Petromax in their manuals and/or advertisements say that the luminosity of the lamps is not controllable. They consider the lamps only on-off. However, if you operate a lamp at a lower pressure the luminosity IS lower. So if you are at the operating pressure for an HK500, that is 2.5 bar, and you release the pressure valve until the pressure and the luminosity drop say to half, what is the problem? Is there any danger with this?
@Antonis Tsolomitis Whether a pressure lantern or a stove, the jet orifice ultimately regulates the maximum output and pressurising the air space above the fuel maintains duration of the firing by creating a reserve of air pressure that ensures the appliance need only be pumped infrequently after that initial effort. Reducing the pressure to ‘simmer’ on a stove that doesn’t have a regulating (controllable) burner is common practice and creates no issues - certainly no ‘danger’ - apart from the burner being more likely to be extinguished by wind if a breeze picks up. There can be carbon deposited on the burner and the jet can require more pricking when output is low. In the case of a lantern, one possible issue is carbon deposition on the mantle (‘black’ mantle) if the output is kept low for any length of time and a need for more frequent pricking of the jet, less likely to remain clean at reduced fuel pressure. Another issue is whether it’s acceptable to have to attend constantly to a lantern on a low setting, pricking the jet often to prevent clogging as I mentioned. Giving a lantern a good ‘head’ of pressure at the outset and only returning to it when it’s evident that it requires more pump strokes to compensate for reducing fuel level (and therefore air pressure) makes more sense. Personally, if I want soft lighting I resort to kerosene wick lamps or a pressure lantern with a shade. John
@Antonis Tsolomitis Operating a well adjusted petronax lantern at 50% luminosity at only 1 bar permanently is feasible. But you should akways start a latern first with regular pressure at 2 bar to fully heat up first. Run 10 mins, then reduce pressure. Some lanterns you can run down to 0,5 bar. But don't leave those unattended. Ps. Larger gap from jet to mixing tube helps fir operating at low pressure. Standard 14mm, i use 16mm.
Sounds to me like you need a 350cp or even 300cp lantern. I've always found 500cp is just too bright to be close to for any length of time i.e. over about 2 seconds...
Actually my lamp is an old (1954, recently restored) 350CP. Being old it did not have a manometer. So in order to learn to use it at proper pressure I bought a manometer. I realized that I had been using it at a much lower pressure than the operating pressure suggested. When I brought it up to 2.5 bars it was indeed too luminous. This is why I asked. I guess I have to use a reflector...or a frosted glass.
What makes looking at the mantle dangerous to the eyes? If I take a led lamp or an incandescent bulb rated at 400 Watts output and try to look at it will I again get an eye burn? I mean is the issue the luminosity level or something else in the spectrum of a lamp with a mantle? Does anyone know what makes this difference? I find my Petromax's light much more warm and pleasurable than a led. So there must be more differences than just the luminosity.
It is easy to find etched or frosted globes that make Petromax style lanterns much easier to look at. I have used them on quite a few of my clones.
In my opinion, there could be a few reasons for you to prefer the light from your Petromax as opposed to that from an LED lamp. The mantle in your Petromax gives off light by being incandescently bright and is more balanced with its different wavelengths of colours. Whereas, the LED source that you happened to look at earlier had probably too much blue in it. That might make it closer to white, which is rather 'harsh' to the eyes. It probably had a reflector within its cell as well and that directed a lot of light energy to your eyes, making it rather focussed and 'concentrated', which could be glaring and painful to look at. But it might not necessarily be the actual luminosity that was causing the discomfort. Luminosity is rather definite in that it has a unit for its magnitude. I think its measured in Watts(W), which is actually the power of the radiating source. Example, if you're looking at a purely red light and compare that with a purely blue light having equal luminosities, which one would be more uncomfortable? Another likely reason could be the mindset. If you're basically a fan of pressure lamps, what else needs explanation? Anyway, you could certainly control the luminosity from the lantern by controlling the pressure and thus the rate at which the fuel is consumed, thus the rate at which its stored chemical energy being converted into light energy. So that amount of energy radiated within that specific amout of time equals to the power. The higher the power of any particular type of light, the more difficult it is to the eyes. This should be compared using light sources having similar wavelengths instead of vastly different ones.
The basic idea of a petromx lantern was to have light where you want it. Often to work. It was not intended to look or stare into. In cold weather it also gives you warmth, whereas led stays cold, ice cold.
OK thanks for your answers. I just wanted to understand if there is different in the physics of light emmited. Of course it was not intended to look at the mantle. I wanted to understand what makes the mantle harsh to look at. From the science side.
That's why, in my opinion, one of the reasons they make different c.p. rated lanterns so you don't scorch your eyeballs!
Obviously not, Wim - I'd imagine the 500cp ones were intended to be raised well above eyeline so that they illuminated a wide area. But then someone comes along at Newark or wherever and plonks one on the table right in front of you...
hhhmm, I doubt this, (besides a lot off other things) ;-) Lanterns are not table based but intended to be carried around, like walking the or a dog. Then the light let you see where to place the feet. The ladies like lanterns, the size of 500cp, size matters here, on the ground to warm up their feet.
Really??.....I've obviously missed a trick here... All the years of fine dining and entertainment along with trips out, gifts etc when all i needed was some sort of lamp-related foot warmer?
If that's the case, Wim, then why is there often a small open loop in the middle of the handle - if not to hang securely off a hook then I don't know what. Absolute piffle Sweeping generalisation followed by a total flight of fancy/fantasy - unless that's what passes for humour in your country...
