Daniel Reetz, the founder of the DIY Book Scanner community, has recently started making videos of prototyping and shop tips. If you are tinkering with a book scanner (or any other project) in your home shop, these tips will come in handy. https://www.youtube.com/channel/UCn0gq8 ... g_8K1nfInQ

LED lamps 'Warm' or 'Cold' light - Does it matter?

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cday
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LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by cday » 10 May 2021, 13:42

LED lamps are typically specified as producing 'warm' or 'cold' light, the first similar to the light from a traditional incandescent lamp, the latter with a color temperature closer to daylight.

I have read in other threads that cameras normally have settings to allow for light of different color temperatures, I'm not sure whether smartphones which are now an option for use on book scanners can be expected to have similar adjustments?

Are there any other relevant considerations when choosing between using warm or cold lamps?

TS Zarathustra
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by TS Zarathustra » 23 May 2021, 07:09

Cold = sunshine mid-day. Warm = electric lights, inside lighting or sunset.
Cold light gives blue-ish tint to photos. Warm gives red-ish tint to photos.
For reading blue-ish is generally preferred, you get more contrast between the black and white. For people red-ish is preferred. I heard acting coach refer to it as people becoming "prettier" in red-ish light. Blue-ish makes people look pale and sick.
All recent smartphones have built in filters that compensate for "color" of light, and enhance the photo with the correct hue depending on how they interpret the photos contents.

cday
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by cday » 23 May 2021, 07:56

TS Zarathustra wrote:
23 May 2021, 07:09
All recent smartphones have built in filters that compensate for "color" of light, and enhance the photo with the correct hue depending on how they interpret the photos contents.
Do you know how they interpret an image of a book page? ;)

And do modern smartphones have 'auto' and 'custom' options that enable a desired output to be set?

dpc
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by dpc » 24 May 2021, 16:05

I'd strongly encourage anyone that is worried about the color temperature of lights affecting their photographed pages to use a camera that supports custom white balance control instead of a smartphone (although it's possible that some of the camera apps on newer phones may also support this feature).

Besides, if you're just going to photograph books containing dark text on white pages and pump the images through ScanTailor, the color temperature of the light isn't going to make any difference. If you're going to be photographing books containing colored images and are concerned about accurate color reproduction, then I would think that a smartphone isn't what you'd probably be using anyway.

zbgns
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by zbgns » 26 May 2021, 05:14

I would like to suggest rather "neutral" white (4600K) instead of "warm" or "cold" white light source. That is definitely less problematic and gives good results with standard white balance algorithms in smartphone cameras.
I tried also "warm" white LEDs (2700 – 3000K) in the past, but results were poor. Even manual corrections of the white balance (Open camera app) gave only partial improvement. So I would say that it is more efficient to work on the light source (correct temperature of the light) in the first place than fully relying on white balance algorithms.
Last edited by zbgns on 26 May 2021, 06:09, edited 1 time in total.

cday
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by cday » 26 May 2021, 05:40

@zbgns

Thank you for that seemingly very relevant advice!

While standard LED floodlights seem to be almost exclusively advertised as producing either 'warm' or 'cold' light, the output of a LED panel floodlight suggested by dpc can be adjusted continuously between 'warm' and 'cold' colour temperature light... :D

TS Zarathustra
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Re: LED lamps 'Warm' or 'Cold' light - Does it matter?

Post by TS Zarathustra » 30 May 2021, 13:52

cday wrote:
23 May 2021, 07:56
TS Zarathustra wrote:
23 May 2021, 07:09
All recent smartphones have built in filters that compensate for "color" of light, and enhance the photo with the correct hue depending on how they interpret the photos contents.
Do you know how they interpret an image of a book page? ;)

And do modern smartphones have 'auto' and 'custom' options that enable a desired output to be set?
Phone cameras are taking better pictures today than ever before, but they are dumb, also the ones in smartphones. They might take one picture of a page from a book, "think" it's a page from a book, and use corresponding filter. The next page they might "think" it is a slice of cheese and use completely different filter. It depends on software algorithms and other conditions. If you are converting to text the light and filter is not overly important. If you are planning on keeping photos of pages, and not convert to text, it's best to use light that fits the contents of the pages.
I like the Open Camera app. It is powerful and easy to use, with lot of picture options.
https://opencamera.org.uk/

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