The Seiko Studio Deluxe III L-398A light meter is a portable light meter that uses an AMORPHOUS PHOTOSENSOR (non-crystalline photosensor) as the light measuring element, which can be powered without additional power (no battery). The light meter has a freely rotatable light head, a mechanical stopwatch design, a measurement button lock function, and a memory index function. The light meter can also use incident measurement and reflection measurement. When a specific sensitivity and shutter speed have been selected, the direct reading plate (optional) can be used to directly determine the aperture value.