# How would a light bulb's Lumens increase with a decrease in Watts?

Thread Starter

#### ptownbro

Joined Sep 28, 2013
17
I believe I understand that you cannot directly connect watts to lumens because although they could/may be related, they represent different quantities (I guess it's akin to comparing height and weight measurements for a person). However, given the same exact light bulb, typically the higher the power, the brighter the light bulb. Or, the higher the watts the higher the lumens.

What could cause a result in a higher lumens for the same light bulb with a lower wattage?

I found the formula "watts = lumens / (lumens / watt)", but this doesn't really tell me much as to how or why (if I convert formula to lumens), watts result in a higher lumens, or how you can get higher lumens with a lower watts.

#### studiot

Joined Nov 9, 2007
4,998
How can it be the same bulb with a lower wattage?

#### Alec_t

Joined Sep 17, 2013
12,070
how you can get higher lumens with a lower watts.
Who says you can?

Thread Starter

#### ptownbro

Joined Sep 28, 2013
17
Me I guess. Haha. I'm still going for that nobel prize.

I'm talking about the source of the watts not the watt rating of the light bulb itself. In other words, if a power source put out some X lower Amps and resulted in Y increase in Lumens... assuming it's possible (just go with it)... how / what would cause that to happen?

As you probably guessed, my background is not in physics or electrical engeering (I can hear you all saying "duh" ), but I understand math and numbers. So I then to look at these things in the form of equations. Which is why when I look at the formula: w = lm/(lm/w)) I see both (1) something is missing and (2) that lower watts could result in higher amps (theoretically even though not likely).

#### ScottWang

Joined Aug 23, 2012
7,024
As the Technologies Today and Tomorrow, you can using a low watts and high Lumens LED to reached the same brightness with the high watts and high Lumens bulb, same or similar brightness but low watts, so how come the Watts and Lumens have any related today?

#### crutschow

Joined Mar 14, 2008
27,212
You can get more lumens with fewer watts with a different bulb that has higher efficiency (lm/watt) but the same bulb will always have lower lumen output with lower input power.

#### WBahn

Joined Mar 31, 2012
26,398
Me I guess. Haha. I'm still going for that nobel prize.

I'm talking about the source of the watts not the watt rating of the light bulb itself. In other words, if a power source put out some X lower Amps and resulted in Y increase in Lumens... assuming it's possible (just go with it)... how / what would cause that to happen?

As you probably guessed, my background is not in physics or electrical engeering (I can hear you all saying "duh" ), but I understand math and numbers. So I then to look at these things in the form of equations. Which is why when I look at the formula: w = lm/(lm/w)) I see both (1) something is missing and (2) that lower watts could result in higher amps (theoretically even though not likely).
Really? You are asking use to "go with it" and accept that something is possible even if it isn't and then we are supposed to explain how it is possible, even if it isn't? Really?

If you want to look at these things in the form of equations, then you need to learn to understand equations better. Give a specific example of how you think this relationship is claiming that it is possible to get lower watts with higher amps (where is amps even addressed in that relationship between watts and lumens).

Lumens/W is a constant that describes a particular bulb around a particular operating point. It tells you how many lumens of light you get out for every watt of electrical power you put in (under certain specified conditions).

For instance, I have a 40W bulb that outputs 400 lumens. That's 10 lumens/W. So if I upped the voltage and put in 45W I would expect about 450 lumens but if I lowered the voltage and put in 35W I would expect about 350 lumens. I doubt this relationship is linear over any significant range, but I do expect it to be monotonic.

#### studiot

Joined Nov 9, 2007
4,998
Pity you didn't answer my question.

It cannot be done with the 'same' bulb.

But bulbs of the same wattage come in several grades.
Standard grade.
Halogen quenched bulbs of the same wattage will yield a larger lumen output
So called 'Rough Service' bulbs will yield a lower lumen output
And mining and other confined spaces / hazardous atmousphere bulbs will yield even lower lumen output.

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#### KJ6EAD

Joined Apr 30, 2011
1,578
Don't be a dim bulb. See the table under "Lighting Efficiency" for typical values per technology.

http://en.m.wikipedia.org/wiki/Luminous_efficacy

• WBahn

#### WBahn

Joined Mar 31, 2012
26,398

#### kubeek

Joined Sep 20, 2005
5,753
w = lm/(lm/w)) I see both (1) something is missing and (2) that lower watts could result in higher amps (theoretically even though not likely).
First of all, there are no amps in that equation.
Second, that equations says that the power required will be the lumen output divided by the lumen per watt constant of the light source.

#### GopherT

Joined Nov 23, 2012
8,012
What could cause a result in a higher lumens for the same light bulb with a lower wattage?
By 'same light bulb', I assume that you mean two bulbs with equivalent wattage ratings - and you are asking about different lumen ratings.

There are various tricks. Several filaments in a parallel-series arrangement. Spiral wound filament has more surface area. Thin filaments operate at higher temp but shorter life (or lower temp, dimmer "severe duty" bulbs). Halogen gas (bromine usually) allows a higher operating temperature and brighter bulb per watt (see halogen cycle).

Thread Starter

#### ptownbro

Joined Sep 28, 2013
17
Yes, I understand that different bulbs of different technologies can produce same Lumens at lower watts. I'm talking about doing it with the same bulb.

For the same Bulb (without manually changing its composition) and given a lower Watts, what variable(s) would have to be changed to give you the same Lumens?

