# Talk:Luminosity

## Untitled

How does one get from those parameters to the simplification? Can someone check the work? lysdexia 22:40, 18 Oct 2004 (UTC)

## Merge articles

If luminance and luminosity are supposed to be synonyms, shouldn't those two articles be merged? --Abdull 12:01, 23 Mar 2005 (UTC)

Just because "luminance" is sometimes called "luminosity", that doesn't mean that "luminosity" can always be called "luminance". There are at least two different quantities involved here.
Maybe it needs to be explained more clearly in both of these articles, as well as in the Template:SI light units which appears on both pages, and which can be edited by going there. Can you or someone else look into that? There might be differences in usage between physics and electronics and astronomy, for example, as well as differences in recommended usage over time. What are the official current recommendations of any of the multitude of standards organizations which might be involved in this? Gene Nygaard 13:15, 23 Mar 2005 (UTC)
There are at least five different meanings of the two words between the two pages (although some are not spelled out clearly). The two words are only synonymous for some of those meanings, so merging the pages is out of the question. BTW. I have renamed the "SI light units" chart. The units described are specifically for photometry. They do not encompass all of the meanings of luminance and luminosity.--Srleffler 06:53, 12 November 2005 (UTC)
Luminosity in particle physics/scattering is certainly different from luminance. If the astronomical parts of the articles are merged, the particle physics part should certainly be kept under "luminosity". HEL 22:46, 30 September 2006 (UTC)
You're replying to a very old comment. There is no current proposal to merge anything here.--Srleffler 05:51, 1 October 2006 (UTC)

## Classification of stars according to luminosity

Hi I wanted an article on the subject I have mentioned but I could not find it. Could you please find an article on the above—The preceding unsigned comment was added by 202.142.94.106 (talkcontribs) 05:49, May 19, 2006.

Try Category:Stars by luminosity class.--Srleffler 05:54, 1 October 2006 (UTC)

## Usage in HSL

Glennchan says: "please cite sources- the additional information is contradictory; read the luminosity and HSL wikipedia pages." OK, I'll try for some sources. But I don't see what the contradiction is that you see. Can you clarify? Dicklyon 01:32, 20 November 2006 (UTC)

Never mind. I think I see the point that lightness is not the same as luma, even if Photoshop's terminology did influence both. Dicklyon 01:41, 20 November 2006 (UTC)

## Definition of lightness in color science in case you are interested

Glennchan 08:16, 20 November 2006 (UTC)

## What does the L in HSL color space stand for?

Why don't we move this information into the HSL color space page, not this one. I think the only relevant info here would be that the "L" in HSL color space is called different things.

As far as the correct name / what L stands for... I do not know. Since in common usage various L words are used, it is useful to point that out. If there is some authority for naming conventions, then please add that information and cite that authority (i.e. like how SI handles standard units and nomenclature for science/physics).

In a slightly different vein, you can point out that the "L" in HSL has nothing to do with the color science definitions of luminance, lightness, etc. There's no connection with color science there. Glennchan 04:27, 22 November 2006 (UTC)

Well, all I can cite for now is that books calling it hue-saturation-lightness are much more common, at least before 2000, than those calling it hue-saturation-and-luminance. The idiosynchratic max-min thing is clearly unrelated to anything from color science. We can defer the confusion to the HSL page if you prefer. Dicklyon 06:02, 22 November 2006 (UTC)

## Apparent, visible, total, bolometric, luminosity and magnitude

I tried to clarify this more, but please check and see if I got it right. The proliferation of terms here is confusing and could maybe use more work. Dicklyon 19:36, 27 February 2007 (UTC)

## Brightness-Luminosity examples

This is not a textbook. I don't think sample physics problems should be included in this article. What do you all think? Stebbins 06:09, 15 May 2007 (UTC)

