Various turbidimeters are described that can detect light directly in a substantially circular, e.g., encompassing, manner such that an increased amount of scattered light from a sample vial may be detected by a light detector, e.g., a photodiode or photodiode array. In an embodiment, a substantially circular photodiode array is provided to directly detect scattered light in an arc about the sample vial. In other embodiments, light guides are provided in an arc element that guides light to a detector or detectors. Other aspects are described and claimed.