Green from Blue !

[markgengine]

In danger of veering off group topic, I have a couple of marine oil lamps that should show a green light (for starboard) and I want to convert to new fangled electrickery.
Problem is that the original glasses have a strong blue tint that show a lovely green light from the original yellowish oil (paraffin) flame, but I want to use LEDs for display and to date I have not found a suitable combination of filter / lamp colour to get a green light using the original glass. The glasses are curved and one is a fresnel lens so I don't want to replace those.
Any ideas or experience out there ?

[emeritus]

No practical experience, but according to posts on a boating forum I contribute to, it is not normally possible to replace incandescent bulbs in navigation lights. This is because the glass lenses of navigation lights are designed around the essentially point source, omnidirectional, light emitted by a tungsten bulb that cooperates with the lenses so as to provide a sharp cut-off in the beam angle so that you never see both red and green simultaneously. The radiation pattern of LEDs means that the necessary beam shape and sharp extinction cannot be achieved.

Of course this will not matter if they are for decoration only and not for use on a boat.

[markgengine]

This is for decorative purposes only, but I have, with much experimentation, converted a Francis searchlight to LED with reasonable results, but that is just "white" light.

[GrimJosef]

If you use relatively narrow-spectrum green LEDs then the only photons produced will be green ones. Depending on the LED wavelength you choose your blue glasses will transmit a larger or smaller number of these photons, but the glasses won't change the photons' colours. So what will come through the glasses will be green light. The datasheets for the LEDs should tell you their wavelength.

Cheers,

GJ

[Refugee]

Traffic light LEDs. You can get them from the main big suppliers of components.

[seymour32]

Hi, This may be a bit simplistic but if a paraffin / candle flame colour temperature is around 1850K , then I would have thought a LED bulb with a simular temperature would do the job. Most of the DIY stores don't appear to go below 2200k, so it would be a more specialised supplier, but 1800k lamps are available.

[GrimJosef]

How well an LED bulb works will depend on how smooth its spectrum is and to what extent that spectrum is shaped like the (roughly black-body ?) spectrum from a flame.

I just did a very quick web search and it seems that with the advent of cleverer phosphors the spectra from modern LED bulbs are smoother and more completely 'filled in' than once they were. So a modern LED bulb might be worth a try. However I don't know if size might be an issue. Individual LEDs are small and it should be possible to fit them in where the flame once was. Whether there's room for a bulb I've no idea.

Cheers,

GJ

[Analogue man]

A bit late to the party here but the heritage sector of railways in this country have played with this problem principally so that signals can be lit cheaply rather than with paraffin (as they were originally) or lit by incandescent lamps. If I remember correctly several different solutions were found by different preserved railways.

[kalee20]

As GrimJosef says, you can't change the colour of the photons emitted from an LED, so a single-colour LED can only be dimmed by the blue glass, not changed in its tint.

However, a reasonable spectrum, such as might be emitted by red, green, blue, white LED's all together, might get filtered by the glass to give the same retina stimulation as single-wavelength green - and you'd get the visual appearance you want.

The downside is that it would take quite a bit of experimenting, and you'd never get the point-source effect that you want, with the resulting array.

[60136 Alcazar]

The blue glass in railway lamps was to combine with the yellow light from the paraffin burner to produce the green aspect.
From a railway modelling point of view, yellow LEDs are used to represent the yellow glow of incandescent lamps, and (some) green LEDs can be used to represent gas-lamps.

[kalee20]

Originally Posted by 60136 Alcazar

The blue glass in railway lamps was to combine with the yellow light from the paraffin burner to produce the green aspect.

Yes.

The blue glass can't make the yellow radiation green. But the yellow light consists of a spectrum with a bit of blue, and rising amplitude into the red (and below) frequencies.

I'm guessing that as a filter, the blue glass doesn't have very sharp cutoff characteristics, so that with a broad level spectrum of white light, it passes frequencies higher and lower than blue to a significant extent, albeit attenuated.

So when hit by a spectrum which is relatively blue-deficient, green-plentiful, and yellow and red bountiful, the red gets massively attenuated, yellow somewhat attenuated, green a bit attenuated, and there isn't any blue (which would not be attenuated). The output consists mostly then of green.