• I am for them. I think they're helpful to make sure readers understand the point the article is trying to get across. --pie4all88 12:40, 26 October 2007 (UTC)
• I added the Sirius example originally with the formula. I think it's complicated enough than an explicit example helps explain how to use it. Tom Ruen 18:09, 26 October 2007 (UTC)
• Examples are very helpful. I will be providing blue links to the Betelgeuse article since the variability of this supergiant presents some interesting challenges when computing luminosity.--Sadalsuud (talk) 02:40, 28 June 2012 (UTC)

The Main sequence and the Luminosity articles give contradictory information about luminosity being proportional to a power of stelar mass. The Main Sequence article mentions M^3.5 while the luminosity article mentions M^3.9. Could someone correct this? -Paul- (talk) 01:27, 9 February 2008 (UTC)

I've seen the M^3.5 figure elsewhere, though it doesn't seem to be in the main sequence article any more. It may be outdated, but if so, it would be good to have the source for M^3.9.JW Bjerk (talk) 17:02, 18 October 2009 (UTC)

## Units

The units in the luminosity formula for stars are not specified, but appear to be in light years. However, the standard astronomical formulae use parsecs as the unit. For example, the absolute magnitude of a star is given as the brightness of a star at a distance of 10 parsecs (32.6158 light years). The constant -2.72 also needs some explanation; it appears to be the brightness of the sun at a distance of 1 light year but this is not explained. The article could be improved by adding units and supplying a clarifying explanation for this constant. -- B.D.Mills  (T, C) 00:04, 25 February 2008 (UTC)

On top of that I don't get results that add up with the formulas in this article that I have tested with Extra Solar planet star data. Specifically:
${\displaystyle {\frac {L}{L_{\odot }}}={\left({\frac {R}{R_{\odot }}}\right)}^{2}{\left({\frac {T}{T_{\odot }}}\right)}^{4}}$. and

Lstar/${\displaystyle L_{\odot }}$ = (diststar/distsun)2 · 10[(msun −mstar) · 0.4]
Lstar = 0.0813 · diststar2 · 10(−0.4 · mstar) · ${\displaystyle L_{\odot }}$

I'll have to dig up the examples from the extra solar planet catalog...
GabrielVelasquez (talk) 04:54, 25 June 2008 (UTC)

I found that using radius in kilometers worked, if anyone can confirm this perhaps these units should be stated. Firstmatekevin (talk) 15:08, 8 July 2010 (UTC) kevin.

## Luminosity vs. Luminous flux

Could someone please add a paragraph explaining the difference between luminosity and luminous flux -and why luminosity is not measured in lumens? Perhaps a link from the luminous flux page too? 71.129.86.9 (talk) 01:04, 20 March 2010 (UTC)

## Luminosity definition (first paragraph in astronomy sec.)

Luminosity is the amount of light radiated per second. Multiple sources can be used to verify this / support this change. What does everyone think? (Rest learned/ read about it in my astronomy class.

(NB: It's helpfull, if you sign you text with four tildes) What you say, is actually just what the text states now: "Electromagnetic energy a radiated per unit of time" is just a bit more precise words for the same thing.
However your words might be easier to understand for many readers. One could argue, that i.e. radio and x-ray emmissions should be included, and they are more clearly included in "electromagnetic radiation" than in "light". However that might be a detail, compared to making the opening paragragh overly technical. I'd say go ahead and change it.
By the way, I guess we should add a mention of the unit is for Luminosity being watts. Esp. since the units for spectral luminosity is mentioned right after. Tøpholm (talk) 23:56, 11 March 2011 (UTC)

## Brightness is perceived

The section on uses in astronomy, at times used the word brightness as the thing that is measured, which is wrong. The magnitude is measured, brightness is a perception of this (i.e. if you are drunk, brightness will be affected, the magnitude however is an objective measure).

