My suspicion is...

Hi Rob,

My suspicion is that they are white lights - so that the fireman can see how much smoke he is making at night on an oil burning steam locomotive. Based on the colour/thickness of the smoke, the fireman can then adjust either the amount of oil and/or the amount of air going to the burner in the firebox to get optimum combustion so that enough steam is being made for the locomotive's needs.

Given that most UK locomotives were and are coal fired, it is unlikely that you would have seen this on many locomotives in the UK.

At various times locally during coal strikes some locomotives were converted to oil-burners but most were converted back to coal once the strike was over. The exception was the NSWGR 59 class built by Baldwin/Lima /Hamilton in the US, based on the USRA light mikado design but with a shortened tender to enable these locomotives to fit on a 60' turntable. These were ordered and delivered as oil-burners in the early 1950's, Most  were converted to burn coal, but a few retained their oil-burners until the end and they had that light in front of the stack throughout their working career. Even on some of the coal burning conversions, the bracket to support the light was left in position.  

I'd await confirmation from some of the US locomotive intelligentsia on here, The sun should just about be starting to come up in their part of the world, 

Based on the position

Based on the position it was my thought as well that they were lights to view the smoke color at night.

Stack Light

Yep, what John says.

Anti-pollution 1930s style

Thanks guys.

I would never have guessed what this was, although funnily enough, when I first looked with my 2016 head I had the light hearted thought "pollution sensor". In an indirect way,  that's what it is ......

Another notch in the steam knowledge belt.

Rob Clark

Microphone

I thought it was a microphone ......to get DCC/Sound recordings.

Smoke Light

While these lights were often seen on oil burner, I believe the photo is of two of the Gainesville Midland Railroad's 2-10-0s which were coal burners.

Charlie

I did wonder...

Hi Charlie and all,

I did wonder about the gauze spark traps at the top of both stacks. I couldn't think of a reason for them to be fitted to an oil-burner.

Perhaps on a 2-10- 0 with a power stoker, the coal they were using was more powder than lumps?

You can set the auger speed

You can set the auger speed on a power stoker, which would then be reflected by the color of the smoke.

Smoke Light

I don't think that any of the GM's half a dozen or so locomotives had stokers and there were lots of stoker equipped locomotives that didn't have smoke lights. However the GM did run steam up until 1959 so they may have been under community pressure to keep the smoke down as times changed and communities became less tolerant of pollution sources.

Charlie

...

doh...

No.

You manage steam power operation by monitoring the smoke.  Two dark, too much fuel.  Too white, too much water.  Right in the middle, preferably a nearly clear vapor, perfect.

Smoke Density Light

It's called a smoke density light. These were far more common with oil burners as it's quite easy to have the firing valve open too wide for prevailing conditions. Obviously, the lights were for checking smoke density. during night time operations as smoke is readily observable during daylight.

Someone mentioned the Gainesville Midland. As it turns out, there's some footage of GM 2-10-0 #208 in operation available on YouTube:

Here's a clear pic of a smoke density light ahead of the stack of Cotton Belt #777, an oil burning 2-8-0. http://mononman.rrpicturearchives.net/showPicture.aspx?id=4408882,

Mike

Coal firing efficiency

Some great feedback here - it's a fascinating topic and way more complicated than first appears.
Here's an old UK video about efficient firing on a coal fired locomotive which clearly explains why black smoke occurs as well as a lot of other interesting issues:
Its a great watch (if you are a steam buff ....).

Rob Clark

Brass model with smoke light

Here a brass model of such an loco with smoke light, a Hallmark HO-scale model of 182-187 class of the Frisco.

I think that this a very seldom modeled part on steam loco models.
This could be a good idea to replace the lamp by a 0402 LED.

Yup... smoke density light.

Yup... smoke density light. Learned that nigh 40 years ago when I too, spotted those in photos of Frisco steam engines and wondered what in the world that was.  My long time friend (he's now 84) told me then what they were. He knew (knows) his stuff about steam engines!

Smoke light

Our SP cab forward 4294 at the California State RR Museum has a smoke light behind the stack and to the right side of the smokebox.  I met a family descended from an SP engineer named Chester Black who they said had suggested such lights to the SP, long before 4294 and the other AC-10/11/12s were built, of course.

Steam locomotive equipment question

Yes the light is designed to assist with firing locomotives by highlighting at night the density of the smoke. Oil burners all had them, and predominately at the rear of the funnel.

For coal fired locomotives many had them position either at the rear of the funnel and often in the case of NSWGR 57 and 58clas mountain types they were positioned on a bracket just forward of the smokebox/boiler ring. Although the fitting of them did not take place until the early 50's as they went through overhauls in worksops.

The AD60class garratt's had a light to the front of the funnel from the very beginning the first locomotive over here that had them, and was positioned at the top of the smokebox edge.  The earlier 57 & 58cl were all generally supplied with two or three types of coal generally and over type the crew were very well versed in the type of coal and firing method of them, with the steam gauge and water levels being the main indicator and constant looking at the fire.

Later in service the garratt's were supplied with a much wider variation of coal from quite a few different areas and allocated to depots where a mechanical stoker was never seen, these men took a while to get used to them and the night light was more a use to them than for crews at depots that worked on them and the earlier types more frequently.

Every type of coal used was different in its heat and ash content, as a result, some coal would require an almost clean funnel, while others would would require varying levels of smoke densities, the Northern highly volatile type needed smoke as it burnt fast, little ash and care on undulating terrain as ash often would not form deep enough to form a strong ash bed.  As such the lights helped but not in every case.

Yes the light is designed to

Yes the light is designed to assist with firing locomotives by highlighting at night the density of the smoke. Oil burners all had them, and predominately at the rear of the funnel.

For coal fired locomotives many had them position either at the rear of the funnel and often in the case of NSWGR 57 and 58clas mountain types they were positioned on a bracket just forward of the smokebox/boiler ring. Although the fitting of them did not take place until the early 50's as they went through overhauls in worksops.

The AD60class garratt's had a light to the front of the funnel from the very beginning the first locomotive over here that had them, and was positioned at the top of the smokebox edge.  The earlier 57 & 58cl were all generally supplied with two or three types of coal generally and over type the crew were very well versed in the type of coal and firing method of them, with the steam gauge and water levels being the main indicator and constant looking at the fire.

Later in service the garratt's were supplied with a much wider variation of coal from quite a few different areas and allocated to depots where a mechanical stoker was never seen, these men took a while to get used to them and the night light was more a use to them than for crews at depots that worked on them and the earlier types more frequently.

Every type of coal used was

Stack lights

For a little background, the SP Cab-forwards all had "stack lights" ( or "Density Lights", as the SP called 'em) so the Fireman could see how much smoke he was making at night. Bear in mind that the stack was about 60 feet behind him so he couldn't just look up & out the cab window & see the smoke. The lights were on the Engineer's side behind the stack but shone up in the air & essentially thru the smoke. In HO, a 1.5V "grain of rice" bulb is just about the right size for a Stack Light & I've installed them on both of my Cab-Forwards.

Bob Battles