Moonlight Night Light

[Hysteresis]

Has anyone got any thoughts on These Night Lights they have been around for quite a few years so
I have purchased a Moonlight and was very impressed with it's light output, however I decided to check the claims of the light with respect to 4.38 kWh per year if used continuously for 24 hours per day 365 days per year.
See http://www.ecohamster.co.uk/product...cts_id=8662&osCsid=b8q73kmkreosvvfs0ah20kkv04
I measured the current drawn by the Moonlight on 240v and found it to be 23.8mA, this equates to 5.7W, assuming unity Power Factor. Now, if the light is used for 24 hours per day for 365 days (ie 8760 hours), would result in a power consumption of 50kWh. which is in fact over 11 times that which is claimed.
In order to check my test instruments which was a Digital ammeter, I inserted a 9W bulb into the circuit and my test instruments confirmed a current of 37mA which is correct, As a further check I used a 25 Watt incandescent bulb and again recorded a current of 104mA. This being correct, it confirms the calibration of my instruments.
For the claim of 4.38kWh to be correct, the power consumption of the Moonlight should be 0.5W and as such the Moonlight should only draw 2mA, infact it draws over 11 times this at 23.8mA.
These calculations are assuming, as stated, a unity Power Factor. In order to achieve the power consumption claimed, the power factor will need to be around 0.1, suggesting that the lights are almost totally Capacative.
Any comments anyone - not sure whether this post should be on General DIY or General Discussion, if I get no repsonce here I will try the other Forums.

 

[breezer]

why not show your "evidence" to the makers?

the link clearly says

The night light will run 24 hours a day for 365 days a year for under 50 pence.


all they have to do is say the cost of lecy went up

 

[BS3036]

As a matter of interest - do the instructions give a manufacturers website? I can only find distributors. Certainly some of them quote actual power, so it can't be a misunderstanding about the price of electricity.

I wonder if the current draw waveform gives deceptive results on a meter. I think you'd have to double check with some form of oscilloscope and series resistor to be really sure.

 

[Hysteresis]

Hi Breezer,
Thanks for your comments. I have sent the test results to the Distributor in the hope that they have details of the manufacturer, as the web site and the packaging in which the unit was delivered does not give any details of the Manufacturer. Also the cost of 50p per year is dependant on electricity cost but the manufacturers details say the energy consumption is 4.38 kWh per year when used 24 hrs per day 365 days per year this equating therefore to 0.5 watts. My current measurement suggests this to be 5.7 watts assuming unity Power Factor. A factor of over 11 higher.
Hi BS3036,
Thanks for your interest. I agree the waveform or more likely power factor will effect the apparent power/current(RMS) value. I would have a look at a 'scope but I unfortunately do not have access to one. (I am a retired Chartered Elec Engineer). Although I have written to the distributer as I don't know the manufacturer, all they have said is that millions of these things have been sold worldwide and therefore the claims Must be true. Maybe I am a sceptical old b*****d, and the answer may be that the units have a high capacative reactance, but without a 'scope or a calibrated wattmeter I am stumped. I can't practically use the domestic meter as even if it were 5 watts power consumption I would have to have all other power in the house isolated and the light left on for a few days for the meter to detect it and for obvious reasons this is not practical. If I had contacts with the local University or colleges I could try their equipment but unfortunately I don't.
I took a long shot in the hope that someone on DIYnot had done some checks on this unit, but I must admit it is a long shot.

 

[Adam_151]

I'd say its highly likely that its mostly a capacitive load... well at least it would be if I were designing it

Anyway, have you considered on of those plug in consumption meteres from the likes of maplin?

And have you considered pulling it apa and drawing a schematic diagram?

 

[Hysteresis]

I'd say its highly likely that its mostly a capacitive load... well at least it would be if I were designing it

Anyway, have you considered on of those plug in consumption meteres from the likes of maplin?

And have you considered pulling it apa and drawing a schematic diagram?

Hi Adam,
I did consider a consumptiom meter but at a round £20, it rather defeated the cost saving objectives of the device in the first place. Pulling it apart is not really practical as it is a sealed unit and I would probably distroy it in the process. I think maybe a schematic diagram would be useful although not entirely difinitive as I think the light generator is not of the flourescent or incandescent form and as such I don't know whathow the light generator operates in a physical sence.
I think probably the only practical way to determine the energy consumption will be as you suggest, that being a power device albeit more expensive than the unit itself.
Thanks for your interest.

 

[hairyben]

While your calcs may be out due to PF, they won't be that far out, probably a %. But you're an engineer so I suspect you already know that.

Green is an "in-fad", to some a religion. So of course we need products to pander to peoples weakness and desires.

The fact they don't is irrelevant- 99% of people will be blissfully ignorant...

 

[blondini]

Looks like the light scource is an electroluminescent panel, I had to dig deep into the memory banks for that one.
Looked it up and found a reference that said they have

Very low leading power factor. A large installation would require a sizeable choke for p.f. correction

 

[plugwash]

While your calcs may be out due to PF, they won't be that far out,

That depends on just how low the power factor is. A power factor of 0.1 is perfectly plausible.

 

[blondini]

... the answer may be that the units have a high capacative reactance...

As I said earlier it looks like an electroluminescent panel and from further reading on electroluminescent devices, they do appear to have a high capacitive reactance.

 

[Hysteresis]

While your calcs may be out due to PF, they won't be that far out, probably a %. ...

Not so Hairyben. W = VIcos(phi) and cos (phi) can be zero in a purely reactive load.

 

[Hysteresis]

Hi Blondini and plugwash,
I have no textbook on electroluminescence so the mighty Google came to the rescue. The device is as you say highly capacitive and as such will have a very low power factor and will probably be in the area of 0.1 which will account for my results.
I have contacted the distributors and they have kindly carried out an initial test with a power meter and they confirmed that the power consumption was under 1Watt which was the lowest resolution of their meter. They are now going to do further tests with several other lower resolution power meters to confirm the results.
I have got to admit to the fact that I have never studied electroluminescence formally but the information from my google search has enlightened my ignorance.
Thanks for you help and interest.

 

[tim west]

Trouble with current technology EL panels have a limited lifespan and their light output will fall as it ages with use, EL wire is great fun to use though

http://www.elbestbuy.com/?gclid=CLWQ8L7ziJcCFQ4i3god6j6pDA

 

[hairyben]

While your calcs may be out due to PF, they won't be that far out, probably a %. ...

Not so Hairyben. W = VIcos(phi) and cos (phi) can be zero in a purely reactive load.

Okay looks like I'm wrong

I thought such out of phase pf was designed out or compensated for in consumer products, guess it's just not bothered with for something that uses so little power.

 

[Hysteresis]

Fair Comment Hairyben. Power Factor correction is employed industrially, but if these devices were corrected the load taken by the Inductance to PF correct would probably deteat the object of the low power consuption of the unit. The low power consumption is negligable but if 20 million houses had a couple of them then the power factor would become significant.
Not really thought about it but I am sure the Elect Distribution companies would be not too happy with it as it would constitute something like 20 MVAr.