led lighting

the watchman

Hi All,
Hope I'm in the right place.
I just bought one of those table lamps using LED technology. 21 white leds.
I know that the power consumption is very low but I'm just curious as to how low it actually is. Could someone tell me in terms of Watts, something I understand, 60watt light bulb and all that! what it is. I'm guessing it might be below 1 Watt because there is no reference to Wattage on the packaging or instructions.

Thanks for reading.

Antar Bolaeisk

This is pure guestimation but if I remember correctly a typical high power white LED requires about 3V and draws about 30mA which would put power consumption for 21 LEDs at approximately 2W (unless I've made a mistake or bad assumption)

Of course I'd need proper current draw and voltage to tell you how much it does use and there would also be inefficiencies in the transformer which would result in a higher power consumption. I find it strange that nowhere does it state the power consumption.

the watchman

Thanks for that Antar. Since I last posted I managed to find an equation chart on net so will have a go at working it out in a minute.

I found this in lamp packaging
In the instruction leaflet it read:
input 230-240v transformer
output 12v----150mA, which meant nothing to me at the time.

I'm not sure if I've got this right but if the150mA is the total for lamp then 12x ...no, I'm lost !!!lol.

So its over to you Antar please.......

Antar Bolaeisk

Power usage is basically just the current times the voltage and you get a value in Watts.

So in this case it's 12V x .15A which is 1.8W

My guestimate wasn't too bad after all and it'll probably be slightly higher due to inefficiencies in the transformer stepping down the voltage (the most obvious of these inefficiencies is the production of heat).

the watchman

Thank you Antar. your very good. It was that decimal point (.15A)that threw me off. Its been a while since the days I had to do those sums on regular basis.
I am very pleased with that result. To my mind at that rate the power usage is negligible. Also you can barely feel any warmth at all from the transformer or from the LEDS for that matter. I'm guessing it hardly goes beyond the 2 watts. Well thats my bit done for the planet, I think I can go and turn the heat up and leave everything thing on stand-by for a month now without feeling guilty lol:D.

Thanks again most appreciated.

Ps. Whilst looking on net for LED info I came across this article. It surprised me that some modern large flatscreen Tvs use more power than the old CRT tvs. Have attached doc for anyone interested in this.:pac:

Antar Bolaeisk

You're welcome.

Skerries

so does that mean that 10 leds is roughly equal to a watt?