![]() | This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
I added illumination use, because light meters are very often used in automatic regulation of lighting.
There is, however, a question of combining different articles related to that: 'PIN diode' or 'light regulation', which is currently, quite unappropriately, redirected to 'Dark-sky movement' article
Mitjaprelovsek 16:56, 29 April 2006 (UTC)
I added the math to this section in attempt to show the basis for readings obtained with a neutral test card. Almost as this was added, however, it struck me as adding more clutter than utility. Unless someone objects, I'm inclined to remove it. Thoughts? JeffConrad 22:41, 15 October 2006 (UTC)
A minor note: the remainder of the article is in American English, so I think "analog" might be preferable to "analogue". There are far greater issues, though; this article has had many contributors, and it reads as a bit of a hodgepodge. It would benefit considerably from an overall edit. JeffConrad 00:24, 17 March 2007 (UTC)
This article could use a lot of work. Much more needed about the history of light meters. How well the various sensors/instruments cover how wide a range of lighting levels. Typical costs. Much more about non-photography uses of light meters, in lighting design and test, scientific uses. Links to such sources.- 69.87.204.232 12:37, 19 May 2007 (UTC)
How does one actually measure lumens?- 69.87.204.232 12:37, 19 May 2007 (UTC)
Lighting manufacturers use a goniophotometer, which is a mirror on a robotic arm that bounces light into a sensor. Measurements are taken at regular intervals around the lamp or fixture, and the lumen output for a given steridian is then calculated. That's my understanding, anyway. I agree that this could be expanded upon. Ohnoezitasploded ( talk) 03:59, 2 October 2010 (UTC)
Lux is the unit of measure most often used to measure light. (The USA still measure in foot-candle*, 2500lux = 26900 foot-candle). Here are some typical lux figures: [1]
- 69.87.204.232 13:39, 19 May 2007 (UTC)
Plant growing light meters are readily available, starting at about $20 USD online:
Hydrofarm Light Meter
"This Hydrofarm Plant Light Intensity Meter is an easy and accurate way to measure natural, fluorescent, or HID light for gardening use. With a range from 0 - 5000 foot-candles you can monitor your lamp's intensity for seasonal light changes in your home. HF's Light Meter is permanently calibrated, accurate to 2%, and requires no batteries. Also includes a booklet with optimum footcandles for a variety of plants."
[2]
[3]
Rapitest Moisture/Light Meter
"Manufacturer: Luster Leaf (#1830)
UPC: 035307018304
Retail: $19.99
The ultimate tool for measuring two of the most important elements for healthy plants - light and water. Instantly switches from moisture to light meter. No batteries required."
[4]
-
69.87.204.232
13:51, 19 May 2007 (UTC)
Industrial & Commercial Grade Precision Light Meters, including Footcandle Meters, Lux Meters and UV (UltraViolet) Meters $50-150 [5]
LX-1010B
Economic Lux meter ever made
$40 USD
Specifications:
To check the level of bright
Range:0- 2,000/20,000/ 50,000 Lux (+-5%+2D)
Accuracy: 5.0%
Resolution: 1 Lux
Sampling time:0.4 second
Dimensions:
Body: 4.6 X 2.7 X 1.10"
Sensor: 3.26 X 2 X0.8"
Weight : 160 g.
Measure 0 -- 50,000 lux for a wide range of use.
Ideal for use by architectures, light designers, and photographers..
