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Experience with "Work Lights" used for Photography?
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Jul 6, 2020 09:38:06   #
DirtFarmer Loc: Escaped from the NYC area, back to MA
 
burkphoto wrote:
... fluorescent tubes, sodium vapor lamps, mercury vapor lamps, halogen metal iodide (HMI) lamps, high intensity discharge (HID) lamps, electronic flash, and LED lamps all produce *discontinuous* spectra. Some or many frequencies of the visible spectrum are missing entirely from their output, which makes it difficult to produce all the colors our eyes and cameras expect to see. Despite the custom, manual, or preset white balance or a Color Checker Passport, without some of these frequencies, or with too much energy at other frequencies, certain colors will appear brighter, dimmer, or different from what we should expect to see.
... fluorescent tubes, sodium vapor lamps, mercury... (show quote)


When I was working at UPittsburgh we had a stairway that was lit by low pressure sodium lamps. These lamps put out two spectral lines close together, making essentially a single color, yellow, that is probably more than 90% of the total energy output in the visible spectrum. In effect, when you entered the stairway everything was black and yellow. After a couple months my eyes got used to that and I started to see things in black and white. An interesting example of the brain's adaptability to the difference between expectation and reality.

However, our cameras and computer monitors don't have that adaptability and if I had taken a photo of the stairway, it would forever remain black and yellow (discounting the possibility of postprocessing, with which I could have made it black and white).

The spectra presented below show different light sources. These are approximations to reality since to some extent they will vary. The spectrum of sunlight for example will change depending on environmental conditions (think about red sunsets). Incandescent lamp spectra depend on the temperature. CFL spectra will depend on the phosphors used in the lamp. And LED spectra will depend on the specific semiconductor elements used in the LED (which is why LED lamps come in what they call "daylight", "cool white", "warm white", and "soft white").

But the point is that they all have different shapes. That means that there are colors in the LED spectrum that are significantly lower than the colors in sunlight, which has to be the standard against which we compare spectra, just because our eyes have evolved with only that spectrum to illuminate things. (Fire will be similar to incandescent lighting, but during most of our evolution, things were only illuminated by the sun). In particular, the figure below shows a dip in the LED spectrum just around 450nm.

That means there are colors that an LED lamp will not show well. OTOH, your camera detects and your computer monitor displays only 3 "colors". These colors are not narrow lines like the spikes you see in the CFL spectrum, but more like broad bumps in the spectrum. Essentially a color range. And they overlap. So the whole process is an approximation of an approximation.

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https://www.led-professional.com/resources-1/articles/led-light-spectrum-enhancement-with-transparent-pigmented-glazes-by-light-spectrum-glazes/screen-shot-2016-06-20-at-15-39-21.png/@@images/4855fd0f-4ac8-4357-941d-2b1663773c39.png
https://www.led-professional.com/resources-1/artic...
(Download)

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Jul 6, 2020 10:02:31   #
saside Loc: live in pueblo co
 
AKA A riddle wrapped in an enigma? Nice post, thank you. Now where is my ir sunglasses?

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Jul 11, 2020 11:00:10   #
JD750 Loc: SoCal
 
burkphoto wrote:
In practice, this is about what I've seen. The sun and incandescent bulbs are continuous spectra sources. They have SOME energy across the visible spectrum at all frequencies. Our eyes are tuned to the sun. But they adapt easily to about 3200K incandescent, and okay at 2700K incandescent. A custom, preset, or manual white balance using a reference target can do a great job of neutralizing any spectral differences and revealing most colors very accurately. A profile made with an X-Rite Color Checker Passport can do a REALLY good job getting it right.

However, fluorescent tubes, sodium vapor lamps, mercury vapor lamps, halogen metal iodide (HMI) lamps, high intensity discharge (HID) lamps, electronic flash, and LED lamps all produce *discontinuous* spectra. Some or many frequencies of the visible spectrum are missing entirely from their output, which makes it difficult to produce all the colors our eyes and cameras expect to see. Despite the custom, manual, or preset white balance or a Color Checker Passport, without some of these frequencies, or with too much energy at other frequencies, certain colors will appear brighter, dimmer, or different from what we should expect to see.
In practice, this is about what I've seen. The sun... (show quote)


Frequencies are missing!! Of course! Smack forehead. THAT explains why I can't get the WB right using some types of light. Thank you for that.

Maybe it also explains why I find LED lighting unpleasant to my eyes.

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Jul 11, 2020 19:15:29   #
burkphoto Loc: High Point, NC
 
JD750 wrote:
Frequencies are missing!! Of course! Smack forehead. THAT explains why I can't get the WB right using some types of light. Thank you for that.

Maybe it also explains why I find LED lighting unpleasant to my eyes.


Quality of LED output varies WILDLY. Some are very accurate (and very expensive!).

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