Color measurement systems now offer more features at lower cost.
Foremost among the new options are handheld color instruments that make it possible to gather and analyze data on the plant floor. Technological advancements also apply to the new benchtop spectrophotometers, which are smaller, more accurate, and far less costly than their predecessors. Moreover, advancements in software improve capabilities for statistical analysis of color measurements, color correction, and color formulation.
MORE PRECISION AT LESS COST
Until relatively recently, tristimulus colorimeters were the only affordable alternative to costly spectrophotometers for instrumental color measurement. The advent of portable spectrophotometers in the last few years has blurred the line between color spectrophotometry and colorimetry, and the previously dominant colorimeters are now seriously challenged by these low-cost spectrophotometers.
Today's portable colorimeters cost in the range of $4000-6000, down from $6000-8000 five years ago, handheld spectrophotometers can now be had for as little as $6500-7000, although higher-end instruments run $10,000-12,000. Both types of instruments have self-contained microprocessors to store color standards and compute and store measurement data. Operators can see the calculated L,a,b or Delta E values on an LCD display by selecting the required color-space calculation. Some portable spectrophotometers also can display an actual spectral curve.
These portable instruments are best suited to quick pass/fail color evaluation, explains product manager Russ Steimle of X-Rite, Inc. in Grandville, Mich. "Access to a computer via RS232 is necessary to transfer data from the instrument to a database or to color-control software. Then, data can be plotted and evaluated by looking for process trends or compliance with tolerance specifications." Cost of portable spectrophotometer systems when a PC and q-c software are included can or around $23,000 when color-formulation software is added.
Tristimulus colorimeters characterize color by means of three filters to quantify light in each of three broad color bands--red, green, and blue. Spectrophotometers, on the other hand, typically generate 16 to 31 discrete measurements by dividing the visible spectrum--400-700 nanometers (nm)--into narrow bands of 10-20 nm, thus providing more precise color discrimination.
X-Rite sells both types of instruments, but Steimle says spectrophotometers generally give greater accuracy, repeatability, and inter-instrument agreement (measurements by one instrument versus another). The latter is generally in the range of 0.10-0.50 Delta E units for spectrophotometers, vs. 0.50-1.0 Delta E for colorimeters.
Generalizations aside, cost-effectiveness depends on the application, he notes. According to Steimle, the narrow-band discrimination of spectrophotometers is more valuable for brighter colors because the brighter the color, the sharper the peak of its spectral distribution curve. Dull colors, on the other hand, have more of a gentle light-reflectance curve. Consequently, he says a processor doing simple q-c on dull colors (e.g., beige computer housings), could opt for a colorimeter instead of a more sophisticated and costlier spectrophotometer.
While colorimeters are easy to use and calculate results in different "color spaces," they typically cannot predict metamerism, says Elaine Becker, product manager for Minolta Corp.'s Instrument Systems Div. in Ramsey, N.J. "As soon as you get into color formulation and/or color correction, you're better off with a spectrophotometer, which can calculate the match under a variety of illuminants, including daylight, tungsten, fluorescent, etc. Generally, the colorimeter can only be set up with one illuminant at a time, usually C or D65." That limitation of colorimeters has just been eliminated by a new portable entry from Byk-Gardner, discussed below.
Steimle agrees: "For color matching (e.g., recipe predictions) the spectrophotometer is the instrument of choice. Portables allow you to do color-matching predictions on remote samples by downloading the data into a PC that contains the color-formulation software."
TRENDS, IN BENCHTOP UNITS
Benchtop spectrophotometers have also become more affordable. Top-of-the-line, high-performance units now go for $15,000-20,000, compared with $25,000-40,000 five years ago (instrument only). On the other hand, q-c grade benchtop spectrophotometers, particularly those recently brought to market by several suppliers, are selling at or below $10,000. These units offer more features than previous generations and are sometimes packaged with a PC and software.
