Colorimetry Research CR-250-RH Spectroradiometer
Reference Spectro with big performance in a small size
The CR-250 is a reference spectroradiometer ($6,990 MSRP) from a new company, Colorimetry Research Inc. The all metal design is rugged and practical. What is likely to surprise most people seeing the instrument for the first time is how small it is. Resembling a telescopic sight, it is only 7 inches long, 1.5 inches in diameter, and weighs less than a pound. The CR-250 is almost identical in appearance to the CR-100, the company's very nice professional colorimeter, which is pictured above. The only visible difference is that the CR-250 is slightly longer.
The FOV is quite narrow. For example, when placed one meter from the target the spot size is only 1.8 inches (46 mm) in diameter. Since the instrument has no aiming mechanism this is a useful design choice. Given its small size and narrow FOV, most will find it quite easy to get a good aim point merely by line of sight.
The instrument ships with a nice carrying case with a usb cable and the company's own in-house software. Most will probably opt for custom software, such as ChromaPure which now provides support.
There are two internal operating modes related to refresh rate detection and synchronization. The meter's sync feature can be turned off or entered manually. Unlike the CR-100, no automatic sync detection is provided. Sync is a particularly useful feature and no doubt contributes to the instrument's excellent repeatability, even at very low light levels.
The performance of a reference spectroradiometer is mostly a function of two measurable criteria.
The two other typical standards of performance, color accuracy and repeatability, are assumed as a consequence of the instrument's design. A properly calibrated spectro of 5nm or better optical resolution should provide accuracy to within ±0.0015xy and repeatability to within ±0.0005 within a specified luminance range.
I compared the CR-250 to my in-house reference spectro, a JETI 1211, and the instruments seemed to agree to very close tolerances, so I have no doubts about the CR-250's color accuracy. Its repeatability was even better than the JETIs, especially on certain display types.
Speed and Low-light sensitivity
Traditionally, the biggest drawback to a spectroradiometer has been its relatively low sensitivity. They can be quite slow at low light levels and may not read 10% video at all. Currently, the speed champ among reference spectros is the JETI 1211. Comparing the CR-250 to the JETI instrument is not straightforward, because the CR instrument has four different operating modes:
To complicate matters further, the CR-250 oddly measures at different speeds depending on the display type. [See Manufacturer's Comment] For example, it can require nearly three times longer (given a fixed operating mode) to measure an LED backlit display compared to the time required to measure a refresh display (plasma/CRT), traditional CCFL LCD, or front projector.
With the CR-250 in Fast mode, this is how the speeds compare in seconds.
When measuring LCDs or plasmas, the CR-250 is actually slightly faster than the 1211 at the top end, but at 60% and below the 1211 gains the advantage. Note that in the Fast mode the CR-250 never gets any slower than 7.5 seconds. This highlights another unusual feature of this instrument. The different speed settings of the instrument not only affect the time required to measure light sources, but it also establishes a maximum time for any reading, regardless of its luminance. These are fixed values at
Many spectroradiometers—even those that have different read modes—establish a minimum level of saturation to the sensors before a reading can be successfully taken. The read time depends on how long is required for the required sensor saturation. The Colorimetry Research approach has one drawback here. You can never be certain that the maximum exposure time is sufficient to saturate the sensors to the degree required to get an accurate reading. This is only an issue at the very low end, but it does pose a challenge to those who may wish to use this instrument as a primary working color analyzer that must take measurements throughout the entire video range. It may require switching the read mode at the very low end. As a practical matter, the slow setting will only be needed for projectors.
The bottom line that that this instrument—as I would argue with all spectroradiometers—is best used as a reference against which a tristimulus colorimeter (such as the CR-100) is corrected. Regardless of the attempts of engineers to make a spectroradiometer read faster and measure lower, they are always going to be much slower than a good colorimeter.
So, how does the CR-250's speed compare to the JETI 1211? It is almost impossible to answer that question. If you are measuring an LED, then the answer is "no" (except at 10%). If you are measuring other display types, the answer is sometimes "yes" and sometimes "no". To complicate matters even further, when measuring at 10%, you really need to use the Normal mode for flat panel displays and Slow for projectors. Otherwise, you lose some accuracy. In fact projectors benefit somewhat from the Slow setting even at 20%. Thus, the 7.5 second maximum read time above is not realistic for the entire video range. 15 to 60 seconds is a more realistic figure.
I was quite impressed with the CR-250. It manages to provide reference performance with good speed and low light sensitivity. It does this at a relatively low price. The JETI spectros are the only instruments in the same price range as the CR-250. It's closest competitor, the JETI 1201, has worse repeatability and cannot touch the CR-250's speed or sensitivity. The JETI 1211 also shows excellent repeatability and is, all things considered, somewhat faster in the real world than the CR-250. However, it is also about 20% more expensive.
I do have a few minor quibbles. I have found the virtual Com port driver for both the CR-100 and CR-250 to be a little finicky. I have found myself reinstalling the driver a couple of times and/or rebooting the PC when the instrument would fully respond. These measures have always fixed the problem, but they are an annoyance.
However, when it comes to price/performance ratio of the CR-250 I cannot find any reason for criticism. It is without a doubt the best reference spectro on the market at its price point. It also forms half of a compelling professional combination along with the CR-100 colorimeter. Just a few years ago $6990 for a fast, sensitive reference spectroradiometer would have been considered unthinkable. No longer.