The standard equation given that I quoted doesn't say much about the relationship between watts and lumens and ignores any other relevant variables that could change to give the same or higher brightness at a give watt (it's effectively saying 1 = 1)

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And a special response Wbahn... Lightning up Francis. I said that to keep the conversation light. Geesh. Since we're going to there... Let me straighten you out. What I'm describing IS theoretical possible. So your statement is wrong. It may be unlikely, but it is possible. If you're going to argue that it's not possible, please also explain to me in all your brilliance why the Wright Bros. will never get a plane in the air. Now can we can back to being cordial?

#### studiot

Joined Nov 9, 2007
4,998
For the same Bulb (without manually changing its composition)
What you mean by the same bulb may be clear to you but is still not clear to me.

If you mean that you only have one bulb. Period.
Then how do you propose to supply it at lower wattage?

#### KJ6EAD

Joined Apr 30, 2011
1,578 What you're demanding is a license to break the laws of physics. You claim that it's theoretically possible to get more than marginal increases in lighting efficacy without a fundamental change in the underlying technology applied. Since it's your proposal, the burden of proof is on you.

Good luck with that.

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#### crutschow

Joined Mar 14, 2008
27,212
You are confusing what's theoretically possible with what's practically possible with real devices. We generally only deal with the latter in this forum. You seem to be hung up on what an equations might mean, not what they actually mean. Arbitrarily changing a parameter in an equation doesn't mean it describes a possible real outcome. • GopherT

#### GopherT

Joined Nov 23, 2012
8,012
For the same Bulb (without manually changing its composition) and given a lower Watts, what variable(s) would have to be changed to give you the same Lumens?
Oh, now I understand what you are asking. Sorry I confused the situation above. You need a RotoWatt. Connect your bulb in series with the power supply and dial in the wattage you want if you want to make your bulb efficiency higher. Connect it in parallel if you want Lower efficiency. You can add a dpdt switch or relay to make a full range of efficiencies.

#### WBahn

Joined Mar 31, 2012
26,398
What you have been asking is analogous to the following:

The standard equation for the distance that an object traveling in a straight line at a constant velocity V in time T is D = VT. So how can I increase V and get a smaller D in the same amount of time. Assume it's possible, how can it be done?

Now, having said that, there actually is an answer to your question. Namely, in order to get more lumens out of a bulb when you lower the wattage being delivered to the bulb, the bulb has to be operating at a point where the luminous efficiency increases as the power delivered is lowered. This is possible, since lumens is a measure of light as it is perceived by the human eye. As power is increased, the temperature of the bulb increases (assume we are talking about an incandescent bulb for discussion's sake) and the spectrum of the light emitted shifts moving from longer to shorter wavelengths. If you have a bulb that is operating at a high enough power that the bulk of the light emitted is at wavelengths shorter than the human eye can perceive, then it will have a very low luminous efficiency even though it is putting out a very large amount of light overall. As you lower the power, the total amount of light will drop, but the temperature might drop enough so that the fraction of it that is within the range of human perception might increase enough so that the total amount of light as perceived by the human eye actually increases. The only problem with this is that you would need to have a filament that is solid at temperatures in excess of that found at the surface of the sun.

• KJ6EAD
Thread Starter

#### ptownbro

Joined Sep 28, 2013
17
Studiot: Hm. I think I see the direction you're going. But let me ask with a simplistic example: Let's say we have a basic battery based circuit with a small 10 watt bulb and 2 batteries: one that is able to produce (or be drawn from) 30W and another at 20W. First you use the 30W battery in the circuit and you get a X lumens. Then, using the same 10W bulb, you switch to the 20W battery but this time you get an increase to Y lumens (I changed my example a bit).

Now my question: How would be able to produce a higher (or the same) Lumens with a lower Watts source like that in the same bulb?

And to those of you want to frantically inform me "that's not possible!", "that's breaking the laws of physics!", "good luck with that", "we only discuss what's practical here"... blah, blah, blah.. I get it. But, can I just ask the question please? GopheT: Thank you! That was very helpful in helping me conceptualize what I'm trying to do. However, I'm looking for the actual variable (like heat, or?) that could cause the change in lumens. And, I tend to focus on the equations because the math helps me (at least) understand better and call out the variables causing the changes.

Thread Starter

#### ptownbro

Joined Sep 28, 2013
17
What you have been asking is analogous to the following:

The standard equation for the distance that an object traveling in a straight line at a constant velocity V in time T is D = VT. So how can I increase V and get a smaller D in the same amount of time. Assume it's possible, how can it be done?

Now, having said that, there actually is an answer to your question. Namely, in order to get more lumens out of a bulb when you lower the wattage being delivered to the bulb, the bulb has to be operating at a point where the luminous efficiency increases as the power delivered is lowered. This is possible, since lumens is a measure of light as it is perceived by the human eye. As power is increased, the temperature of the bulb increases (assume we are talking about an incandescent bulb for discussion's sake) and the spectrum of the light emitted shifts moving from longer to shorter wavelengths. If you have a bulb that is operating at a high enough power that the bulk of the light emitted is at wavelengths shorter than the human eye can perceive, then it will have a very low luminous efficiency even though it is putting out a very large amount of light overall. As you lower the power, the total amount of light will drop, but the temperature might drop enough so that the fraction of it that is within the range of human perception might increase enough so that the total amount of light as perceived by the human eye actually increases. The only problem with this is that you would need to have a filament that is solid at temperatures in excess of that found at the surface of the sun.
Thank you! I'm going to have to re-read and let this soak in a bit more, but so far I think I've understood you correctly. Thanks again!

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