Weight: (Lbs) 0.36LB
[6]
-
69.87.203.79
17:31, 19 May 2007 (UTC)
International Light made scientific radiometers, and they have now merged with Gilway, in Massachusetts US. Specialized units called "belt monitors" are sold for monitoring UV curing facilities. This page has a number of detailed radiometer detector spectral curves, from 200-2000 nm. [7] It would be great to have details about photo detectors of various types in WP.- 69.87.203.9 11:55, 30 May 2007 (UTC)
Is it right to remove the comment about the consistency of incident-light measurements? Although I question whether they are more precise (or more "correct"), I think they usually are more consistent than reflected-light measurements of a given scene. It might be helpful to hear from a cinematographer on this. JeffConrad 21:09, 26 May 2007 (UTC)
According to this article, the ISO film speed S is given by S=Kn^2/Lt, where L is the luminance of a medium-brightness area (candela/m^2), n the aperture number, K a constant (usually between 12 and 14), and t is the shutter speed. Usually, medium brightness is taken to be an 18% reflective card. However, this doesn't say anything about the headroom. Should a sensor with a given ISO number be at exactly 18% of saturation for a given luminance L? Or is there a standard amount of headroom? I've searched a bit and I found numbers of 106%, 170%, and 141% for the saturation level. What does the ISO document say about it? This information seems to be missing. See e.g. [8], [9], [10]. Han-Kwang ( t) 15:21, 10 October 2007 (UTC)
I see, so the equation n^2/t = LS/K is a simply a definition of what the reading that a light meter should produce for a given luminance, even though K is somewhat variable. But as a photographer, of course I would want to know how much headroom I will get if I point the light meter at a 18% card. As you say, officially the saturation level should be 141% (1/2 stop above 100%), but in practice YMMV (e.g. my digital compact camera seems to aim for 18/100 rather than 18/141). Maybe this subject really belongs on film speed, where I also asked this question. Anyway, I think the focal plane exposure is given by H=pi L t/4 n^2 (for objects far away from the lens), so Ssat = 78/Hs = 312 n^2/ (pi*Lsat*t) where Lsat is the luminosity that just saturates the sensor. I guess that 78 comes from 100*pi/4, so Ssat=100 n^2/(Lsat*t), which seems to be an elegant equation -- would it be appropriate to mention on film speed? Han-Kwang ( t) 23:43, 10 October 2007 (UTC)
I wonder if the paragraph on spectral sensitivity (near the bottom of the section Use in photography) isn't a bit misleading, for two reasons:
What constitutes a “good match” is somewhat subjective; if it means essentially that most meters recommend reasonably acceptable exposures most of the the time, then the match probably is good in most cases. But various meters have wildly differing spectral responses. For example, Pentax spotmeters have very broad response, extending from slightly into UV to well into IR; Kenko (formerly Minolta) have rather narrow response, approximately that of the 1931 CIE photopic observer. In many cases, reasonable results can be obtained with either meter, although relative readings change a bit when measuring objects of different colors. In extreme situations, the differences can be astounding. For example, in a yellow-light room used for semiconductor photolithography, I have seen indications by Pentax and Minolta meters differ by 5 EV; presumably, at least one was incorrect ...
Correcting the response by filtration may work quite well on a meter with broad spectral response, but is less effective on a meter whose built-in filtration already attenuates the response in the region of interest for a particular film.
Much time and effort has been expended in numerous forums arguing about differences in nominal calibration among various manufacturers and about alleged “18% calibration” vs. “12% calibration,” but either difference is often small in comparison with differences in spectral sensitivity. JeffConrad ( talk) 19:58, 6 February 2008 (UTC)
In the formulae for Light_meter#Calibrated_reflectance, would it be appropriate to replace with for consistency with reflectance or R for consistency with Reflection_coefficient#Optics ? -- Redbobblehat ( talk) 17:51, 5 February 2009 (UTC)
The mention of an integrating sphere isn't really correct, for two reasons:
The function of the receptor isn't important in this context; what matter is the incident-light measurement's independence of the reflectance of scene elements. The function of the hemispherical receptor is adequately (and accurately) explained in the section Calibration constants.
