The short answer? Lower is better!
Ultraviolet, or UV light, can be very damaging to a collection. Thankfully, with the advent of new types of lighting like LED, it is much less of a concern than it used to be. Conserv's sensor can measure UV, but in a way that is focused on detection and reduction, not precise quantification.
Conserv's UV sensor functions as a detector, on a relative scale, starting at zero and going up as the amount of detected UV light increases. What this means is that it doesn't measure mW/Lumen like some handheld instruments such as an Elsec. These sorts of measurements are best taken at a lighting source, or over the surface of an object.
The Conserv SCS-1 UV sensor is most sensitive in the UVA range of 315-400nm, as shown in the chart below:
The output from the sensor correlates to a UV index value, on a scale of 0-15. The scale is linear, so a "5" on the scale represents five times the measured UV intensity of a "1".
Where a continuous monitoring product like Conserv is useful is in detecting unexpected UV in a space that should not have any, and measuring if it is increasing or decreasing. This can be caused by things such as window treatments that are reaching their end of life, seasonal changes in the position of the sun, changes to a space configuration, or other factors.