So the heading "Computing between brightness and luminosity" should be changed to "Computing between magnitude and luminosity".... however this exact wording is used for the title of a subsection, which is actually only about differences in absolute magnitudes. So I guess both titles should be changed? Tøpholm (talk) 23:44, 11 March 2011 (UTC)

## Luminosity != Luminance

I think that the article begins wrongly by saying that Luminosity is another term for brightness. Luminosity is the term for total amount of light, i.e. in Watts (or perhaps the photometric equivalent).

So should the article be restructured to give first the simple definition "Luminosity is a measure of the total amount of light emitted (in all directions) by a source"; then the Astrophysics examples, and then finally the "common misuse" instances as synonyms for "luminance" and "luma" ?

At the moment, the article begins with a wrong sentence (comparing luminosity to brightness), and then spends the opening 2 sections explaining what luminosity isn't! — Preceding unsigned comment added by 87.194.171.29 (talk) 21:13, 27 February 2012 (UTC)

Let's get some sources first. I usually object to saying "X is incorrectly used as ..." unless there's a source that says so. But in this case I see it was I who inserted the first "incorrectly", as an inexperienced wikipedian back in 2006. Before we reorganize around one use of the term, I'd like to see what sources have to say about that and other usages. The "incorrect" uses may still be documented legitimate uses and maybe should be presented as such. Dicklyon (talk) 21:24, 27 February 2012 (UTC)

## Polishing the article

I've been working on a variety of astronomy articles, Betelgeuse most recently, and noticed the two tags at the top of the article, one for added citations and the other for an expanded lead section. The formulas provided in this article figure prominently in the Betelgeuse article. So I'd like to contribute to this article if I can, especially since it's High Importance. The only contribution I can make, however, is that of a layman struggling to understand what for me is often a challenging subject.

I looked at all the other articles that might reference back to this article, Photometry, Luminance, Luma (video), HSL color space, Scattering theory and accelerator physics, but noticed that none of them use blue links to link back to this article. Consequently, the majority of readers who come to this article, I suspect, come via some star article, specifically the Details section of the starbox. For this reason, I think it makes sense to have the Astronomy section come first in the article, with other sections to follow

The sub-section on astronomy is very helpful in that it provides sophisticated formulas to convert from one luminosity distinction to another. Where the article is weak is that it's a little esoteric for the average reader. I will therefore be working on the article a little to make it more "user-friendly", expanding the lead and adding citations, but feel free to edit at will. I will be posting ideas for article improvement as sub-sections below: Thanks.--Sadalsuud (talk) 14:27, 27 June 2012 (UTC)

### Structure

In terms of structure, I think it's best to have the Astronomy section come first, for reasons mentioned above. Also article headings all start with "In", which strikes me as somewhat redundant. I think shorter phrases work better, especially if there exist articles written on the subject.--Sadalsuud (talk) 15:05, 27 June 2012 (UTC)

### New sections

It appears we might be missing 2 sections:

1. When clicking on the Wiktionary link, I notice a physics definition, which provides many "luminous" distinctions: 1) luminous flux, radiant flux, luminosity factor. Do we need a separate section here?
2. The other section that might be missing is Astronomical Photometry

### Removed tags

• OK. I removed the "Expanded lead section" tag. I think the lead is decent. Any thoughts on how to improve it would be great.--Sadalsuud (talk) 10:44, 30 June 2012 (UTC)
• I removed the "Need citations" tag from 2006. We're on our way. There are still more to add, but the number is sufficient to justify removal.

