The two most common spectrophotometers are the 0:45 and the sphere (aka diffuse/8°). We get a lot of questions about which is the best choice. Here’s the difference in how these two devices measure color, and guidelines for when to use each.
In a “fixed geometry” or “single angle” device, the first number is the starting point of the light, and the second number is where the light ends up after the reflection off the surface of the sample. In a 0:45 instrument, the light source is fixed at 0-degrees, and the detectors are set at 45-degrees. In a 45:0, the light source is set at 45-degrees and the detectors are set directly overhead at 0-degrees.
A 0:45 is ideal for measuring color on smooth and matte surfaces because it captures the reflection from a sample just as the human eye would see it. While it is feasible to use it to measure shiny or reflective surfaces, it excludes surface appearance and may cause the sample to measure as darker and more saturated than it actually is.
For example, let’s say you have two black samples, one matte and one glossy. Although they are the exact same color black, the data will not match when measured with a 0:45. The glossy sample will appear darker and more saturated, while the matte sample will appear lighter. This is due to the difference in direct reflection (glossy sample) vs. scattered reflection (matte sample).
The interior of a sphere spectrophotometer is actually spherical in shape. By employing a baffling of the light source and reflecting it off of a pristine white matte surface of the sphere’s interior, the detector receives the reflected light at an 8-degree angle from the object’s surface to accurately measure the color.
One of the key points of a sphere device is its ability to measure in either specular included (SPIN, SCI) or specular excluded (SPEX, SCE) conditions. Specular included has the ability to negate the effect of specular reflection off the surface, meaning it only measures the color - not the appearance. Specular excluded includes the surface appearance in the measurement.
As an example, let’s go back to our two black samples, glossy and matte, if you measure both with a sphere using specular included, the resulting measurements should be similar. If you measure them both using specular excluded, the numbers will be farther apart, similar to a 0:45.
Which is best for you?
When it comes to spectrophotometers, one size does not fit all. To truly determine the best instrument for your applications, you must analyze job mix and customer requirements. Get in touch with our experienced Color Experts for help choosing the best solutions for your workflow.