Message
Re: [colorvision_group] Re: Spyder2PRO Target Color Temperature
2006-11-08 by CDTobie@aol.com
In a message dated 11/8/06 11:02:47 AM, ve2caz@... writes:
Assumptions:
1) Bulb contribution
5000K rated bulbs determine the color temperature of emitted white
light regardless of its intensity.
Right, and if your ambient light is your proofing light a good full spectrum light in the 5000 to 6000k range should be used.
These bulbs are useful in the context of examining prints calibrated
for white at 5000K.
Correct...
2) Illumination contribution
Illumination relates to the intensity and distance of a light source.
Yup, there's an inverse square law involved, but I see people's eyes glaze over as soon as I start on that stuff.
Relative illumination (light intensity in candelas / meter^2) measured
at the monitor represents illumination minus distance loss.
If you refer to the monitor, then luminance in candela's per meter squared is correct. If you are referring to ambient light, that technically is not luminance its illuminance, which has different components and units. But thats way too confusing, and since it never shows in Spyder2PRO, and users just see numbers in Candelas, as they would for their monitor we'll ignore it. Whats most important there is not the numbers, but the 5 categories, and explanation of what those ambient light categories relate to.
I can measure this (in candelas / meter^2) using the provided colorimeter.
Yup...
If the colorimeter is pointed at the monitor, I am measuring the
monitor contribution whereas if it is pointed away from the monitor I
am measuring the contribution of the light source.
Contribution wouldn't be my word. But, yes, you measure the monitor, and you measure the ambient light, and the software suggests settings that will coordinate the two.
Both sources of light contribute to the overall illumination affecting
the eyes.
Correct...
Rods (B&W vision) are more sensitive to low illumination whereas cones
(color vision) require more illumination.
Yes...
To properly assess color one needs enough illumination so that eyes
use mostly cones.
There's a range there, given the weak output of CRTs, where the rods are having an effect, and you need to work with that, by using a lower monitor whitepoint.
With high levels of ambient light one should select higher temperature
monitor targets where as in low levels of ambient light one should
select lower temperature monitor targets.
Correct. There appears to be a cap to this, above medium lighting, and 6500k monitor whitepoint, its not necessarily better to keep raising the whitepoint in higher light.
Questions:
Assuming the colorimeter is pointed away from the monitor how much
illumination is required i.e. what would be a good interval measured
in candelas / meter^2 for vision to mostly use cones?
The moderate category, listed as for general LCD use. Not an option for CRTs or even some LCDs that insist on low luminance.
Given measure X candelas / meter^2 within this interval a monitor
target of 5000K should be used, right?
That would be at the low end, where CRTs live, and where your room in dim to dark.
For some reason I am being very "dense" about this but I am trying to
ensure I properly setup my environment to make the most of my color
vision purchase.
Read the help files on the various related screens of Spyder2PRO, and you'll get more info about this.
C. David Tobie
Product Technology Manager
ColorVision Business Unit
Datacolor Inc.
CDTobie@...
www.colorvision.com