## Energy or power?

I'm no expert, but luminosity appears to measure energy per unit time. So wouldn't it be more appropriate to have the lede state that the luminosity is the amount of power emitted by the body, rather than energy? William Jockusch (talk) 01:21, 11 October 2012 (UTC)

## Disambiguation

This article seems to be about four or five completely different things. Isn't the standard practice to have four or five different articles with a disambiguation page? Lithopsian (talk) 20:26, 17 November 2012 (UTC)

I agree, Should have 2 articles (not five imo). One about luminosity in astronomy and one for color theory. The sections on Optical photometry and Computer graphics should be part of that color theory page. But I don't know how to make a luminosity(color theory) page or a disambiguation page...217.122.183.107 (talk) 16:55, 11 April 2013 (UTC)
Luminosity in scattering theory now has its own article written in Jan 2013: Luminosity (scattering theory). The other non-astronomy sections just point to articles in those areas. I will make a disambiguation page, Luminosity (disambiguation), along the lines of Luminance (disambiguation) for those sections. StarryGrandma (talk) 14:44, 25 April 2014 (UTC)

## Possibly wrong number for Sun's power output?

This article says: "The Sun has a total power output of 3.846×10^26 W or 1.00 solar luminosity,"

http://en.wikipedia.org/wiki/Solar_luminosity says: "One solar luminosity is equal to the current accepted luminosity of the Sun, which is 3.839×10^26 W," ... "3.939×10^26 W if the solar neutrino radiation is included as well as electromagnetic radiation"

https://www.cfa.harvard.edu/~dfabricant/huchra/ay145/units.html says: "1 Solar Luminosity = 3.826x10^26 W"

http://nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html says: "Luminosity = 3.846x10^26 W" and hence agrees with the article. But what about http://en.wikipedia.org/wiki/Solar_luminosity then? God, maker of the world (talk) 06:03, 12 April 2014 (UTC)

Wrong isn't the right term. Some of the articles may not be quoting the latest measurements. Measuring energy output across the entire spectrum is tricky, and these measurements are close to each other. The NASA Sun Fact Sheet (kept up to date) gives 3.846 x 1026. I'll put the reference in. StarryGrandma (talk) 19:38, 13 April 2014 (UTC)

## Luminosity and brightness

I am putting brightness back into the lead paragraph. It is helpful for non-technical readers to understand the relationship between them. There is a Wikipedia article brightness, but it is about perception, not the astronomical usage of the word. Brightness has a different meaning in astronomy.

As a reference for brightness and luminosity I am using

• Hopkins, Jeanne; Foreword by S. Chandrasekar (1980). Glossary of Astronomy and Astrophysics (2nd ed.). The University of Chicago Press. ISBN 0-226-35171-8..

Jeanne Hopkins edited manuscripts for the Astrophysical Journal and compiled this glossary for authors to make her job easier. In disputes between authors about definitions, the astrophysicist Subrahmanyan Chandrasekhar served as referee. At the time he was the Managing Editor of the journal, and he proofread this second edition when it was published. He won the Nobel Prize for Physics in 1983.

brightness: Measure of the luminosity of a body in a given spectral region. (page 21)
luminosity: Total radiant energy output per second; the amount of energy radiated at the surface of a star: L = 4πR2σT4 See also Stephan's Law. (page 104)
magnitude: An arbitrary number, measured on a logarithmic scale, used to indicate the brightness of an obect. If li is the brightness of star i, and mi is its magnitude, then m2 - m1 = 2.5 log (l2/l1). Two stars differing by 5 mag differ in luminosity by a factor of 100. 1 magnitude is the fifth root of 100, or about 2.512. The brighter the star, the lower the numerical value of the magnitude (see also Pogson's ratio). (page 107)

StarryGrandma (talk) 20:56, 2 May 2014 (UTC)

## SI Units?

This page opens up by saying that "In SI units luminosity is measured in joules per second or watts". While it is most often measured in these units, the technical SI unit for luminosity is the candela. Additionally, luminosity and therefore candelas are some of the few SI units that are not derivations of other units; the Joule itself is defined as kg·m2·s-2. Just a little concerned about article consistency.