For example, Macbeth Div. of Kollmorgen Corp., Newburgh, N.Y., is offering a new package of its Color-Eye 2145 compact benchtop q-c spectrophotometer, which features pulsed-xenon light source and 45/0 |degrees~ optics, together with its Optiview q-c software at under $8500. The company sells its ColorChecker 545 portable spectrophotometer with the same q-c software at under $8000. Says product manager Mike Beering, "In addition to our high-performance benchtop instruments, we offer two others--a benchtop and a portable--that are similar in price and whose readings agree with each other, allowing for greater system flexibility."
"The portables have undoubtedly forced the price of benchtops down, and have proven that they can replace them in terms of performance," says X-Rite's Steimle. Bob Van Arsdell, product manager at Datacolor International in Lawrenceville, N.J., also concedes that the most recent generation of portables equals the performance of q-c grade benchtop spectrophotometers. However, he cautions that some users still may need the high-performance class of benchtop spectrophotometers and shouldn't try to skimp on cost. These units give very accurate reflectance curves as well as transmission measurements (the latter not available on most portables). A good example is compounders of automotive materials, who must often work with very dark colors, explains Van Arsdell. "Dark blues, reds, and maroons, as well as slightly-colored grays, can be very difficult to formulate. They demand a spectrophotometer that has high performance at very low levels of reflectance. There isn't much light to measure, so the electro-optical system is stretched to the limits of performance. Also, the parts are usually textured, so the instrument has to be insensitive to stray light. The design of the sphere ports in such an instrument is critical." Other processors that may need these higher-end systems include those compounding materials for appliances or office furniture.
But X-Rite's Steimle asserts, "There are some portable units on the market that are equal in performance to even the high-performance benchtops, except that they don't provide transmission measurements." As noted below, even transmission measurements are now accessible to some portables.
TRANSMISSION: A SPECIAL CASE
When it comes to clear tinted plastics, benchtop spectrophotometers still surpass less expensive portables, agrees William Kober, sales and marketing manager for Color and Appearance Technology (C.A.T.) Inc., a relatively new supplier in Princeton, N.J. "Portable units do reflectance measurements, but very few do transmission measurements through clear plastics such as film because their optics are so miniaturized. Also, the area of view on portables is smaller than on the benchtop models," he says, explaining that the color reading is the average of a smaller area of the part.
Minolta's Becker concurs: "In the past, sheet and film manufacturers have had no choice but to use the high-end benchtop spectrophotometers to measure the color of their transparent products. Portable units, designed for reflectance only, could not give transmission readings." However, Becker reveals that Minolta will introduce in early spring a new portable transmittance adapter that is designed to allow handheld transmission and reflectance readings as accurate as those from a high-performance benchtop spectrophotometer. "This will give the blown and cast film market all the benefits of a benchtop spectrometer, with the added advantage of portability," Becker says. When Minolta's CM-508 portable is purchased with the new transmission adapter, the cost will approach $12,000-14,000, but will still be lower than a high-performance benchtop unit.
THE LATEST IN PORTABLES
All major suppliers today offer portable instruments. Datacolor has come out with a less expensive companion to its top-end handheld spectrophotometer, the Microflash 200d. When the 200d came out in 1992 it was the first portable to feature palm-fitting probes, making it easier to measure any type of sample, whether flat, curved, hard, or soft. "Sample positioning is everything in q-c work--if you can't get a good reading, the instrument is worthless," says Van Arsdell. The Microflash was specially designed to make it easy to position plastic parts--from knobs to panels to armrests. A key advantage is the probe's sample-preview feature that lets the customer see the part almost up to the instant of measurement. The two-part split unit (0.8-lb probe and 3.9-lb base) sells for about $9900.
Newer and lower in cost is Datacolor's Microflash 100d. It also has q-c software but fewer features and no graphic display of color curves; it's priced at about $8500. Interchangeable probes in aperture sizes of 2 1/2, 6 and 18 mils allow measurement of different sample areas.
