Category: photography
Photography basics: Lumens vs Candelas (candle) vs Lux vs FootCandle vs Watts vs Irradiance vs Illuminance
https://www.translatorscafe.com/unit-converter/en-US/illumination/1-11/
The power output of a light source is measured using the unit of watts W. This is a direct measure to calculate how much power the light is going to drain from your socket and it is not relatable to the light brightness itself.
The amount of energy emitted from it per second. That energy comes out in a form of photons which we can crudely represent with rays of light coming out of the source. The higher the power the more rays emitted from the source in a unit of time.
Not all energy emitted is visible to the human eye, so we often rely on photometric measurements, which takes in account the sensitivity of human eye to different wavelenghts
https://pllight.com/understanding-lighting-metrics/
Candela is the basic unit of measure of light intensity from any point in a single direction from a light source. It measures the total volume of light within a certain beam angle and direction.
While the luminance of starlight is around 0.001 cd/m2, that of a sunlit scene is around 100,000 cd/m2, which is a hundred millions times higher. The luminance of the sun itself is approximately 1,000,000,000 cd/m2.
https://www.hdrsoft.com/resources/dri.html#bit-depth
To make it easier to represent values that vary so widely, it is common to use a logarithmic scale to plot the luminance. The scanline below represents the log base 10 of the luminance, so going from 0.1 to 1 is the same distance as going from 100 to 1000, for instance. A scene showing the interior of a room with a sunlit view outside the window, for instance, will have a dynamic range of approximately 100,000:1.
Lumen (lm) is the basic unit of measure for a light that is visible to the human eye. It indicates the total potential amount of light from a light source. If a uniform point source of 1 candela is at the center of a sphere with a 1ft2 radius with an opening of 1 ft2 at its surface, the quantity of light that passes through that opening is equal to 1 lumen. Since lumens are a photometric measurement for humans, we do not use this unit of measure for describing horticultural lighting.
Technically speaking, a Lumen is the SI unit of luminous flux, which is equal to the amount of light which is emitted per second in a unit solid angle of one steradian from a uniform source of one-candela intensity radiating in all directions.
Illuminance refers to the density of light over a given surface area, and is expressed in mostly LUX or lumens/m2.
Luminance refers to the amount of light emitted under various circumstances, and it is expressed mostly in LUMENS or candela/m2.
Lux (lx) or often Illuminance, is a photometric unit along a given area, which takes in account the sensitivity of human eye to different wavelenghts. It is the measure of light at a specific distance within a specific area at that distance. Often used to measure the incidental sun’s intensity. Its default unit describes the number of lumens visible in a square meter (lumen/m2). 100 lumens spread out over an area of 1 m2 will have an illuminance of 100 lx. The same 100 lumens spread out over 10 m2 produces a dimmer illuminance of only 10 lx.
The core difference between lux and lumens can be summarized as follows:
- Lux is a measure of illuminance, the total amount of light that falls on a surface at a given distance
- Lumens is a measure of luminous flux, the total amount of light emitted in all directions.
A footcandle describes the number of lumen per square foot. Therefore, one footcandle is equal to approximately 10.764 lx. This measure is only relevant for how we perceive light and is irrelevant for plant growth. Like lumens, lux and footcandles are not useful for describing horticultural lighting.
Color Rendering Index, or CRI, describes the ability of a light source to show an object’s color accurately in comparison to standardized colour samples under a reference light source. The highest value a light can achieve is a CRI of 100. Lower CRI values result in objects appearing unnatural or discolored. Under a light with a CRI of 100, an orange appears bright orange; under a light with a CRI of 70, the orange appears darker and bluer. This measure is dependent on how the human eye sees light, and so it is not a useful parameter for choosing horticultural lighting.
