Beacon Ray Dome Questions

[Mitch]

Hello everyone. I have a few questions about the domes for the Beacon Ray series (Models 17, 173, 174, 175, 176).

1) From an *overall* durability standpoint, which is considered more robust? The glass is obviously heavier, but glass is glass, and (obviously) is prone to breakage.

2) Is overheating, or heat in general an issue when using either a plastic or glass dome? We are, after all, talking about anywhere from 2 to 4 incandescent lamps basically the size of headlights crammed together in a small, sealed space.. Hence my curiosity.

3) Which was more prevalent on emergency vehicles back in the day?

Thanks!

 

[JohnMarcson]

Glass is more rare and fetches a higher price generally speaking. I don't know of any heat issues from bulbs, but "plastic" domes discolor and degrade from sun. I think it is more of a glass is older and more rare thing. But, I'd take a NOS plastic over a cracked glass, so condition matters. You also have narrow 17 versions vs. wider 176 or 174 etc. I'm not a beacon ray collector but dome condition is important, but all things equal glass more desirable.

 

[stansdds]

Glass domes are harder to find and I think Federal Signal charged more for glass, so the plastic domes are more plentiful. For durability, glass domes retain their color in the presence of sunlight/UV light and do not haze or develop the UV crazing that plastic domes can suffer. Glass domes also will not deform when they get hot. Plastic domes are plenty durable when it comes to normal operating condition heat, but when exposed to high heat, such as being near a significant fire, they can deform.

As for normal operating temperatures, Federal signal used only 30 watt PAR-36 bulbs, which do not generate as much heat as the 60 watt 4464 PAR-36 bulbs used in the TwinSonic. Federal did advertise for 1958 a Model 171 Beacon Ray, which they said produced flashes that were not twice as bright as those of the Model 17, but several times brighter. I do not know of anyone who actually has a Model 171 Beacon Ray, I've never seen one, so I don't know for certain, but my guess is they used the PAR-36 100 watt 4509 bulb, which is what was used for aircraft landing lights. With that much heat generation, I'm also thinking that a plastic dome could suffer damage from normal use.

There are two diameters for the 17/173/174/175/176 Beacon Ray. The Model 17 was introduced with a dome that measured 8-1/8" across the lip of the dome. This size was carried over to the Model 173. With the introduction of the 4-bulb Model 174 in 1958, Federal also introduced a larger diameter dome that measures 8-3/8" across the lip. Federal Signal maintained production of 17 and 173's with the small dome and the 4-bulb Beacon Ray's with the large dome until 1964. Beginning in 1964, some Model 17's and 173's would leave the factory with large domes and by 1968, Federal Signal was making all 17 and 173's with the large dome.

Skirts also matter. A small dome will fit in a skirt designed for the large dome, but it is a very loose fit. A large dome will not fit at all into a small dome skirt, it simply cannot pass through the small opening at the top of the skirt.

That was probably a lot more information than you really wanted.

 

[Mitch]

Glass domes are harder to find and I think Federal Signal charged more for glass, so the plastic domes are more plentiful. For durability, glass domes retain their color in the presence of sunlight/UV light and do not haze or develop the UV crazing that plastic domes can suffer. Glass domes also will not deform when they get hot. Plastic domes are plenty durable when it comes to normal operating condition heat, but when exposed to high heat, such as being near a significant fire, they can deform.

As for normal operating temperatures, Federal signal used only 30 watt PAR-36 bulbs, which do not generate as much heat as the 60 watt 4464 PAR-36 bulbs used in the TwinSonic. Federal did advertise for 1958 a Model 171 Beacon Ray, which they said produced flashes that were not twice as bright as those of the Model 17, but several times brighter. I do not know of anyone who actually has a Model 171 Beacon Ray, I've never seen one, so I don't know for certain, but my guess is they used the PAR-36 100 watt 4509 bulb, which is what was used for aircraft landing lights. With that much heat generation, I'm also thinking that a plastic dome could suffer damage from normal use.

There are two diameters for the 17/173/174/175/176 Beacon Ray. The Model 17 was introduced with a dome that measured 8-1/8" across the lip of the dome. This size was carried over to the Model 173. With the introduction of the 4-bulb Model 174 in 1958, Federal also introduced a larger diameter dome that measures 8-3/8" across the lip. Federal Signal maintained production of 17 and 173's with the small dome and the 4-bulb Beacon Ray's with the large dome until 1964. Beginning in 1964, some Model 17's and 173's would leave the factory with large domes and by 1968, Federal Signal was making all 17 and 173's with the large dome.

Skirts also matter. A small dome will fit in a skirt designed for the large dome, but it is a very loose fit. A large dome will not fit at all into a small dome skirt, it simply cannot pass through the small opening at the top of the skirt.

