David_AVD said. The Sengled casing does looks nicer and has a couple switches as well.

[ozcar]

Meanwhile, I tried a few more things, and figured out how it works myself. I'll take a look at the other video later.

I'm not surprised that some purchasers were confused, because depending on the situation it could behave in strange ways. For example, if connected to a circuit with other "ordinary" lamps on it, controlled by the same switch, you have the problem that one of the reviewers had - where it is impossible to turn the thing off. Or, if there are other things on the circuit, each with their own switches, then turning the last one of those off will make the magic bulb go off too.

I found it was a bit finicky about the load on the circuit too. In one test I has a bench drill as the only other load, and the bulb was turning on and off every few seconds.

I think it is a useful thing to have but you definitely need to know its foibles.

BTW, this Sengled has no switches on it, but I see another one on their web site which does have switches on it.

[amyk]

Big Clive has a few other videos on this type of bulb:

[ozcar]

Thanks, this sort of lamp seems to be quite common, but I had not encountered one before.

I heard about this Sengled one from an electrician, who was particularly taken by the ability to turn the thing on and off when the power was out. He obviously did not know how it actually works, and I guess had not encountered the situations where that feature might not work as expected.

I tried searching for information about them, and all I turned up was those reviews where people report mixed success with the advertised feature of being always able to turn them on and off from the wall switch. I did not try to include the word "emergency" when searching, nor did I think to look specifically for anything by Big Clive.