Correlated Color Temperature, or CCT, describes the color of a light source vs. a reference source when heated to a particular temperature, and is measured in degrees Kelvin (°K). The higher the CCT of a light source, the cooler the light’s color. For example, a very red light achieves a CCT of about 1000 K while a very blue light can achieve a CCT of about 10,000 K. Warm white lights will have a CCT around 2700 K (since they emit more energy at the red end of the spectrum), neutral white will be around 4000 K, and cool white around 5000 K (emitting more energy at the blue end of the spectrum). Similar to CRI, this measure is dependent on light perception by the human eye, and, once again, is not useful for describing or choosing horticultural lighting.
http://www.lumis.co.nz/reference-information/lighting-terminology
Light is a visible portion of electromagnetic radiation. Watts isn’t a measure of light output. Watts is actually a measure of total power output. Not all of the energy emitted by a light source is visible light – heat and invisible light waves (ex. infrared light) are also emitted. Lumens, on the other hand, will tell you the total visible light output of a source. For this reason, lumens (not watts) is the relevant unit of measure when you’re concerned about visibility. The higher the power the more rays emitted from the source in a unit of time.
Irradiance (radiant flux emitted by a surface per unit area aka watt per square meter) is a radiometric unit. As such also actually a measure of total power output.
Radiometric units are based on physical power, that means all wavelengths are weighted equally, while photometric units take into account the sensitivity of human eye to different wavelengths.
The weighting is determined by the luminosity function (which was measured for human eye and is an agreed-upon standard).
Converting Irradiance and Illuminance
http://www.dfisica.ubi.pt/~hgil/Fotometria/HandBook/ch07.html
There is a different conversion factor for every wavelength, so the spectral composition of light must be known to make the conversion.
At the most sensitive wavelegth to the human eye the conversion factor is
1.0 W/m2 = 683.002 lumen/m2 # at wavelength = 555nm (green)
That means the irradiance (power) to make 1 lumen is at it’s minimum at this wavelength (just 1.464 mW/m2).
Luminous efficiency is then the ratio between the actual number of lumens per watt and the theoretical maximum.
Incandescent light bulb has a luminous efficiency of 2% which is very poor. It’s because lot of it’s irradiance is only heat which is not visible. The luminosity function is zero for wavelengths outside the visible spectrum.
https://www.rapidtables.com/calc/light/lux-to-lumen-calculator.html
https://www.projectorpoint.co.uk/news/how-bright-should-my-projector-be/
https://dracobroadcast.eu/blogs/news/continuous-light-converting-guide
- Watts (halogen) – A measure of energy consumed
- Watts (HMI) – A measure of energy consumed
- Watts (LED) – A measure of energy consumed
- Lux – Lumens per square meter, illuminance at target
- Footcandles – Lumens per square foot
- Stops – Size of lens aperture
- EV – Exposure Value
- Lumens – Measure of amount of visible light, luminance from source
- Candela – Measure of entire volume of lighting
- NIT = Candela per square meter but is not part of the International System of Units
Photography basics: Production Rendering Resolution Charts
https://www.urtech.ca/2019/04/solved-complete-list-of-screen-resolution-names-sizes-and-aspect-ratios/
| Resolution – Aspect Ratio | 4:03 | 16:09 | 16:10 | 3:02 | 5:03 | 5:04 |
| CGA | 320 x 200 | |||||
| QVGA | 320 x 240 | |||||
| VGA (SD, Standard Definition) | 640 x 480 | |||||
| NTSC | 720 x 480 | |||||
