# LED light: 120V and 25watts vs 12Volts and 25 watts: whats the difference?

#### kamas

Mar 29, 2018
2
I am trying to understand the difference between these two. They are LED lights that come on a strip, about 3 feet long.

One of them has these specifications: 120 Volts, 25 Watts

The other one has these specifications: 12 Volts, 25 Watts

So, what is the difference between them? do they both use the same exact amount of power? Why is there such a HUGE difference in voltage? Are there any advantages or disadvantages between the two?

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,890
It is really hard to compare the two LED strings when you don't provide ANY information other than power and voltage requirements and the length of the strip. Post links to each of the two products and upload pictures and manufacturer's suggested wiring diagrams. Don't make us jump through your monitor screen and pull your teeth to obtain this information!

LEDs require DC voltage, not AC voltage, to operate. The amount of voltage required depends on how the LEDs are connected and the number of LEDs illuminated.

If one strip provides for operation from 120 V AC line voltage, then there is additional circuitry involved to rectify and reduce the line voltage and limit the current to levels appropriate for LED operation. You didn't specify whether the 120 Volts was AC or DC.

If another strip provides for operation from 12 V DC (a car battery for example), additional circuitry is involved to reduce the voltage and limit the current to levels appropriate for LED operation. You didn't specify whether the 12 Volts was AC or DC.

While both LED strips may consume the same amount of nominal power, or 25 watts in this case, they will have very different additional circuitry. Sometimes the additional circuitry is "built in" to the LED strip and sometimes it is external to the strip. Sometimes it is both. For example, consider the case of a "wall wart" that plugs into a 120 V AC convenience outlet and connects to the LED strip.

Most LED strips are manufactured with two DC power supply rails that run the length of the strip, one on each side. The power rails connect to integrated circuit LED current drivers interspersed between groups of two, three, or four LED emitters. This is repeated throughout the entire length of the strip, which may originally have been several hundred meters long before being cut to "three-foot lengths" or some other appropriate length. The advantage of this is economy-of-scale and a fixed power consumption per unit of length. There are many variations on this theme, such as RGB LEDs and color controlled LED strips.

Tell us what you have, @kamas, and maybe we can tell you what the difference is between your "125 Volt, 25 watt" strip and your "12 V, 25 watt" strip.

#### kamas

Mar 29, 2018
2
ok thank you! I think I understand now. one of them is on AC , but that means its got circuits inside to control it.
The other one is also on AC, but it first connects to a "DC converter" box that makes it 12 volts.

#### Tha fios agaibh

Aug 11, 2014
2,253
Good explanation @hevans1944, but I think @kamas may not be clear on some definitions.

To put it another simple way;
Watts is the power consumed by the light circuit, not the power available at the source.
The voltage choices given are for the convenience of what circuit you plan to hook it up to.

At different voltages the amount of current (amps) used will be different, but the same wattage is consumed either way.

Ohms law tells us Current (Amps)=Watts/Volts. Or,
25watts /120v =.208amps
25watts /12v=2.08amps

At 12volts, more current is drawn, but the Power consumed is the same (25w) at both voltages.

#### kellys_eye

Jun 25, 2010
6,514
Agreed.

The issue is ENERGY, not 'volts' or 'amps' but energy (as measured in watts) is the product of the volts and the amps.

#### BobK

Jan 5, 2010
7,682
Energy is not measured in Watts.

Change "energy" to "power" in the above post.

Bob

#### Audioguru

Sep 24, 2016
3,656
I am a very powerful guy because I have a lot of energy.

#### hevans1944

##### Hop - AC8NS
Jun 21, 2012
4,890
energy (as measured in watts) is the product of the volts and the amps.
Geez... I KNOW you know better than this completely wrong statement.

#### BobK

Jan 5, 2010
7,682
I am a very powerful guy because I have a lot of energy.
I have a lot of energy too.

Let's calculate it: 67Kg times c^2 = 67 x (3 x 10^8)^2 =

6.03 x 10^18 Joules.

Since a Joule is a Watt * Second, an 735 Watts is a horsepower. My energy is equivalent to:

8.2 x 10^15 HP * seconds.

Since there are 60 * 60 * 24 * 365 seconds in a year, that would be:

2.6 x 10^8 HP * years

So, theoretically I could produce 2.6 Million horsepower for 100 years.

But there is no way I could produce 1 HP for a minute. Go figure.

Bob

Last edited:

Jul 7, 2015
3,642

#### BobK

Jan 5, 2010
7,682
Your horse must be lame .
Damn, I looked that up and got the wrong answer. Actually, it is 746.

Bob

#### Tha fios agaibh

Aug 11, 2014
2,253
Let's not get pedantic on this one.

Thinking of a watt as energy(consumed) is what was trying to be conveyed to help the op understand.
I get kellys_eye's usage of the word "energy" although not technically correct.

#### BobK

Jan 5, 2010
7,682
There is nothing pedantic about it at all. It was a clear mistake that I wanted to correct so less knowledgeable people would not be misled.

Bob

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
I agree, the difference between energy and power is significant and somewhat akin to the difference between A and Ah. We rightfully point out where people use the latter pair incorrectly, so doing the same for the former is just bring consistent.

At the time, I was going to comment to @kellys_eye something along the lines of "but only if they're used for the same amount of time".

As I went back, I reread @Tha fios agaibh's preceeding post where he commits the reciprocal sin of saying that power is consumed, when it is more accurate to say that energy is consumed at the same rate, or that the energy consumed by both devices in the same period of time is the same.

Reading with the full context, rather than reading @kellys_eye's post in isolation lead me to the conclusion that both posts had what could be described as cancelling errors, sort of ERROR and ANIT-ERROR.

Knowing what terrible energies (or is that powers?) that are released when a particle and it's antiparticle annihilate each other, I decided that it was best not to perturb the posts lest they explode.

It is clear that these two posts have interacted in my absence, and this interaction has produced a shower of additional posts. The particle analogy suggests that these resultant posts may be short-lived, and that the original posts will be destroyed.

At the same time the OP, like some neutral, non-interacting particle has departed the scene, probably wondering what happened.

#### BobK

Jan 5, 2010
7,682
Power and energy are one of my pet peeves. It seems that every time I read an article about a new power plant or solar farm, they state it's output is megawatts per year. People just can't get their head around the fact that Watts is not a unit of energy. If they can't understand that megawatts is something that is produced continuously, at least they could change it to megawatt years per year.

Bob

Aug 13, 2011
1,114
True pedantry would look something like this.
I am trying to understand the difference between these two. They are LED lights that come on a strip, about 3 feet long.

One of them has these specifications: 120 Volts, 25 Watts

The other one has these specifications: 12 Volts, 25 Watts

So, what is the difference between them?
108V.
Do they both use the same exact amount of power?
Yes.
Why is there such a HUGE difference in voltage?
They are intended to operate from hugely different sources.
Yes.

Last edited:

#### Tha fios agaibh

Aug 11, 2014
2,253
I agree, the difference between energy and power is significant....
I reread @Tha fios agaibh's preceeding post where he commits the reciprocal sin of saying that power is consumed.

Duly noted folks. Please forgive my transgressions.
I will try to be more careful with the terms. (But old habits die hard)

Terms like "power outlet" (receptacle) lend to the confusion. It's widely misinterpreted as meaning; an outlet that supplies power.
In fact, its an outlet or that supplies energy.

Perhaps we need to change the term to energy outlet?

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