Form 109 Incandescent Streetlight

It was about 1994 when I saw this streetlight, just one of them, in a drive in restaurant parking lot. To be exact it was on a property bordering the tracks on the north side, along the Boston MBTA Blue Line between Wonderland and Revere Beach stations.

I didn't think about it for a few years until 1997 when I went back to see it and it was gone, only the pole minus the bracket arm still stood. In the future I may put "reward" stickers with my phone number on seemingly endangered old streetlights' poles. That is another program.

In the background is a new building under construction. Unfortunately I did not get a picture of the drive-in restaurant, which would have been more historic. The MBTA Blue Line rapid transit tracks are off to the right.

We did not acquire one of these complete. The one pictured here was modeled using parts already in our collection.

Form 109 Close Up

Parts for Form 109 with NEMA head incandescent usage

NEMA head with lamp socket

Socket extender

Adapter ring with NEMA top opening and Form 109 bottom opening (10-3/4" outside diameter).

Incandescent style circular reflector, with opening for lamp neck.

Form 109 globe reflector/refractor

Weight, based on model, about 21 lb. Globe wirh refractor 13-1/2 lb., adapter ring 3 lb., NEMA head 4-1/2 lb. Height with unbranded head as shown, 24-1/2".

The Form 109 with its standard "hood" head was probably the most popular mercury fixture in the 1950's but was also offered as incandescent. On Joe Maurath's web site (, click on Catalogs, then click on General Electric 1950 #1) it includes a cutaway view showing a base-up mounted incandescent lamp. In all my travels I saw just one installation of standard Form 109's as incandescent, probably not more than a dozen fixtures.

Ordinarily a larger head is needed to dissipate the heat from a high wattage incandescent lamp. The catalog page mentioned above states that the Form 109 is suitable for 10000 and 15000 (largest commonly used) watt filament (incandescent) lamps although the incandescent fixture illustrated had the standard Form 109 head. Perhaps the NEMA head was required to be ordered if 15000 lumen (860 watt) lamps were to be used. Another possibility (also conjecture) is that a taller head was needed for longer neck lamps.

In the Boston area the Form 109 globe when equipped with an incandescent lamp seemed to always have a NEMA head. In Boston, I believe the largest installation of these fixtures was Storrow Drive (Soldiers' Field Road), running along the south bank of the Charles River from Harvard Stadium (due south of Harvard Square) east to Leverett Circle (between Lechmere Square in Cambridge and North Station). Another installation was on Nonantum Road from Watertown Square for about a mile east. Both had silver painted Union Metal poles. Nonantum Rd. was attractively tree lined, and some of the streetlights, although only 20 or so feet above the street, were quite hidden by the overhanging tree branches.

The Form 109 was introduced a little before 1950. The first time I recall seeing the lights on Storrow Drive was in the mid 1950's and on Nonantum Rd. in the late 1950's. Thus I would estimate the installations as being of about 1950's vintage. For a long time both of these installations were maintained excellently as evidenced by every one of the fixtures being a Form 109. In the mid 1960's, a few gumball globes started to appear as replacements here and there. I don't recall when the lights were all replaced with cobra heads, that was probably in the early 1970's in response to an "energy crisis" and when I was away at college.

Today most of the original metal poles are still in use on Storrow Drive; they have been replaced with taller concrete poles with truss arms on Nonantum Road.

GE may have promoted the ability to install an incandescent system for less of an initial cost, with mercury conversion at a later date. But converting existing fixtures is not extremely simple, not including the trivial method of installing the ballast and substituting a mercury lamp in the existing socket.

It appears as if incandescent to mercury conversion is better accomplished at the shop rather than in the field. Typical maneuvers needed:

Remove circular reflector for incandescent lamp. (We don't have one of these.)

If incandescent socket interferes with new terminal strip, remove the socket.

Install terminal strip across top of adapter ring. Depending on the dexterity of the technician it may be necessary to dismount the ring from the head.

Connect wires to socket assembly and install arc shaping coil and new circular reflector across bottom of adapter ring.

Mount mercury lamp socket assembly to inside front of adapter ring or inside of globe (depending on mounting provided).

Install ballast (usually in pole base).

Because of the complexity of this procedure it was probably more likely that new GE Form 109 hood heads, pre-assembled and prewired for mercury lamps, were purchased instead if needed. It is still necessary to remove the circular reflector in the field to connect the power leads.

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