That was probably a lot more information than you really wanted.

Great reply! Thank you for that. One other thing I'm sort of curious about...when did the lexan domes become a thing, and when did they start becoming the more popular option? This catalog below from 1966 doesn't mention anything about a glass vs lexan option, just the different colors.

As an aside...my guess is the material is basically the same as headlight covers today. And I wonder if Federal had used headlight clear coat on them, that they'd have been much more UV resistant than their reputation would suggest.

https://www.facebook.com/rescuemarketohio/posts/pfbid02fH4bCziKkjABHAfZjYAvmUw6qxoe9nWgdn9EkxKokSjjorBscicurCsGkYfqmoXhl

 

[stansdds]

According to FS's sales literature, the tilted clear beam Model 175 was for those who feared the full intensity flashes of white light from the Model 176 would be too blinding.

Lexan domes were advertised by Whelen as "unbreakable". Not too sure about that considering the cracked and broken domes seen on many of their beacons. Federal Signal did not advertise a Lexan dome, but did, with the introduction of the Model 312 Titan in 1968, advertise it as having a special, polycarbonate dome. FS advertised it as "practically indestructable" and "high heat resistance". The Titan was sold with 60 watt 4464 bulbs. Sounds like a special dome for the Titan until you check the FS Service Parts Index, which indicates the exact same part numbers for the Titan dome and the 174-176 plastic dome. So I'm guessing that the standard plastic dome and the special polycarbonate dome are the same and both can withstand the heat generated by a pair of revolving 60 watt bulbs. Not sure about the heat generated by four 4464 bulbs as FS never sold the 174-176 nor the 184 with 4464 bulbs.

 

[Mitch]

According to FS's sales literature, the tilted clear beam Model 175 was for those who feared the full intensity flashes of white light from the Model 176 would be too blinding.

Lexan domes were advertised by Whelen as "unbreakable". Not too sure about that considering the cracked and broken domes seen on many of their beacons. Federal Signal did not advertise a Lexan dome, but did, with the introduction of the Model 312 Titan in 1969, advertise it as having a special, polycarbonate dome. FS advertised it as "practically indestructable" and "high heat resistance". The Titan was sold with 60 watt 4464 bulbs. Sounds like a special dome for the Titan until you check the FS Service Parts Index, which indicates the exact same part numbers for the Titan dome and the 174-176 plastic dome. So I'm guessing that the standard plastic dome and the special polycarbonate dome are the same and both can withstand the heat generated by a pair of revolving 60 watt bulbs.

Thanks for the info. I would guess that at least the later "plastic" domes were pretty durable. Not sure about the plastics they had in the 60's though...because bakelite was still a thing in those days so who knows when the technology finally came along.

That part about the Model 175 was a surprise to me. Until I read that catalog post yesterday, I had always believed the "myth" about the "hill light" being meant for throwing the beam up over a hill. That never really made sense to me, because beams of light aren't exactly that visible in thin air, but angling the much brighter white light to reduce any potential blinding on drivers effect makes much, much more sense. Of course, Federal eventually proved themselves right that it reduced the light's efficacy too much when the straight-beam 176 started outselling the angled-beam 175.

 

[stansdds]

Polycarbonate was developed in Germany, introduced in 1958. Lexan is a form of polycarbonate and was introduced in 1960. I am not sure what sort of plastic FS might have used before 1958 or if all pre-1958 beacons had glass domes.

 

[dmathieu]

In 1953 Federal advertised their dome as Plexiglass.

 

[stansdds]

There you go, plexiglass before polycarbonate came into being.

 

[Maxim2Eng]

The major difference between glass and plastic is how much candle power is absorbed by the material. Glass allowed almost all the candlepower to pass through whereas plastic absorbed quite a bit, e.g. red absorbed almost 85%! On the other end of the spectrum, amber absorbed 15%.

My VFD had a Chevy Blazer equipped with a model 11 Twin BeaconRay with 4 4509 100w bulbs. It saw years of service and lots of use, and heat was never a problem (and 10g wiring kept the power flowing). Another department I was on had a 61 IH pumper that was a tad too close to a barn fire (my dad used to claim they never lost a foundation) and the plastic dome deformed but only slightly—not enough to replace it.

When I was a kid, the KSP tried to get exclusive use of blue domes, but the courts said no and all police agencies went to blue lights (I’ve slept since then but I believe it was in the early/mid 60s). Jefferson County Police (outside of the city of Louisville) equipped all their cars with 174s with blue glass domes and none were ever damaged under normal service use.

FYI, gold is added to molten glass to get the red color, cobalt for blue.