I'm going to remove this sentence unless someone has a good reason for keeping it. JeffConrad ( talk) 04:52, 9 February 2009 (UTC)
Perhaps a section headed Angle of acceptance would be a useful starting point for comparing the practical (and mathematical? ;) differences between "dome" & "flat" incident meters, and "spot" and "matrix average" (or whatever) reflected meters ? I'm thinking that even if angle of acceptance isn't the only factor involved, it could be a helpful 'backbone' for structuring the other factors around; a good place to start for the uninitiated reader ? --
Redbobblehat (
talk)
14:45, 9 February 2009 (UTC)
I have learned that Thomas Edison, the inventor of photography, invented the light meter too. Unfortunately, I've got no reliable references, can anyone help? -- 141.91.129.2 ( talk) 09:32, 21 August 2009 (UTC)
The units don't work out on the equation for a light meter . . . this is strange i am curious what the real formula is 128.197.81.26 ( talk) 00:01, 16 January 2010 (UTC)
There remains perpetual confusion on many photography blogs regarding the above. I think the section Light_Meter#Calibrated_reflectance answers it in part (and yet they still argue). I think it might be easier for lay readers to get their heads around it if we explain that by converting the image into a jpeg or tiff - the noise is simply removed - and this creates a pseudo Ev reduction. Thus making it appear that the light-meter (either built-in or hand-held) is calibrated to ≈18%. The footnote on page 11 of The ISO Definition of the Dynamic Range of a Digital Still Camera, Douglas Kerr makes this easy to understand when explaining noise removal– without the math. Quote:
“It is this margin provision that causes the confusion between the roles of an 18% average reflectance and a 13% average scene
reflectance as premises for the “standard” exposure meter calibration; the luminance that is 18% of “70.1% of maximum
recordable luminance” is 13% of the maximum recordable luminance itself.”
However, this Wikipedia article is about light meters only and not cameras and what happens to the RAW image data. So I'm not sure how to add this information to the article. I have just looked at the Sekonic L-208 TwinMate specs on their site. They quote: C = 340 and K = 12·5. So, (π*12.5)/340 = 0·1155 or 11·6% if you like. Well within the ISO specifications. Yet converted a RAW file exposed with the help of this instrument to jpeg or tiff and a pseudo change in mid tone will appear as if the camera was calibrated to about 18% (give or take 1/3 of a stop (as allowed in the ISO std for jpegs and tiffs). Have also found a sketch of how to use a grey card properly. [15]. One is aiming for diffuse reflection not specular reflection (which the often quoted angle of 45° will encourage). Also, the card will appear about 1/3 stop dimmer. That together with the ≈ -1/3 stop most digital cameras appear to meter, from a grey card full-on and the Ev will be about right for most shots. I'm hopeless at drawing but if you think it would be useful here and on Grey card I will issue a request on WP for a drawing to be done. After all, the idea itself is not copyrightable although this image is.-- Aspro ( talk) 02:25, 6 December 2014 (UTC)
![]() | This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
I added illumination use, because light meters are very often used in automatic regulation of lighting.
There is, however, a question of combining different articles related to that: 'PIN diode' or 'light regulation', which is currently, quite unappropriately, redirected to 'Dark-sky movement' article
Mitjaprelovsek 16:56, 29 April 2006 (UTC)
I added the math to this section in attempt to show the basis for readings obtained with a neutral test card. Almost as this was added, however, it struck me as adding more clutter than utility. Unless someone objects, I'm inclined to remove it. Thoughts? JeffConrad 22:41, 15 October 2006 (UTC)
A minor note: the remainder of the article is in American English, so I think "analog" might be preferable to "analogue". There are far greater issues, though; this article has had many contributors, and it reads as a bit of a hodgepodge. It would benefit considerably from an overall edit. JeffConrad 00:24, 17 March 2007 (UTC)
This article could use a lot of work. Much more needed about the history of light meters. How well the various sensors/instruments cover how wide a range of lighting levels. Typical costs. Much more about non-photography uses of light meters, in lighting design and test, scientific uses. Links to such sources.- 69.87.204.232 12:37, 19 May 2007 (UTC)
How does one actually measure lumens?- 69.87.204.232 12:37, 19 May 2007 (UTC)
Lighting manufacturers use a goniophotometer, which is a mirror on a robotic arm that bounces light into a sensor. Measurements are taken at regular intervals around the lamp or fixture, and the lumen output for a given steridian is then calculated. That's my understanding, anyway. I agree that this could be expanded upon. Ohnoezitasploded ( talk) 03:59, 2 October 2010 (UTC)
Lux is the unit of measure most often used to measure light. (The USA still measure in foot-candle*, 2500lux = 26900 foot-candle). Here are some typical lux figures: [1]
- 69.87.204.232 13:39, 19 May 2007 (UTC)
Plant growing light meters are readily available, starting at about $20 USD online:
Hydrofarm Light Meter
"This Hydrofarm Plant Light Intensity Meter is an easy and accurate way to measure natural, fluorescent, or HID light for gardening use. With a range from 0 - 5000 foot-candles you can monitor your lamp's intensity for seasonal light changes in your home. HF's Light Meter is permanently calibrated, accurate to 2%, and requires no batteries. Also includes a booklet with optimum footcandles for a variety of plants."
