Talk:Photometry (optics)

P. S. Joke. Funny. Ha ha. Do not insert this material into any article.

--->  :-) <---

Note smiley. Dpbsmith 02:09, 20 Jun 2004 (UTC)

"Watts can also be a measure of output. In a radiometric sense, an incandescent light bulb is about 80% efficient; 20% of the energy is lost (e.g. by conduction through the lamp base) The remainder is emitted as radiation. Thus, a 60 watt light bulb emits a total radiant flux of about 45 watts."

How much of the total radiant flux is in the visible spectrum? What are the comparable numbers for current fluorescent bulbs? What are the comparable numbers for current LED-based bulbs?-69.87.204.232 11:46, 19 May 2007 (UTC)Reply

This article is missing the terms for reflectance/reflectivity. What are they?-69.87.204.232 11:46, 19 May 2007 (UTC)Reply

Photometry compensates for the spectral response of the human eye, but not the non-linear intensity response.

The apparent brightness of a point source diminishes with the square of the distance. But if the source is big enough to appear as an area, the apparent brightness is constant with distance, because the apparent size varies to compensate for the light received.

The most common unit to rate small bulb/lamps is mcd, millicandela.

These matters should be mentioned in the article.-69.87.203.79 18:24, 19 May 2007 (UTC)Reply

Q. Does a 200 mcd LED appear twice as bright to the eye as a 100 mcd LED?

A. No, but it will appear somewhat brighter. The eye can detect an increase or decrease in light only when its intensity is doubled.

[1] -69.87.203.48 19:57, 19 May 2007 (UTC)Reply

The above answer is nowhere near the truth. Around a few percent brighter is more like the detection threshold, though it depends on a lot of things. But nonlinear brightness perception is not a photometry-related topic. Maybe we need to be more clear in the lead that photometry measures weighted power linearly. Dicklyon 20:03, 19 May 2007 (UTC)Reply

Such issues are implicitly relevant in any physics subject which is trying to model (partially) the human response. If details don't belong here, they do belong somewhere, and to be mentioned/linked here. This is currently the master article for learning about lighting. Non-linear intensity response is a key lighting concept.-69.87.203.97 14:18, 20 May 2007 (UTC)Reply

This entire article is based on spectral weighting. But the actual curve and data values are not included; only a couple sample points are mentioned. Links were added. They were removed. So, here they are: numeric graphic 1988 C.I.E. Photopic Luminous Efficiency Function
(The functions should be annotated with color names to make the information as accessible as possible to the general reader.) -69.87.203.97 14:18, 20 May 2007 (UTC)Reply

"Candelas are equal to the square of the distance multiplied by the number of footcandles. For example, if your meter is ten feet away from the light source and your meter reading is 10 footcandles, the equivalent candelas equals 10 feet squared (e.g. 100) times 10 -- which equals 1,000 candelas.

The conversion of footcandles and lux to candelas is most accurately achieved in the context of a single point source of light measured in the dark. If the light source is diffused, you should take several readings at different angles in order to calculate an "average" candela measurement." [2]

"The name "footcandle" conveys "the illuminance cast on a surface by a one-candela source one foot away." As natural as this sounds, this style of name is now frowned upon, because the dimensional formula for the unit is not foot · candela, but lumen/sq ft. Some sources do however note that the "lux" can be thought of as a "metre-candle" (i.e. the illuminance cast on a surface by a one-candela source one meter away). A source that is farther away casts less illumination than one that is close, so one lux is less illuminance than one footcandle. Since illuminance follows the inverse-square law, and since one foot = 0.3048 m, one lux = 0.3048^2 footcandle ≈ 1/10.764 footcandle."

So, lux can be converted directly to candela, without computing footcandles. Just multiply the lux reading by the square of the distance, measured in metres. -69.87.203.133 01:37, 25 May 2007 (UTC)Reply

Much of this physics/geometry is based on idealized point sources. Almost all sources can be viewed as either area or point sources, depending on relative distance. Within the near-field, they tend to be area sources emitting an even field of flux, In the far-field they tend to be point sources with the flux spreading out according to inverse square law. And there is the mixed transition zone in-between, hardest to model. It seems like this whole concept should be mentioned somewhere in this article, and discussed in some detail somewhere.

When you look at a source of light that subtends a visible size, the brightness is constant with distance, because as you get farther and your eye receives less light, it also appears smaller, to exactly compensate. But when you get far enough away to see it as just a point, then it does appear to get dimmer as you get farther away. Maybe someone with a good understanding of these matters could pitch in and make sure they are covered in the appropriate places?