You therefore need to hit it with a decent green/yellow combination - a cluster of green and yellow LEDs close together might give the result you're looking for.

[SiriusHardware]

You can get RGB LEDs (unsurprisingly containing a Red, Green and Blue LED) and if you made up an array of those you could, using an experimenter's microprocessor board, (Arduino, Pi Pico, etc) pulse-width-modulate the supply to the red, green and blue LEDs to control their apparent brightness.

However, I think this has already been done for you at the commercial level.

There are some fancy 'smart' controllable domestic RGB LED bulbs which already have the facility to choose the exact amount of R, G, B respectively, typically using a standalone remote control or a smartphone app. Find one of those and you should be able to set the lamp to the exact hue needed to be able to compensate for the tint in the glass.

This kind of thing: I haven't looked at it too closely but there is an image of a smartphone app which appears to let you pick the colour you want by touching a 'palette' in the app.

https://www.screwfix.com/p/calex-smart-b22-a60-rgb-white-led-light-bulb-9-4w-806lm/647PY

[G6Tanuki]

Yes, the Philips 'Hue' LED bulbs allow you to choose the chrominance and luminance of your light, I had a few a while ago that were controlled by a dedicated remote control but the modern ones use an app.

[John M0GLN]

I've just read this advice from the 'Boatlamps' website,

https://boatlamps.co.uk/pages/navigation-lights-led-replacement-bulb-information

"If your boat has individual navigation lights, you will get the best results by using red LED lamps behind red lenses and green LED lamps behind green lenses. Maximum visibility is provided by using cool white lamps behind clear lenses utilised for anchor light, stern and steaming lights.
Do not place cool white LED lamps behind coloured lenses as they do not produce the correct colours for navigation purposes.
Warm white lamps are popular behind bi and tri-colour red and green combined lenses for boats up to 12 metres. For boats up to 20 metres see our Bi & Tri Colour light information page."

John

[emeritus]

While the linked page mentions that their LED bulbs meet to requirements for visibility at a distance, they make no mention of the fact that such extended light sources will affect the sharpness of beam cut-off that I understand is a requirement of navigation regulations.

They do give you a warning to check your local regulations

Please note: This document should not be relied upon as a comprehensive document as unforeseen errors may have been unintentionally included. So called ‘International Regulations’ are not always consistent from country to country. So if you need absolutely precise information please refer to the official COLREGS that apply to your locality as there may be ‘Country Specific’ local requirements that need to be met.


This will be of no consequence to the OP, who wants them for decoration only.

[markgengine]

Thanks for the replies folks.
As always, simple things suddenly get more complicated than anticipated !
I decided to start from scratch and filled the oil lamp up and lit to take pics to show the original only to get a blue-ish light not green ! - I had used odourless lamp oil and not the original paraffin, which does produce the correct colour.
I am waiting for the cooler and darker nights to start again with the paraffin as it is smelly and I'm not using it indoors as we have got soft, in the "good old days" as a kid I remember all the farmhouses stinking of paraffin and coal smoke.
Will report in due time when it is a bit cooler weather.
Incidentally I have found that Tilly lamps do not operate properly with "odourless" lamp oil and need proper paraffin.

[julie_m]

Interesting!

I'm guessing the odourless lamp oil burns at a hotter temperature than conventional paraffin; hence, producing a whiter light, which would contain more of the short wavelengths.

[G6Tanuki]

I suspect that orange end of the spectrum radiance from soot particles in old style paraffin burners would have been significant .

[emeritus]

I had the same experience with my pre-war hurricane lamp: odourless lamp oil does not work, you need proper paraffin, which these days seems to cost more than petrol.

[Cobaltblue]

I have some old "tin lantern" pre 60's traffic signal lenses and its noticeable just how blue the green lens is.

It relies on the fact that the quite yellow 70-100W incandescent lamp light was.

Later 50W halogen lenses are green.

Interestingly when in dim the halogen greens go toward yellowy green. They look quite washed out compared to dimmed LED signals.

I think I would use a few yellow LED's and see how it looks.

I can probably lay my hands on an Amber CLS (central light source ) traffic signal LED module for you to try PM me if you want to give it a go .

Cheers

Mike T