Jacob S-589 (talk) 21:09, 15 November 2014 (UTC)

I don't think so. Candela is the SI unit for luminous intensity, not luminosity; the latter is defined in terms of power and energy, not visibility to human eyes like the former. Dicklyon (talk) 23:35, 15 November 2014 (UTC)

## Neutrinos do not drive winds in normal stars

The article claimed: "A star also radiates neutrinos, which carry off some energy, about 2% in the case of our Sun, producing a stellar wind and contributing to the star's total luminosity.[5]". Citation 5 says nothing at all about stellar winds, and in fact only in supernovae are there thought to be enough neutrinos to drive a wind. Removed the mention of wind; the intent might have been to include kinetic energy of the wind in the Sun's output, but that needs more discussion. — Preceding unsigned comment added by 192.87.1.200 (talk) 13:16, 19 January 2015 (UTC)

## Another archived source

Most stars don't have a measured radius or a trigonometric distance, so their luminosity is determined by other means. One step involves spectroscopic parallax. See https://web.archive.org/web/20140809120004/http://www.atnf.csiro.au/outreach//education/senior/astrophysics/photometry_specparallax.html, archived 9 August 2014. StarryGrandma (talk) 18:57, 13 February 2015 (UTC)

## Removing Computational challenges section

I am removing this section, long labeled as citation needed. I can't find references that discuss this. This is a special case, since we don't have diameters for most stars and find luminosity by other means. StarryGrandma (talk) 20:22, 7 October 2016 (UTC)

The section has a heading comment stating "----------This section has been referenced by the Betelgeuse article---------", but I don't see anything in the Betelguese article to support it. StarryGrandma (talk) 20:27, 7 October 2016 (UTC)
Ah, that meant that the Betelguese article had a reference note that referred to this section. I've removed the note. StarryGrandma (talk) 20:54, 7 October 2016 (UTC)
The given calculations were probably best removed in any case. They failed to mention important concepts such as effective temperature, not just any old temperature. While we do have angular diameters, and hence linear diameters, for a good many stars, it is certainly not a typical way to find a stellar luminosity. It is more likely to be used to backtrack and cross-check other calculations. The tight relationship between radius, effective temperature (or occasionally a different temperature with a suitable reference radius), and bolometric luminosity is often seen. It is directly inferred from the Stefan–Boltzmann law. Lithopsian (talk) 21:12, 7 October 2016 (UTC)

## ${\displaystyle L_{\odot }}$ visual or bolometric?

Under "Magnitude formulae" I see two statements which seem to differ:

• ${\displaystyle L_{\odot }}$ is the solar visible luminosity
• ${\displaystyle L_{\odot }}$ is the Sun's (sol) luminosity (bolometric luminosity)

Is the symbol ambivalent? Kipala (talk) 09:42, 5 December 2017 (UTC)

What an awful section. Equating (distinguishing?) apparent and bolometric magnitudes is like trying to describe the different between green bananas and straight bananas and then thinking you've described all bananas. I'll see if I can fix it, but might end up chopping the whole lot and referring to existing articles on astronomical magnitudes. Back to your original question, L (there's a template {{solar luminosity}}, very handy), and even the word luminosity in general, very rarely refers to only the flux in a particular wavelength band. Most modern astronomers would be baffled by that usage, just because it is something they'd never think to do. I can't find a strongly-worded official prohibition on it, but plenty of definitions for L that refer only to bolometric luminosity. I'd recommend avoiding any use of "visual luminosity" like the plague; stick to visual magnitudes, there really isn't any need or use for converting them into energy or luminosity units. Lithopsian (talk) 17:27, 5 December 2017 (UTC)

## Picture???

Does anybody know of a good picture for the intro to this article? Sam-2727 (talk) 01:19, 24 March 2019 (UTC)

Maybe a H-R diagram like this one? Dicklyon (talk) 03:33, 24 March 2019 (UTC)

there is already an HR diagram in the article though Sam-2727 (talk) 21:25, 24 March 2019 (UTC)

Maybe a picture of the sun, to illustrate what L is? Headbomb {t · c · p · b} 21:34, 24 March 2019 (UTC)

ok I added that Sam-2727 (talk) 16:42, 25 March 2019 (UTC)

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