Observing the contents in a processing vessel in a hazardous classified location normally requires the use of two sight glasses: one for lighting, the other for viewing. The Series REX-100/NW and SLEX-100/NW eliminates the expense of an additional port and the expense to install it. The explosion-proof UL-844 & SLEX-100 lighting units and the corresponding Series NW sight glass provide glare-free illumination precisely where you want it - at the viewing port.