1. What light sources should I use for color evaluation?

ISO 3664 species that in the imaging industry – graphic arts, photography, and graphic design – 5000K lighting, a.k.a. D5000 or D50 as it is commonly referred to, is the best light source to use. It has equal amounts of Red, Green, and Blue light energy, so it will not accentuate or subdue any colors. In imaging applications, many colors are viewed at the same time (e.g. a photograph), so all colors need to be represented evenly. This is why an equal energy light source is so important to this application.

D5000 should be the primary source, but a secondary source can also be used. In packaging applications, using the source used in the store would be useful. This is typically a high efficiency fluorescent lamp.

Old color evaluation booths also offered 7500K lighting. This light source was only used to help the pressman see the yellow ink on the press sheet. This was dropped from the standard (ISO 3664) over ten years ago. D50 is the only ISO standardized source now used in the imaging industry.

2. Is it necessary to have Ultraviolet (UV) energy in the light source for the imaging industry?

In ISO 3664, a CIE rating is referenced and this rating includes a level of UV to be included in daylight sources. UV is a natural component in natural daylight. To simulate true daylight with a man-made light source, including UV is necessary. However, the imaging industry frequently uses optical whitening agents in substrate materials, e.g., paper. These agents absorb energy in the UV area of the spectrum and re-emit them in the visible region of the spectrum, usually in the blue region. This helps the paper to appear “whiter”. Unfortunately, this effect is not always desirable. When matching a proof to a monitor, the monitor will not exhibit these optical whitening characteristics, so the proof and monitor will never match each other. For this reason, having lamps that emit only small amounts of UV energy is desirable in many applications.

3. Why is simulated daylight using a high quality fluorescent lamp better than simulated daylight using a filtered tungsten source?

Fluorescent daylight technology has made great advances over the past 15 years, and GTI Graphic Technology, Inc. has actually helped this along. The main advantages of a high quality fluorescent daylight source are:

  • They will include UV energy in sufficient amounts for the simulation of daylight (filtered tungsten requires the addition of a separate UV lamp to provide enough UV energy to properly simulate daylight).
  • They do not produce excessive amounts of heat (filtered tungsten produces over 5000 BTU’s of heat).
  • They do not use filters (filters fade or change color requiring periodic replacement);
  • Because they do not use filters, proper intensity at the correct color temperature is easier to achieve with fluorescent daylight.
  • They consume less power.
  • They do not require special cooling or ventilation systems to stabilize the lamp color temperature (filtered tungsten must keep lamps within a tight temperature range or the color output will change).
  • They do not require high amperage circuits (20 AMP or more), which are expensive to install. They will run on a normal 10 AMP circuit.

But not all fluorescent daylight lamps are the same. GTI Graphic Technology is one of the few suppliers of lamps that meet the industry requirements for color viewing applications.

4. Are there special electrical requirements for any of the Graphiclite® booths and luminaires offered by GTI Graphic Technology, Inc.?

No, they can be plugged in to any normal outlet with a rating of at least 10 Amps. However, due to the use of electronic ballasts for the fluorescent lamps, they should never be plugged into a battery back-up system (Uninterrupted Power Supply).

5. Why is the booth the Munsell N8 gray? Why not white or black?

Industry standards specify the surround for evaluation of photographic prints and printed materials should be Munsell N8 gray. A chromatic color (e.g., Red, Green, Blue) will influence and bias the color perception of the viewer. For this reason, an achromatic color (black, white, or gray) surround is needed. Munsell N8 is a medium gray tone, about half way between black and white. Therefore, it works well for almost all color evaluation applications. GTI’s Graphiclite® viewers and light booths for the imaging industries all have a Munsell N8 surround. GTI offers N8 paint in both pints and gallons.

6. Why do colors look differently under different light sources?

Most all samples will appear differently under light sources having different color characteristics. A Blue source will accentuate blue colors and subdue reds and greens. A Red source will accentuate red colors, etc. This is called Inconstance. Two samples can match under different light sources but both still shift in color. Inconstance cannot be eliminated, only reduced using the proper mixture of dyes or pigments. It is very important to know it exists and observe its effect on the color of the sample to see if the inconstancy is overly objectionable. Keep in mind that a determining factor in color is the light source. If the source does not have Red energy, there will be no Red energy for the object to reflect and therefore will not appear Red.

7. Are color viewing booths built to some national or international standard?

Yes. Color evaluation booths, used for imaging applications, should conform to ISO 3664:2009. This standard specifies the surround color of the booth, the light sources to be used, with their minimum color characteristics required, the light levels that are required on the viewing surface, and procedures. The daylight source is D5000, as specified by this standard, and is used for both reflective and transmissive art work.

8. What is CRI?

CRI is the abbreviation for “Color Rendering Index.” It is a method of rating how well colors are rendered by a light source when compared to a standard theoretical source. A CRI of 100 means it will render colors very well. A CRI of 23 means it will not. For color assessment applications, a minimum CRI of 90 is required.

9. What does D50, D65, and D75 mean for daylight sources?

The “D” indicates it is a daylight simulator. The numerical value indicates the color temperature of the lamp (5000K for D50, 6500K for D65, and 7500K for D75).