Does WP have some good articles somewhere covering how the human eye works? Seems like there should be links to such from this article. -69.87.203.133 01:50, 25 May 2007 (UTC)Reply

The article should have lots of formulas. Here is a good basic resource with such content: [3]. Someone reverted it out of the article, so it is up to you now.-69.87.203.9 12:05, 30 May 2007 (UTC)Reply

This page has a number of detailed radiometer detector spectral curves, from 200-2000 nm.[4] It would be great to have details about photo detectors of various types in WP.-69.87.203.9 12:05, 30 May 2007 (UTC)Reply

I'm interested in physics and wanted to better understand the meaning of the different photometric quantities. Therefore (as a software developer) I started to implement an applet that calculates and visualises the different photometric quantities in my spare time... Please have a look at it on http://www.energysavinglamps.info/photometry_applet.html I would be glad to contribute a link to it to Wikipedia.

Do you think it is worth an external link?

(The site is pure informational, not commercial, and will be extended soon) Otherwise I would appreciate any suggestion for improvements. Mtidei 11:52, 12 October 2007 (UTC)Reply

I understand your desire to contribute. Wikipedia is fairly conservative about external links, and for good reason since there is an unending supply of people who want to use Wikipedia to drive traffic to their sites. The policy on external links is at Wikipedia:External links. In particular, under "Advertising and conflicts of interest" it says:

Due to the rising profile of Wikipedia and the amount of extra traffic it can bring a site, there is a great temptation to use Wikipedia to advertise or promote sites. This includes both commercial and non-commercial sites. You should avoid linking to a website that you own, maintain or represent, even if the guidelines otherwise imply that it should be linked. If the link is to a relevant and informative site that should otherwise be included, please consider mentioning it on the talk page and let neutral and independent Wikipedia editors decide whether to add it. [Emphasis mine]

The idea here is that to avoid conflict of interest you should not be putting links to your own work on Wikipedia. Your applet is online and you've mentioned it on this talk page. If it is good enough, someone else will add a link to it.--Srleffler 03:13, 13 October 2007 (UTC)Reply

Mtidei, let us know when it's done and when there are no ads on it. Sorry I confused it with the .com site and used the vandalism button in my reverts, but as long as you're building a site with ads, I'll probably not see it so much as a "contribution" as a promotional effort for yourself. Dicklyon 05:02, 13 October 2007 (UTC)Reply

Re: Applet-picture looks nice but applet itself has problem: "Error: class Illumination not found"
Dear Wikicat, thanks for your feedback! Please tell me what jre version you use. I unfortunately could not reproduce the error on any pc. Does somebody see the same error? Mtidei 09:50, 19 October 2007 (UTC)Reply

Thanks for *your* feedback! V-1.4203 (w98!) =< ancient? If so, disregard problem report. :) PS: dup-msg on usr-tlk pg del-d Wikicat (temp-2k7) 00:10, 20 October 2007 (UTC)Reply

Java made a big step in version 1.5 (September 2004) and came with new language features I dont want to miss as a java developer. Versions prior to 1.5 are not able to compile the new constructs. I'll post a java update link on my site. Mtidei 01:12, 20 October 2007 (UTC)Reply

It says "candela (= lm/sr)". What does "sr" mean? (A wikilink might help here.) Thanks. ☺Coppertwig (talk) 16:14, 30 May 2009 (UTC)Reply

Steradian. It is wikilinked the first time it occurs.--Srleffler (talk) 02:31, 31 May 2009 (UTC)Reply

I have a set of photometry teaching notes which I prepared. A pdf, how do I place it here for discussion?RayJohnstone (talk) 12:38, 18 March 2011 (UTC)Reply

I think PDFs can be uploaded through the upload page, and then you could post a link to the uploaded file here. Be sure to read and follow the prompts for copyright and licensing info carefully. If it's not clear that you have the rights to the files and are licensing them for others to use, the file will get deleted.

