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Luminance Versus Luminosity


Kevin Stecyk
 

Hello Folks,

Can someone, please, tell me the difference between “luminance” and “luminosity” in layman terms?

This August, I took a CELTA course, which allows graduates to teach English to foreigners. I thought if I take a long trip somewhere, I could teach English for a while to help pass time.

At present, I am providing pro bono English lessons to a Chinese woman. As part of my teaching, I assign articles about various topics every week. I highlight words that I want her to define, and I usually assign an essay based upon or related to the article. An upcoming study article from 2011 discusses cosmetics and mentions the words “luminance” and “luminosity.”

I went to Merriam-Webster Dictionary and wrote the following definitions:

1.       Luminance: noun, the quality or state of being luminous. That means that luminance refers to how shiny, bright, or reflective the object is.

2.       Luminosity: noun, the quality or state of being luminous. In other words, it is a measure of the object’s brightness.

I might have misinterpreted the dictionary’s definitions. These two words look very similar to me. Perhaps for the average person, these two words are synonymous?

·         The participants judged women made up in varying intensities of luminance contrast (fancy words for how much eyes and lips stand out compared with skin) as more competent than barefaced women, whether they had a quick glance or a longer inspection.

·         “There are times when you want to give a powerful ‘I’m in charge here’ kind of impression, and women shouldn’t be afraid to do that,” by, say, using a deeper lip color that could look shiny, increasing luminosity, said Sarah Vickery, another author of the study and a Procter & Gamble scientist. “Other times you want to give off a more balanced, more collaborative appeal.”

Although I have provided the specific sentences, please don’t anchor your answer solely on those sentences. Instead, I like the student to understand how these two words should be used and applied in a general context. And because she is not a color theory professional, pedantic answers are not required—general answers are sufficient.

How would you define these two words to a woman who is learning English with regard to cosmetics?

Thank you for your help.

Sincerely,

Kevin


Daniele Di Stanio
 

Hi Kevin,

I spent a great deal of time reading about color terminology lately. This answer is coming from Hunt's "The reproduction of colour", sixth edition, Chapter 7.

The author explains that:

"In colour, both the response of the observer (the subject) and the physical nature of the stimulus (the object) are important, and it is necessary to distinguish clearly between these subjective and objective aspects of colour. The terms hue, colourfulness, brightness, lightness, chroma and saturation [...] are clearly all subjective terms. Objective terms denote quantities obtained with measuring instruments [...]"

This to me is the best and easiest example to use and comprehend both words. Two notes.

First, the author explains that "luminosity" was used in place of brightness in the past.

Second, different fields can significantly switch the meaning of terms, color correction has a meaning for us, but in the cosmetics industry is about hair color change ("hair color correction" has more than 50 millions results on Google).

Hope this helps! 

Daniele Di Stanio



On Sat, Nov 2, 2019 at 12:32 PM Kevin Stecyk <stecyk@...> wrote:

Hello Folks,

Can someone, please, tell me the difference between “luminance” and “luminosity” in layman terms?

This August, I took a CELTA course, which allows graduates to teach English to foreigners. I thought if I take a long trip somewhere, I could teach English for a while to help pass time.

At present, I am providing pro bono English lessons to a Chinese woman. As part of my teaching, I assign articles about various topics every week. I highlight words that I want her to define, and I usually assign an essay based upon or related to the article. An upcoming study article from 2011 discusses cosmetics and mentions the words “luminance” and “luminosity.”

I went to Merriam-Webster Dictionary and wrote the following definitions:

1.       Luminance: noun, the quality or state of being luminous. That means that luminance refers to how shiny, bright, or reflective the object is.

2.       Luminosity: noun, the quality or state of being luminous. In other words, it is a measure of the object’s brightness.

I might have misinterpreted the dictionary’s definitions. These two words look very similar to me. Perhaps for the average person, these two words are synonymous?

·         The participants judged women made up in varying intensities of luminance contrast (fancy words for how much eyes and lips stand out compared with skin) as more competent than barefaced women, whether they had a quick glance or a longer inspection.

·         “There are times when you want to give a powerful ‘I’m in charge here’ kind of impression, and women shouldn’t be afraid to do that,” by, say, using a deeper lip color that could look shiny, increasing luminosity, said Sarah Vickery, another author of the study and a Procter & Gamble scientist. “Other times you want to give off a more balanced, more collaborative appeal.”

Although I have provided the specific sentences, please don’t anchor your answer solely on those sentences. Instead, I like the student to understand how these two words should be used and applied in a general context. And because she is not a color theory professional, pedantic answers are not required—general answers are sufficient.

How would you define these two words to a woman who is learning English with regard to cosmetics?

Thank you for your help.

Sincerely,

Kevin


Michael Colby
 

Unless she’s a photographer or an artist she’s not going to care that in that context luminance is brightness of light, eg the L channel of LAB, or brightness of an area of an image on a screen measured in cd/m2 (squared). 


and luminosity is the combination of luminance and edge contrast that yields the perception of depth and structure in a 2D image. 


onelistdrs
 

Suggest you search for "luminance vs luminosity"
using Duck Duck Go or Google or your fav search engine.