Minolta offers its new 2.4-lb portable CM-508d spectrophotometer, one of the lightest on the market, with d/8 geometry that conforms to ISO and DIN standards. A key advantage is that additional customized software programs can be created for the CM-508d's optional RAM card, such as one making the unit switchable between inclusion and exclusion of the specular component of reflectance. That feature (also available on Datacolor's Microflash 200d) allows the user to evaluate the effects of a variety of finishes and lighting angles on a color. Minolta's CM-508d, like some other portables on the market, features state-of-the-art, pulsed-xenon-lamp illumination. The latter eliminates the problem of sample heating experienced with halogen lamps and most closely matches the daylight uv spectrum. Light measurements are made in 20-nm wavelength intervals. The unit is priced at $8500.
Late last year, X-Rite introduced the SP88, a high-end portable spheregeometry spectrophotometer with inter-instrument agreement of 0.10 Delta E. It measures at 10-nm intervals, correlating well to most benchtop analytical-type units, and provides specular-included and -excluded measurement readings simultaneously. It can store up to 200 color standards and 999 samples, and is said to be ideal for setting up corporate color-control programs between customers and their material suppliers. It sells for about $12,000.
Color and Appearance Technology's new Spectro/plus portable spectrophotometer has both color and gloss detectors. This dual-purpose system offers a lightweight, handheld spectrophotometer and glossmeter with comprehensive software functions. It has 0 |degrees~ illumination and circumferential 45 |degrees~ viewing, allowing both color and gloss measurement simultaneously on a large monochromatic LCD. Built-in software capabilities include all colorimetric calculations with yellowness, whiteness, brightness, and density indices. In addition, users can customize the unit to their particular operations. It sells for $6500.
Byk-Gardner, Inc., Silver Spring, Md., has come out with an inexpensive, portable instrument said to be the first colorimeter that indicates metamerism. The Handy-Color unit can measure metamerism by means of its multiple built-in lighting sources (daylight C, D65, tungsten A, cool-white fluorescent F2, and narrow-band white fluorescent F11). It has a reflectance measurement range of 390-710 nm, and boasts an accuracy previously not found in portable colorimeters, with inter-instrument agreement of .15 Delta E. Another key feature of this unit is its ability to give readings in plain English by indicating if the sample is "lighter," "more blue," or "more green" than the standard. The 2.2-lb unit, offers both large (0.79-in.) and small (0.43-in.) viewing-area options to accommodate a wide range of sample sizes and shapes, storage capacity for up to 500 samples and 50 color standards, and a variety of display options, including pass/fail, CIELab Plot, and Lab(h) color scales. Handy-Color is priced at about $6000.
In March, Byk-Gardner also launched a new handheld reflectometer, called Micro-Light. Using 45 |degrees~ illumination and 0 |degrees~ viewing, it measures the lightness and or darkness of colored plastics, which can be greatly affected by heat during processing. The 1.1-lb unit is about the size of a small gloss-meter. Unlike earlier versions, it has automatic calibration, can store up to 99 individual measurements, and can give an average of the measurements on a small screen. Data can be downloaded to a PC through an RS232 cable interface for trend or statistical analysis. It's priced at $1950.
Topac Scientific Instruments, Hingham, Mass., a newcomer to plastics markets, offers a new handheld, battery-operated colorimeter from Nippon Denshoku. The NR3000 Color Difference meter makes all standard color measurements with observation conditions based on CIE standard illuminants (options include C and D65 light sources). The unit can measure color differences and can store up to 400 measurements and use the results as reference information. It can convert between different color-space systems, including XYZ; Yxz; L*a*b*; L*C*H; HVC Hunter L,a,b; W; WB; and Y1. Its unique feature is a clip-on printer that connects directly to the NR3000 without a cable. The unit has an RS232 interface for downloading to a computer or external printer and is priced in the $4500-5000 range.
A portable instrument that's said to be neither a true colorimeter nor a true spectrophotometer was launched in December by ColorTec in Lebanon, N.J., a long-time instrument distributor that recently launched its own hardware line. Called a "spectral analyzer" by the company, ColorTec-PCM measures light at 16 points across the visible spectrum, like a spectrophotometer. However, it delivers energy to the sample only at the discrete frequencies being measured instead of across the entire spectrum. Unlike most color instruments, which typically use white tungsten or xenon light sources, this unit combines five different types of light-emitting diodes (LEDs) to cover the entire visible spectrum. Weighing under 1 lb and using a 45/0 |degrees~ degree sensor, it is said to compare in price (under $3000) with lower-end portable or benchtop instruments that use incandescent lamps.
