What is "daylight"?

I looked through the archives, but couldn't seem to find anything

that answered this. Nor are the Kodak/Fuji datasheets useful, they

simply use the term "daylight" as if it's a well-defined term. What

exactly do they mean by this? Is it 5000K, 5200K, or something

else? Is it a specific spectral curve?

 

Is there an ISO definition for "daylight", or can it be anything the

film mfg likes it to be? By that I mean, if I expose color reversal

film under "daylight", at the mfg specified ISO speed, putting an 18%

gray card squarely in the midtones, developing as specified, it will

be rendered a neutral gray at some reasonable midtone density? (I.e.

my ability to control the inputs will determine the accuracy of the

output.)

 

I'm asking this at the LF forum since I get the impression the folks

here are more likely to care, and hence to know the answer...

I believe Kodak uses 5500K as nominal "photographic

daylight".<P>As for your other questions; that will depend on the

color pallete ofthe film you use and the quality ofthe processing,

the accuracy of your shutter and the actual T-stop of your lens

(as opposed to the marked or calculated F-stop) and the

accuracy of your meter.<P>The color transparency film with the

most neutral color pallete currently being made is Kodak EPN.<

P> You have my curiousity piqued: why do you ask?

Ellis is right on. The 5500K designation as "daylight" is an arbitrary convention. Of course, your actual "daylight" will likely differ from the standard depending on time of day, presence of clouds, location on Earth, etc. It may be arbitrary, but at least it gives us all a common starting point, as all film manufacturers follow it, so we can filter as appropriate for the actual "color" of the light.

A Macbeth color chart beats a neutral gray card for judging color temperature shifts and color rendition.

 

Your question about the rendering of the 18% gray card as a middle tone gray is really independent of any color temperture shift in the "daylight" (4800K to 6500K) range. It would just go from having a yellowish tint to color match to having a bluish tint.

 

"Daylight" isn't defined in terms of a color temperature for many reasons (probably many more than listed below):

1) You can't reduce the composit color rendition of 3 color layers into a single color temperature number.

2) The color response of the average human eye has several peaks and valleys so it can't be represented by a single number.

3) Time of day, altitude, polution, humidity, etc. all affect the sun's color temperature.

4) Several widely used daylight films are biased to render some colors better than others: Older discontinued Ektachromes were blue biased, Koadachromes rendered stronger reds, Velvia renders stronger greens.

Jan, I don't know if it's formal or not, but the common terminology in technical photographic writing is like so: sunlight = light striking subject from the general direction of the sun; skylight = light striking subject from sky such that direct sunlight is not also present; daylight = combination of sunlight and skylight.

 

So this means that that for "official" daylight, you must have the sun somewhat behind you such that it is illuminating the subject.

 

I recently posted a response to someone else (non-archived, so it's gone now) about how skylight changes during the day. As I said there, tables exist giving typical spectral breakdowns and correlated color temperatures. I was a little surprised at how steady the skylight was throughout the day. Also, daylight was pretty steady until the sun got fairly low in the sky. Having established a little bit of background, the following quote from some Kodak data sheets (daylight balanced films) pretty much encompases all of the above in one sentence:

 

>> Daylight

 

Use the exposures in the table below for average frontlit subjects from 2 hours after sunrise to 2 hours before sunset. <<

 

Regarding standards related to light sources, the international group specializing in this is called the CIE. You'll probably have to pay money for their literature, however, and unless Kodak specifically says they design for CIE standard such and such, it probably won't matter anyway.

In practical terms, I'd just consider the term "daylight" as a starting point. Every film seems to have it's own "bent" if you will. Some tend to go bluer, some greener, etc. Overall, "daylight" films will be designed to work in the daylight. HOW they will work for you at a particular time, in a particular place is pretty much something that has to be learned from trial and error (or asking on Photo.net). Especially since color can be pretty tricky. Ever have an arguement that goes like this:

 

"Nice orange scarf there, Ted."

"This isn't orange, it's red."

"No, it's orange."

"No, it's red"

Etc.

 

So even if a film is perfectly balanced using the most advanced technology available, you may not even be able to notice because you see the color a particular way!

 

So, in the end, all you can do is shoot some film, and see what comes out or ask around.

A friend of mine who graduated from RIT and interned at Kodak's Research

and Development unit in Rochester described daylight as "the light at noon

on June 21st as measured in Kodak's parking lot."

 

He told me he wasn't kidding and I half believe him. Of course, if this is true,

this would seem to be a great explanation for why I can never seem to match

the film speed on a yellow box of film and need to always filter to get good

color on chrome.

 

I was thinking that maybe Kodak would let me build a studio in their parking

lot so I could get the most use out of their products.

 

Or maybe I could rent the location for important shoots.

 

Cheers.

You have discovered their evil plan! Yes, Kodak will soon be renting space in their parking lot for a very hefty sum of money! It is expected that the value of Kodak Parking Lot Space will soon exceed even the dollar value of the world's most expensive real estate. You think the rent in Tokyo and Manhatten is high....just wait!

I also think he mentioned the asphalt in the parking lot was used to determine

18% gray...