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My First Light Box. How do I decide?
A few things to consider.
The most popular size light boxes are 12" x 18", 10" x 12" and 18" x 24"
(in that order). Obviously, you need to think about what you want to
use a light box for and how much space you have. If you go with a
larger unit you have the luxury of laying out more than one project at
the same time.
5000 Degrees Kelvin. What does that mean?
Originally the photographic
market didn't have a standard. They looked around and adopted the
standard of the printing industry. Some knowledgeable people said the
standard should have been 5500 degrees Kelvin. That didn't happen.
CRI Rating, Color Rendering Index. What's up with that?
CRI is somewhat subjective, it tells us how clean or pure the light is. It is a system of looking at prints or transparencies, deciding which light gives the best results and assigning it a value from 0 to 100. 100 being the best.
Color Comparison. How to achieve repeatable results?
This is the meaty one.
There are so many things that effect lighting. The color of your shirt,
the ambient lighting, the batch of lamps produced by the lamp
manufacturer, the light box your using. If you read about 5000 degrees
Kelvin and CRI rating above, the idea is to approach northern exposure
midday sun light. A typical rating is CRI 91+, another way to say this
is there is a 9+ error, because it isn't 100.
Lamp Life. Just how long is it?
The way lamps are rated for longevity is the following: Turn the lamp on for three hours, turn it off, turn it on for three hours, turn it off over and over until it fails. When doing color comparison the lamps should be replaced long before failure. A good rule of thumb is based on amount of use. If your using your light box on a daily basis, change the lamps once a year. If your using your light box a couple times a week or less change the lamps every other year. Also burn new lamps in for 10 to 15 minutes before doing color comparison.
Intensity. Is there a standard for intensity?
Yes, it is a broad range
321-497 footlamberts. If the intensity isn't enough you loose detail,
if to bright your transparency appears washed out. Interestingly, as
lamps age, they dim. This has the appearance of the light changing
color, in reality the lamp is still the same color temperature. Bottom
line the most important instrument is your eye. What you perceive
visually is the only thing that matters.
Eye strain. Is there anything I can do to reduce eye strain when using my light box?
Your local art supplies store carries sheets of hard board (frequently used to mat pictures placed in picture frames). Use the hard board when viewing objects of similar size. Cut the hard board to fit the outside edge of your light box. Then cut a window in the hard board to the size of the objects being viewed. This blocks unneeded light from around the object being viewed. What happens is the iris of the eye contracts to cut down on light entering the eye, which can create eye strain. You can make a few different size hard board windows, so you can swap them out when viewing different sized objects.
High Frequency Light Boxes. Why would I want one?
If you plan to use your
light box as part of the lighting, while doing a photo shot, then you
would want to consider a high frequency light box. Conventional
fluorescent systems operate at sixty cycles a second. What this means
is the lamp is turning on and off sixty times a second. When operating
properly the on/off cycle is not visible to the eye, but it is to a
camera. It's when it drops below that speed, we see the flickering
light we associate with fluorescent lamps.