10. What daylight source should I use, D50, D65, or D75?

In the imaging industries (Photography, Graphic Arts, and Graphic Design) D50 is the standardized source. D65 is used for color matching applications in the inks (but not ink on paper), paints, plastics, and textiles/apparel industries. In the imaging industry, D75 was used to help printers see the yellow ink of a process color print job and it is also the old daylight source for color matching applications. It is still used for some specialty applications (color vision testing for example). Most applications now require the use of either D50 or D65. GTI Graphic Technology, Inc. offers lamps in each of these color temperatures, in an assortment of sizes.

11. f the lamp says it is a D50 lamp (or D65 for that matter) are they the same, even from different manufacturers?

NO! Like all products, lamps are manufactured to meet certain needs. For most commercially available D50 and D65 lamps, the manufacturers are trying to produce long production runs and low manufacturing costs to gain the highest profits. Many do not render colors as well as lamps produced specifically for color matching applications. Additionally, they may not emit enough Ultraviolet energy to accurately simulate natural daylight. Make certain lamps have a high CRI value (92 or better) and a CIE Publication 51 Rating of at least B/C.

However, having a high CRI or Publication 51 rating may not be enough. Light booth manufacturers have their lamps formulated specifically to be part of a viewing system. This includes the reflector, the lamps, the diffuser, etc. Slight changes in the formulation can create a slight color cast that will influence color assessment. When lamps from another vendor, even another viewing booth manufacturer, are used in place of the original equipment lamps, the color viewing booth may no longer meet the ISO, ASTM, or CIE Publication 51 ratings specified by the manufacturer. Always use the lamps specifically recommended for the viewing booth you have.

Not all 5000 Kelvin lamps are the same!

12. Is exposure to the Ultraviolet energy emitted by GTI’s daylight lamps harmful?

No. Scientists have divided Ultraviolet energy into three very distinct regions; UV A, UV B, and UV C. UV A (also known as “Near UV” because of its close proximity to the Visible spectrum) are the wavelengths from 315 to 400 nm. The skin is sensitive to wavelengths below 320 nm. GTI ColorMatcher® and Graphiclite® lamps emit very little energy below 325 nm. UV B and UV C energy are used in medical and biocidal applications.

13. Can people use light boxes from different manufacturers to compare samples and still get good results?

Yes, providing each booth meets the specifications of ISO 3664:2009, have the same surround color (i.e., Munsell N8), and have a CRI of 90 or better.

14. My booth has become stained after using it. How can I clean it?

For color viewing booths from GTI Graphic Technology, Inc., small stains can be cleaned with mild soap and water. A mild solvent can be tried, but test it on a non-critical part of the booth (the underside for instance) to make certain the solvent will not remove any of the paint. For larger or stubborn stains, a new booth component (e.g., viewing surface) can be ordered and the pieces replaced.

15. If I cannot clean my booth sufficiently, do I need to get a new booth?

No. Replacement panels can be ordered to cover the stained area. As another alternative, GTI offers the Munsell N8 paint in quart and gallon containers that can be applied by brush or roller.

16. Can aides be used inside the booth?

Yes. Some industry practices require the use of viewing aides, such as transparency viewers and monitor displays. These should all be the same color as the booth (i.e., Munsell N8), not interfere with the lights by casting shadows on the print to be viewed, and should be easy to remove. GTI offers viewing aides, such as transparency viewers and articulated monitor stands, in a number of sizes to fit its wide variety of viewing booths.

17. The LiteGuard II monitor information does not display correctly, what should I do to correct this?

Do not hit the RESET button! Small voltage spikes or fluctuations can cause microprocessor-controlled devices (such as the LiteGuard II) to exhibit minor display anomalies. This is a common problem for companies that use heavy machinery or equipment that use a great deal of electrical power, or in industrial areas of a city. To correct this, simply unplug the unit from the main power, wait five seconds and then plug it in again. If the problem continues to occur, place a surge protecting power strip between the main power outlet and the light booth. DO NOT use an Uninterruptible Power Supply (UPS) or battery back-up device, as is sometimes used with a computer. These can damage the electronic lamp ballasts used in the light booths. If the problem continues to occur after installing the surge protector, call GTI Graphic Technology, Inc. – your unit may need servicing (888-562-7066 Eastern Time).

18. I want to use different lamps in my light booth than the ones that came with it. Can I do this?

To maintain standardized viewing conditions, only the lamps recommended specifically for the viewing booth should be used. If an application requires the use of another lamp (the customer is using a specific lamp type and specifies the work be viewed under this lamp, for instance) lamps other than those specified can be used, but only with lamps of equal size and wattage ratings. For instance, a T8 lamp should not be used in place of a T12 lamp (the lamp size will be listed on the lamp itself). An example of a lamp code is given below:

19. My Graphiclite® light booth never “turns off”. The LiteGuard II is always on when the rest of the lights are off. Shouldn’t it turn off completely?

No. This indicates that power is being supplied to the unit and it is ready to use. If local safety requirements state that equipment must not have power connected to it when not in use or when the business is closed, insert a surge protecting power strip (not an Uninterruptible Power Supply) between the unit and the main power source.

20. I have power interruptions in my area. Can I use an Uninterrupted Power Supply (UPS), like I use on my computer, with the light booth?

No! This type of power supply is actually a DC battery with a circuit that imitates AC voltage. It will damage the electronic ballasts used for the fluorescent lamps.