[2]
[3]
Rapitest Moisture/Light Meter
"Manufacturer: Luster Leaf (#1830)
UPC: 035307018304
Retail: $19.99
The ultimate tool for measuring two of the most important elements for healthy plants - light and water. Instantly switches from moisture to light meter. No batteries required."
[4]
-
69.87.204.232
13:51, 19 May 2007 (UTC)
Industrial & Commercial Grade Precision Light Meters, including Footcandle Meters, Lux Meters and UV (UltraViolet) Meters $50-150 [5]
LX-1010B
Economic Lux meter ever made
$40 USD
Specifications:
To check the level of bright
Range:0- 2,000/20,000/ 50,000 Lux (+-5%+2D)
Accuracy: 5.0%
Resolution: 1 Lux
Sampling time:0.4 second
Dimensions:
Body: 4.6 X 2.7 X 1.10"
Sensor: 3.26 X 2 X0.8"
Weight : 160 g.
Measure 0 -- 50,000 lux for a wide range of use.
Ideal for use by architectures, light designers, and photographers..
Weight: (Lbs) 0.36LB
[6]
-
69.87.203.79
17:31, 19 May 2007 (UTC)
International Light made scientific radiometers, and they have now merged with Gilway, in Massachusetts US. Specialized units called "belt monitors" are sold for monitoring UV curing facilities. This page has a number of detailed radiometer detector spectral curves, from 200-2000 nm. [7] It would be great to have details about photo detectors of various types in WP.- 69.87.203.9 11:55, 30 May 2007 (UTC)
Is it right to remove the comment about the consistency of incident-light measurements? Although I question whether they are more precise (or more "correct"), I think they usually are more consistent than reflected-light measurements of a given scene. It might be helpful to hear from a cinematographer on this. JeffConrad 21:09, 26 May 2007 (UTC)
According to this article, the ISO film speed S is given by S=Kn^2/Lt, where L is the luminance of a medium-brightness area (candela/m^2), n the aperture number, K a constant (usually between 12 and 14), and t is the shutter speed. Usually, medium brightness is taken to be an 18% reflective card. However, this doesn't say anything about the headroom. Should a sensor with a given ISO number be at exactly 18% of saturation for a given luminance L? Or is there a standard amount of headroom? I've searched a bit and I found numbers of 106%, 170%, and 141% for the saturation level. What does the ISO document say about it? This information seems to be missing. See e.g. [8], [9], [10]. Han-Kwang ( t) 15:21, 10 October 2007 (UTC)
I see, so the equation n^2/t = LS/K is a simply a definition of what the reading that a light meter should produce for a given luminance, even though K is somewhat variable. But as a photographer, of course I would want to know how much headroom I will get if I point the light meter at a 18% card. As you say, officially the saturation level should be 141% (1/2 stop above 100%), but in practice YMMV (e.g. my digital compact camera seems to aim for 18/100 rather than 18/141). Maybe this subject really belongs on film speed, where I also asked this question. Anyway, I think the focal plane exposure is given by H=pi L t/4 n^2 (for objects far away from the lens), so Ssat = 78/Hs = 312 n^2/ (pi*Lsat*t) where Lsat is the luminosity that just saturates the sensor. I guess that 78 comes from 100*pi/4, so Ssat=100 n^2/(Lsat*t), which seems to be an elegant equation -- would it be appropriate to mention on film speed? Han-Kwang ( t) 23:43, 10 October 2007 (UTC)
I wonder if the paragraph on spectral sensitivity (near the bottom of the section Use in photography) isn't a bit misleading, for two reasons:
What constitutes a “good match” is somewhat subjective; if it means essentially that most meters recommend reasonably acceptable exposures most of the the time, then the match probably is good in most cases. But various meters have wildly differing spectral responses. For example, Pentax spotmeters have very broad response, extending from slightly into UV to well into IR; Kenko (formerly Minolta) have rather narrow response, approximately that of the 1931 CIE photopic observer. In many cases, reasonable results can be obtained with either meter, although relative readings change a bit when measuring objects of different colors. In extreme situations, the differences can be astounding. For example, in a yellow-light room used for semiconductor photolithography, I have seen indications by Pentax and Minolta meters differ by 5 EV; presumably, at least one was incorrect ...
