Talk:Photometry (optics)

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Contents 1 Photometric units 2 Visible watts 3 Reflectivity 4 Human eye 4.1 Photopic Luminous Efficiency Function 5 convert footcandles and lux to candelas 6 near-field vs. far-field 7 Formulas 8 photo detectors 9 Photometry Applet / Calculator & Visualisation

[edit] Photometric units

Apostilb

Author of the Epistilbs

Bouguer's Law

Formula expressing the relationship between mucosal viscosity and Young's modulus of elasticity of spherical boli formed by evaporative condensation under conditions of rhinitis.

Bunsen Photometer

Device for eliminating grease stains from fast-food hamburger wrappers by placing a source of illumination of the right intensity within the wrapper.

Candelabra

Unit of liberance. The standard candelabra is defined as the reflectance of 88.00 standard ivories.

CIA standard chromaticity diagram

Used for graphic representation of shades of red and pink.

Conversion of units

There is no way to convert any photometric unit to any other photometric unit. Deal with it.

Erectance

Unit of voluptuous excitance.

Eructance

Unit of reflux frequency. See also "ruminous flux."

Footlambent

Unit of podial luster.

Foot-camembert

Osmotic odorance of one standard foot incubated for 100 hours at 37 degrees centigrade. See also the metric unit, lox.

Infrared radiation

Red portion of the roast beef spectrum, transitioning at longer wavelengths into the infmediumed (brown) and infwelldoned (grey) portions of the spectrum.

Lox

Osmotic odorance of one standard smoked salmonella incubated for 100 hours at 37 degrees centigrade. See also: foot-camembert, tallow rendering index.

Luminary

Device for delivering a controlled amount of properly directed celebrity.

Nanometer

Photometric instrument used on the planet Ork.

Nit

unit of capillate verminosity equal to one phthirapterum per follicle.

Numinance

Unit of directional light from above.

Ruminous flux

Unit of bovine regurgitance. See also eructance.

Steroidian

Unit of solid anger. Eight pi steroidians = a quantity of solid anger equivalent to two balls.

Tallow rendering index

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.

Torchere

See: tormentor light.

Ultraviolent radiation

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.

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

--->  :-) <---

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

[edit] Visible watts

"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)

[edit] Reflectivity

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

[edit] Human eye

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)

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)

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)

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)

[edit] Photopic Luminous Efficiency Function

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)

[edit] convert footcandles and lux to candelas

"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)

[edit] near-field vs. far-field

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)

[edit] Formulas

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)

[edit] photo detectors

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)

[edit] Photometry Applet / Calculator & Visualisation

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)

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)

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)

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)

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)

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)