Doug


Kevin Stecyk
 

Hi Folks,

I am going to respond to the three people who have volunteered answers so far. I am deeply appreciative of their help.

Doug

Thank you for suggesting that I use a search engine to begin my quest of understanding the difference between luminosity and luminance. Before I posted my question, I had a brief look on the internet to see if there was an easy answer. By brief, I took less than five minutes.

One of the things I have learned is that the information on the internet isn’t always reliable. For help with teaching English, I have found that some of the information on the internet is plain wrong. With other technical items, the information might be wrong or overly technical and complex.

There are at least a couple of advantages of asking a question in a forum. One is that I can frame my question. As I discussed in my original post, I am not looking for a highly technical answer. I just want to be able to describe the differences to a person learning English so that if she comes across these words in her daily life, she knows what is being communicated. And the other refers to a quote by Robert A. Heinlein: “When one teaches, two learn.” Not only do the people asking and responding to the question benefit, but sometimes others who are lurking learn something, too. So, it’s all good.

You provided three links. The first link I didn’t find helpful. I saw the second link prior to my original post. And the third link is interesting.

Under the title of “Luminosity,” the author states two things:

1. Technically, luminosity of a light source is a measure of the light energy emitted, typically measured in Joules per Second. Imagine light as a cylinder of energy coming from a torch. Turn the torch on for a second and capture that cylinder (which will of course be quite long, given the speed of light). Or maybe have some transducer that turns light into heat (a simple black box around the torch will do), then turn on the torch for a second and measure how much hotter the box now is (so not that much energy).

2. In computer image editing, luminosity is one component of Hue, Saturation and Luminosity or HSL, which is an alternative to Red, Green Blue (RGB) representation of pixels. The L in HSL can also stand for Lightness or Luminance, depending on the source of the editing software used, which shows the looseness by which these terms can be used.

And then under the title of “Luminance,” the author states two additional things:

1. Technically, luminance of light is a measure of the luminous intensity per unit area of light travelling in a given direction. You can take the same amount of light energy and have it concentrated at a point or spread over a wider area. The point seems brighter than the area because the intensity per unit area is higher, even though the total energy is the same. In other words, luminance is a measure of light not over time (like luminosity) but over an area.

2. In photo editing, luminance can appear as the L in HSL. It also appears in 'Luminance masking' where a layer mask is based on a limited range of dark or light within the image. This lets you edit these areas directly, for example making them more light or dark, or even changing their hue or saturation.

So, if I were to put these explanations into my own layman words, I would say that luminosity measures the flow of light. You might think of light as water, and luminosity as a river. The stronger the river, the brighter and more energetic the light. And luminance might be thought of as a lake. The deeper the lake, the brighter the light. In both cases, the casual observer notices brightness when either luminosity or luminance used.

For a person at a cosmetics counter, luminosity and luminance are likely interchangeable. Even the author mentioned that for photo editing software, luminance and luminosity are often used interchangeably. So, whether it’s hair color, nail polish, eye shadow, lipstick, or some other cosmetic item, luminosity and luminance simply means brightness to a consumer.

 

Daniele Di Stanio

Thank you for responding.

You answer seems to confirm my suspicion that “luminosity” and “luminance” can be used interchangeably to communicate brightness to consumers in the cosmetics industry.

As we know, consumers will have their own subjective preferences and standards for color. Their technical instruments are their eyes and a mirror. Armed with that technical information, consumers make their choices.

 

Michael Colby

Thank you for responding.

Am I correct in my earlier comments about luminance being light over an area (depth of a lake) and luminosity being the energy or flow of light (flow of a river)?

In your response, you mentioned that “. . . luminosity is the combination of luminance and edge contrast that yields the perception of depth and structure in a 2D image.”

Although this next question or request is beyond helping my student, your response piqued my curiosity. Could you, please, expand how luminosity is the combination of luminance and edge contrast that yield perception of depth and structure in a 2D image?

If the explanation is long and complex, then, perhaps, your effort is not warranted because of my simple curiosity. But if you can provide a further explanation in a couple or few paragraphs, I would like to know more.

 

Again, I am thankful to everyone who has responded.

 

Kevin


Michael Colby
 

I derive my explanation from experience and from multiple sources, especially this write up from Photographer and master B&W printer, George DeWolfe.  He Discussed this, too, in his book B&W Printing


Kevin Stecyk
 

Thank you, Michael.

I enjoyed reading your enclosed PDF. It seems as though he is defining  luminance as seeing and  luminosity as perception. The true reality as measured by a machine is luminance whereas luminosity is our reality through our perception.

It's interesting how different people define words differently. I gather George DeWolfe's definitions are more artistic in nature. That is, a physicist might define those two words differently.

For my student, I think I am going to simplify everything by saying that both words in everyday language essentially mean the same thing: brightness. Most  nonexperts and non-artists probably define both words in a similar fashion.