Correcting the response by filtration may work quite well on a meter with broad spectral response, but is less effective on a meter whose built-in filtration already attenuates the response in the region of interest for a particular film.
Much time and effort has been expended in numerous forums arguing about differences in nominal calibration among various manufacturers and about alleged “18% calibration” vs. “12% calibration,” but either difference is often small in comparison with differences in spectral sensitivity. JeffConrad ( talk) 19:58, 6 February 2008 (UTC)
In the formulae for Light_meter#Calibrated_reflectance, would it be appropriate to replace with for consistency with reflectance or R for consistency with Reflection_coefficient#Optics ? -- Redbobblehat ( talk) 17:51, 5 February 2009 (UTC)
The mention of an integrating sphere isn't really correct, for two reasons:
The function of the receptor isn't important in this context; what matter is the incident-light measurement's independence of the reflectance of scene elements. The function of the hemispherical receptor is adequately (and accurately) explained in the section Calibration constants.
I'm going to remove this sentence unless someone has a good reason for keeping it. JeffConrad ( talk) 04:52, 9 February 2009 (UTC)
Perhaps a section headed Angle of acceptance would be a useful starting point for comparing the practical (and mathematical? ;) differences between "dome" & "flat" incident meters, and "spot" and "matrix average" (or whatever) reflected meters ? I'm thinking that even if angle of acceptance isn't the only factor involved, it could be a helpful 'backbone' for structuring the other factors around; a good place to start for the uninitiated reader ? --
Redbobblehat (
talk)
14:45, 9 February 2009 (UTC)
I have learned that Thomas Edison, the inventor of photography, invented the light meter too. Unfortunately, I've got no reliable references, can anyone help? -- 141.91.129.2 ( talk) 09:32, 21 August 2009 (UTC)
The units don't work out on the equation for a light meter . . . this is strange i am curious what the real formula is 128.197.81.26 ( talk) 00:01, 16 January 2010 (UTC)
There remains perpetual confusion on many photography blogs regarding the above. I think the section Light_Meter#Calibrated_reflectance answers it in part (and yet they still argue). I think it might be easier for lay readers to get their heads around it if we explain that by converting the image into a jpeg or tiff - the noise is simply removed - and this creates a pseudo Ev reduction. Thus making it appear that the light-meter (either built-in or hand-held) is calibrated to ≈18%. The footnote on page 11 of The ISO Definition of the Dynamic Range of a Digital Still Camera, Douglas Kerr makes this easy to understand when explaining noise removal– without the math. Quote:
“It is this margin provision that causes the confusion between the roles of an 18% average reflectance and a 13% average scene
reflectance as premises for the “standard” exposure meter calibration; the luminance that is 18% of “70.1% of maximum
recordable luminance” is 13% of the maximum recordable luminance itself.”
However, this Wikipedia article is about light meters only and not cameras and what happens to the RAW image data. So I'm not sure how to add this information to the article. I have just looked at the Sekonic L-208 TwinMate specs on their site. They quote: C = 340 and K = 12·5. So, (π*12.5)/340 = 0·1155 or 11·6% if you like. Well within the ISO specifications. Yet converted a RAW file exposed with the help of this instrument to jpeg or tiff and a pseudo change in mid tone will appear as if the camera was calibrated to about 18% (give or take 1/3 of a stop (as allowed in the ISO std for jpegs and tiffs). Have also found a sketch of how to use a grey card properly. [15]. One is aiming for diffuse reflection not specular reflection (which the often quoted angle of 45° will encourage). Also, the card will appear about 1/3 stop dimmer. That together with the ≈ -1/3 stop most digital cameras appear to meter, from a grey card full-on and the Ev will be about right for most shots. I'm hopeless at drawing but if you think it would be useful here and on Grey card I will issue a request on WP for a drawing to be done. After all, the idea itself is not copyrightable although this image is.-- Aspro ( talk) 02:25, 6 December 2014 (UTC)