NEW BENCHTOP UNITS
Minolta recently made its entry in the high-performance benchtop market (joining Datacolor, HunterLab, and Macbeth) with the introduction of the model CM-3700d. This spectrophotometer features three measuring diameters (25, 8, and 3 x 5 mm), included or excluded specular component, and continuously variable uv-filter position, rather than the usual two-position filter, offering only full inclusion or exclusion of uv. This reportedly unique feature is said to be useful for measuring optical brightness. Available in d/8 geometry, the unit measures a spectral range of 360-740 nm at 10-nm intervals. Diffuse transmittance and pulsed-xenon lamp are other key features. It is compact enough to sit next to a computer and an RS232C interface allows it to integrate with virtually any system. It is priced around $18,000-19,000. Like all of Minolta's spectrophotometers, the new unit can be used with Spectra-Match software for color matching and the SpectraQC package, which evaluates color and color difference and provides statistical analysis.
Hunter Associates Laboratory, Inc. (HunterLab), Reston, Va., recently launched UltraScan XE, a fully automated, high-performance unit. It automatically performs specular-included/excluded measurement, and permits uv-included/excluded filter positioning for fluorescent quantification. A small-area viewing lens is automatically positioned by the computer for measuring smaller samples. The unit can measure transmittance or reflectance and is versatile enough for q-c, color-strength evaluation, color formulation, and pigment batch rework.
In mid-1993, HunterLab also launched the ColorQuest II benchtop sphere-sensor spectrophotometer, an enhanced version of its original ColorQuest model. Added features include a more versatile and detachable sample clamp, which more easily accommodates samples and sample cells of all sizes and shapes. Also, the new integrating-sphere geometry of the ColorQuest II sensor provides color measurement of transparent, translucent, and opaque samples. Other sensor revisions include more rugged design, specular-excluded/included position control, uv control, and filter position sensing on the front panel (providing confirmation to the operator that the filter is in the uv-included or excluded position). There's also a software interface to a data-storage and analysis terminal--either Hunter's proprietary DP-9000 unit or a PC with Hunter's Specware software for DOS or "Universal" software for Windows.
Colorgen Industrial Group, Inc., Newburyport, Mass., is now marketing a complete benchtop system, which includes its CS-1100 CW spectrophotometer, a 486 PC with SVGA color monitor and printer, and its new QC-2200 q-c software, for $6950.
News in Software
The main news is a slew of Windows versions of PC software for data-storage and analysis. For example, HunterLab recently came out with a new Windows-based "Universal" q-c software program to be used with its MiniScan line of portable spectrophotometers.
And X-Rite launching Plastic-Master, a new Windows-based plastics color-formulation program, which interfaces with both its 0/45 |degrees~ and spherical-geometry spectrophotometers and allows the user to customize data displays with as much information as desired.
Color and Appearance Technology has also introduced Windows-based q-c software. "It has state-of-the-art graphics," says Kober. It can display the measured sample's position relative to color-space tolerances, the latter being shown as either a two-dimensional ellipsoid or a rotating three-dimensional ellipsoid. (Other supplier's systems also display 3-D color space, but Kober says those use spheres rather than the more accurate "true" ellipsoid.) The new software also accepts bar code and is user-configurable. On its own, the software sells for about $4900. It's usually sold together with a color instrument, but it reportedly can work with competitor's products as well.
Colorgen has now come out with new low-cost color-formulation software called Color Formulation Companion System. It is said to include all the benefits of the company's full Color Formulation System but without the database. Companion systems are meant to be used by color vendors' customers and would be outfitted by the color vendor with databases of only each customer's formulations. Besides cutting costs, this protects the security of the customer's and the vendor's databases. The complete Companion System includes simplified Color Formulation Software, Colorgen's CS-1100 CW Spectrophotometer, and a 486 PC with SVGA color monitor and printer. It sells for $11,950.