I don't know if the rules allow uploading something like teaching notes, but you could give it a try and see if anybody complains. There is another project called Wikisource which is intended for academic media that aren't really encyclopedic in form. I don't know what that project's submission rules are, though. If you have a lot of material, you might want to look into it.--Srleffler (talk) 01:25, 19 March 2011 (UTC)Reply

Thanks for your suggertion, will try. The notes are my own work (interpretation).RayJohnstone (talk) 17:50, 22 March 2011 (UTC)Reply

Have done this, try http://en.wikipedia.org/wiki/File:Rays_photometry_0001.pdf RayJohnstone (talk) 00:35, 23 March 2011 (UTC)Reply

Either you didn't follow the prompts, or something went wrong during upload. There is no license tag, which will cause the file to be deleted. You can fix this. Edit the image page and replace the line "{{di-no license|date=23 March 2011}}" with one or both of:

• "{{GFDL-self}}"
• "{{Cc-by-sa|J.R.Johnstone}}"

These templates say that you are licensing the file for others to use under the GFDL and CC-by-SA licenses, respectively. You have other licensing options; these two are easy and commonly-used.--Srleffler (talk) 01:22, 23 March 2011 (UTC)Reply

I can't find the line "{{di-no license|date=23 March 2011}}" I assume the image page is that showing my notes as a pdf.RayJohnstone (talk) 02:52, 23 March 2011 (UTC)Reply

Click this link. It should open a Wikipedia edit window with the line in question at the top. Replace it with the template text I give above. Alternatively, if you say which license(s) you want, I can add it for you. I can't do this without your permission...--Srleffler (talk) 03:17, 24 March 2011 (UTC)Reply

Yes, please add for me, you have my permission to add the licence you see fit. — Preceding unsigned comment added by RayJohnstone (talk • contribs) 17:15, 27 March 2011 (UTC)Reply

Done.--Srleffler (talk) 22:17, 27 March 2011 (UTC)Reply

Thanks.If anyone wishes to incorporate some of these notes, please do so. I think they are good, but authors do think that wayRayJohnstone (talk) 14:40, 29 March 2011 (UTC).Reply

Regarding the image of the photopic peak (image is the yellow-green rectangle here: http://en.wikipedia.org/wiki/File:555nmPhotopicPeakMax.png ) in this article, with the caption "Color our daytime-adapted eyes are most sensitive to (max of the photopic peak)." Is this correct? I was under the impression that the sRGB colour space (the colour profile of the image) can't depict "true" 550nm green.

Assuming it's wrong, then it seems best to switch to an image with a wide-gamut colour profile (Adobe RGB probably, since it's one of the most common wide-gamut options for monitors) that at least comes somewhat closer to true monochromatic green, and throw down a disclaimer that the colour cannot be displayed properly, even on wide-gamut monitors.

--Wascally wabbit (talk) 20:56, 11 June 2011 (UTC)Reply

I removed the flawed image for now. I never thought it was very useful, and it's pretty much worthless if it's not a good approximation to the actual colour.--Srleffler (talk) 02:28, 12 June 2011 (UTC)Reply

I don't know how useful it is, but RGB color is pretty accurate in that region, even for sRGB, and in any case it can be said to be "The hue that our daytime-adapted eyes are most sensitive to (max of the photopic peak)" if we decide we want such a portrayal. It would be more interesting if contrasted with the hue of the scotopic peak. Dicklyon (talk) 16:55, 12 June 2011 (UTC)Reply

Whatever you all feel is best. I'd like to emphasize (since I somehow forgot to mention it earlier) that I'm a layperson, so I'm not certain how accurate my criticism of the image was. --Wascally wabbit (talk) 16:37, 17 June 2011 (UTC)Reply

The section "Photometric versus radiometric quantities" is not very well done. It offers little explanation and simply copies a large table entitled, "SI radiometry quantities" which is a straight copy from the page Radiometry. This section topic, while of symmetrical importance to the Radiometry page is not mentioned on the Radiometry page. I'm proposing a new page, entitled something like "Radiometry versus Photometry" be created that more accurately expresses the relation of these two fields. The reason a new page is better than adding it to one of them is the relation between the two topics truly is symmetric and should be linked to from each page. I will begin work on this in the coming days, and welcome comments. Alexmead (talk) 11:59, 28 July 2015 (UTC)Reply

Sounds like an interesting idea. Give it a try.--Srleffler (talk) 05:29, 29 July 2015 (UTC)Reply

This article and that on radiometry ought to include quantities describing material properties for eg reflexion, scattering, transmission and emission. In radiometry for example BRDF can be used to describe the relation between irradiance and radiance for a surface. BRDF is a multidimensional function describing a large range of conditions. There are probably other quantities of interest too, some relating other quantities to each other, some representing subsets of conditions.150.227.15.253 (talk) 15:37, 16 January 2024 (UTC)Reply

Sounds like a good idea. Why don't you add some information on that?--Srleffler (talk) 06:49, 17 January 2024 (UTC)Reply