| WVGA | 854 x 450 | |||||
| WVGA | 800 x 480 | |||||
| PAL | 768 x 576 | |||||
| SVGA | 800 x 600 | |||||
| XGA | 1024 x 768 | |||||
| not named | 1152 x 768 | |||||
| HD 720 (720P, High Definition) | 1280 x 720 | |||||
| WXGA | 1280 x 800 | |||||
| WXGA | 1280 x 768 | |||||
| SXGA | 1280 x 1024 | |||||
| not named (768P, HD, High Definition) | 1366 x 768 | |||||
| not named | 1440 x 960 | |||||
| SXGA+ | 1400 x 1050 | |||||
| WSXGA | 1680 x 1050 | |||||
| UXGA (2MP) | 1600 x 1200 | |||||
| HD1080 (1080P, Full HD) | 1920 x 1080 | |||||
| WUXGA | 1920 x 1200 | |||||
| 2K | 2048 x (any) | |||||
| QWXGA | 2048 x 1152 | |||||
| QXGA (3MP) | 2048 x 1536 | |||||
| WQXGA | 2560 x 1600 | |||||
| QHD (Quad HD) | 2560 x 1440 | |||||
| QSXGA (5MP) | 2560 x 2048 | |||||
| 4K UHD (4K, Ultra HD, Ultra-High Definition) | 3840 x 2160 | |||||
| QUXGA+ | 3840 x 2400 | |||||
| IMAX 3D | 4096 x 3072 | |||||
| 8K UHD (8K, 8K Ultra HD, UHDTV) | 7680 x 4320 | |||||
| 10K (10240×4320, 10K HD) | 10240 x (any) | |||||
| 16K (Quad UHD, 16K UHD, 8640P) | 15360 x 8640 |
Photography basics: Solid Angle measures
http://www.calculator.org/property.aspx?name=solid+angle
A measure of how large the object appears to an observer looking from that point. Thus. A measure for objects in the sky. Useful to retuen the size of the sun and moon… and in perspective, how much of their contribution to lighting. Solid angle can be represented in ‘angular diameter’ as well.
http://en.wikipedia.org/wiki/Solid_angle
http://www.mathsisfun.com/geometry/steradian.html
A solid angle is expressed in a dimensionless unit called a steradian (symbol: sr). By default in terms of the total celestial sphere and before atmospheric’s scattering, the Sun and the Moon subtend fractional areas of 0.000546% (Sun) and 0.000531% (Moon).
http://en.wikipedia.org/wiki/Solid_angle#Sun_and_Moon
On earth the sun is likely closer to 0.00011 solid angle after athmospheric scattering. The sun as perceived from earth has a diameter of 0.53 degrees. This is about 0.000064 solid angle.
http://www.numericana.com/answer/angles.htm
The mean angular diameter of the full moon is 2q = 0.52° (it varies with time around that average, by about 0.009°). This translates into a solid angle of 0.0000647 sr, which means that the whole night sky covers a solid angle roughly one hundred thousand times greater than the full moon.
More info
http://lcogt.net/spacebook/using-angles-describe-positions-and-apparent-sizes-objects
http://amazing-space.stsci.edu/glossary/def.php.s=topic_astronomy
Angular Size
The apparent size of an object as seen by an observer; expressed in units of degrees (of arc), arc minutes, or arc seconds. The moon, as viewed from the Earth, has an angular diameter of one-half a degree.
The angle covered by the diameter of the full moon is about 31 arcmin or 1/2°, so astronomers would say the Moon’s angular diameter is 31 arcmin, or the Moon subtends an angle of 31 arcmin.
Brett Jones / Phil Reyneri (Lightform) / Philipp7pc: The study of Projection Mapping through Projectors
Video Projection Tool Software
https://hcgilje.wordpress.com/vpt/
https://www.projectorpoint.co.uk/news/how-bright-should-my-projector-be/
http://www.adwindowscreens.com/the_calculator/
heavym
https://heavym.net/en/
MadMapper
https://madmapper.com/
3D Photography using Context-aware Layered Depth Inpainting
venturebeat.com/2020/05/25/ai-researchers-say-they-created-a-better-way-to-generate-3d-photos/
https://shihmengli.github.io/3D-Photo-Inpainting/
https://app.wandb.ai/authors/3D-Inpainting/reports/3D-Image-Inpainting--VmlldzoxNzIwNTY
https://github.com/vt-vl-lab/3d-photo-inpainting
https://colab.research.google.com/drive/1706ToQrkIZshRSJSHvZ1RuCiM__YX3Bz
Shutter.Pixelsham.com
Introducing shutter.pixelsham.com/
