bright-field observation
The most basic observation method, bright-field is the uniform wide-field white light illumination of a sample, with either a diascopic (transmitted light) or episcopic (reflected light) detection configuration. Contrast is most dependent on how the samples transmits, absorbs, and reflects light.
Reference
再生医療等製品の製造所における顕微鏡の設置と維持管理に関するガイドライン2017 (JP), modified