The Form 400 was introduced in 1955 as the replacement for the successful Form 109. The Form 400 came with numberous improvements over the Form 109, such as the easy of mantainence. With the 109 you will have to detach the globe from the upper head and reach inside to relamp. With the Form 400 you just open the glass/ring and reach inside to relamp, from the bottom. Also, the tilted refractor and inner reflector are designed for good light distribution. The Form 400 remained in production until around 1960, when GE introduced a ballastless version of the M-400 cobrahead for remote ballasted applications. This particular Form 400 actually has a 250 watt lamp inside, they can be used for either 250 watt or 400 watt operation. This Form 400 is also on the I-Street Bridge, with all the OV-10s, see pics of these elsewhere on this website.
