Talk:Photometry (optics)

message: Perhaps a confidence-inspiring reference could be found in E F Schubert's "Light Emitting Diodes" textbook. I am new to Wiki editing, but would be happy to help improve this article. If you have contributed significantly to this page, please let me know if there's anything you'd like done. -Parthi S, a career exergy conservationist (talk) 10:12, 18 November 2015 (UTC)
replies: text: If you see an area you can improve, jump in and give it a try. Other editors will help copyedit your work.--Srleffler (talk) 05:41, 19 November 2015 (UTC)
thread_title: References

message: <DT>Apostilb
<DD>Author of the Epistilbs
<DT>Bouguer's Law
<DD>Formula expressing the relationship between mucosal viscosity and Young's
modulus of elasticity of spherical boli formed by evaporative condensation
under conditions of rhinitis.
<DT>Bunsen Photometer
<DD>Device for eliminating grease stains from fast-food hamburger wrappers
by placing a source of illumination of the right intensity within the wrapper.
<DT>Candelabra
<DD>Unit of liberance. The standard candelabra is defined as the reflectance
of 88.00 standard ivories.
<DT>CIA standard chromaticity diagram
<DD>Used for graphic representation of shades of red and pink.
<DT>Conversion of units
<DD>There is no way to convert any photometric unit to any other photometric
unit. Deal with it.
<DT>Erectance
<DD>Unit of voluptuous excitance.
<DT>Eructance
<DD>Unit of reflux frequency. See also "ruminous flux."
<DT>Footlambent
<DD>Unit of podial luster.
<DT>Foot-camembert
<DD>Osmotic odorance of one standard foot incubated for 100 hours at 37
degrees centigrade. See also the metric unit, lox.
<DT>Infrared radiation
<DD>Red portion of the roast beef spectrum, transitioning at longer wavelengths
into the infmediumed (brown) and infwelldoned (grey) portions of the spectrum.
<DT>Lox
<DD>Osmotic odorance of one standard smoked salmonella incubated for 100
hours at 37 degrees centigrade. See also: foot-camembert, tallow rendering
index.
<DT>Luminary
<DD>Device for delivering a controlled amount of properly directed celebrity.
<DT>Nanometer
<DD>Photometric instrument used on the planet Ork. 
<DT>Nit
<DD>unit of capillate verminosity equal to one phthirapterum per follicle.
<DT>Numinance
<DD>Unit of directional light from above.
<DT>Ruminous flux
<DD>Unit of bovine regurgitance. See also eructance.
<DT>Steroidian
<DD>Unit of solid anger. Eight pi steroidians = a quantity of solid anger
equivalent to two balls.
<DT>Tallow rendering index
<DD>A light source is said to have a tallow rendering index of 100% if
it produces smoke of the same aroma as one standard candle.
<DT>Torchere
<DD>See: tormentor light.
<DT>Ultraviolent radiation
<DD>Radiation of suitable wavelength and intensity for denaturing the proteins
in human skin, disrupting the DNA in bacteria, and tearing oxygen molecules
viciously apart at the seams.
</DL>
P. S. Joke. Funny. Ha ha. Do not insert this material into any article.
--->  :-)  <---
Note smiley. Dpbsmith 02:09, 20 Jun 2004 (UTC)
thread_title: Photometric units

message: "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)
thread_title:  Visible watts 

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

message: 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)
replies: text: A. No, but it will appear somewhat brighter. The eye can detect an increase or decrease in light only when its intensity is doubled.
-69.87.203.48 19:57, 19 May 2007 (UTC)

text: 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)
thread_title:  Human eye 

message: 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)
thread_title:  Photopic Luminous Efficiency Function 

message: "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."
"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)
thread_title:  convert footcandles and lux to candelas 

message: 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)
thread_title:  near-field vs. far-field 

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

message: This page has a number of detailed radiometer detector spectral curves, from 200-2000 nm.  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)
thread_title:  photo detectors 

message: It says "candela (= lm/sr)". What does "sr" mean?  (A wikilink might help here.) Thanks. ☺Coppertwig (talk) 16:14, 30 May 2009 (UTC)
replies: text: Steradian. It is wikilinked the first time it occurs.--Srleffler (talk) 02:31, 31 May 2009 (UTC)
thread_title:  Excuse me, sr 

message: 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)
replies: text: 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)
replies: text: 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)
replies: text: 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)
thread_title:  Depiction of phototopic peak 

message: 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)
replies: text: Sounds like an interesting idea. Give it a try.--Srleffler (talk) 05:29, 29 July 2015 (UTC)
thread_title:  Photometric versus radiometric quantities 

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