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Ultra violet use at a night sky viewing event.

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#1 codger81

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Posted 08 March 2013 - 12:33 PM

Re: sciplus.com item #93507P1 mini-uv flashlight $10.95.
I am using fluorescent paint to illuminate a compass rose (N,S,E,W,plus every ten degree point on my three foot dob base for the purpose of alignment. In your opinion, would such a lamp (see above), properly shielded, used to activate the painted symbols be normally acceptable at an event?

#2 FirstSight

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Posted 08 March 2013 - 02:40 PM

If it's truly "ultra-violet" light, then it wouldn't be any bother to visual observers, because it wouldn't be visible to them, but then again neither would it to you. If OTOH you instead mean "deep-violet" but within the visible light-spectrum, then it might be a problem, even shielded, if the indirect glow reflected off your base.

Why not instead use red fourescent light for your compass points? Caution: if there's excessive reflection off your base, especially the flourescence is more bright than dim, then even though the direct light is shielded, it might still be a problem for others.

#3 codger81

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Posted 08 March 2013 - 06:17 PM

OOps...I should have been more specific. The UV lamp with suitable lightproof cowling would be slowly passed over and along the circular line of thirty six fluorescent compass figures, energizing each of them to retain for a time a soft green glow that would last for several hours into the night.
Ultra violet light by itself is outside the visible spectrum, however, certain (fluorescing) objects will glow in it's presence. The compass figures that I am using are small, and I believe would not glow strongly enough to hamper anyone's night vision.....The cowling might be viewed as unnecessary except that some might object to the use of an open UV light exposure to their eyes(for whatever reason).

#4 core

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Posted 08 March 2013 - 09:28 PM

Probably someone with a little more medical knowledge should chime in, but iirc from years back, Rhodopsin/"Visual Purple" in our eyes that is needed for low-light monochromatic vision can be 'bleached out' or lowered production by UV light - one reason a visual observer is suppose to avoid daytime sunlight for x number of hours before observation.

#5 codger81

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Posted 08 March 2013 - 11:58 PM

Thanks to both Firstlight and Core. I can see that use of a UV lamp under any circumstances might become a sensitive issue amongst participating fellow observers.

#6 core

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Posted 09 March 2013 - 03:55 AM

codger81,

for what it's worth, I don't think the amount of UV that the lamp you will be using should be a problem for dark adaptation of fellow observers, it's not like you're shining it into people's faces all the time :D Whether or not it'll affect your own dark adaptation is frankly up in the air, until someone chimes in with more info on the subject - google "Rhodopsin bleached by UV", looks like there's a bunch of studies made (but mostly long-term effect on vision).

Oh, here's a CN discussion about rhodopsin

#7 Tony Flanders

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Posted 10 March 2013 - 05:02 AM

Re: sciplus.com item #93507P1 mini-uv flashlight $10.95.
I am using fluorescent paint to illuminate a compass rose (N,S,E,W,plus every ten degree point on my three foot dob base for the purpose of alignment. In your opinion, would such a lamp (see above), properly shielded, used to activate the painted symbols be normally acceptable at an event?


The UV lamp wouldn't be a problem. But the phosphorescent paint most certainly would be; it's the worst possible color, and probably much too bright as well.

Much better to illuminate the setting circles with your red flashlight.

#8 codger81

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Posted 19 March 2013 - 12:07 PM

Having applied from four to six coats of phosphorescent paint to the compass points, thus strengthening the residual glow effect, I find that the initial use of a UV lamp is unnecessary. The result is a soft but consistent glow lasting throughout the night that should not bother any of the other viewers.
The paint, from www.kosmickreations.net, is water based, non toxic, available in several colors, relatively inexpensive, and easy to work with.

#9 Tony Flanders

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Posted 19 March 2013 - 01:49 PM

Having applied from four to six coats of phosphorescent paint to the compass points, thus strengthening the residual glow effect, I find that the initial use of a UV lamp is unnecessary. The result is a soft but consistent glow lasting throughout the night that should not bother any of the other viewers.


Good luck! I doubt that it's bright enough to seriously disturb anybody's dark adaptation. However, I know a fair number of stargazers who throw temper tantrums in the presence of any light that's not red.

#10 GlennLeDrew

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Posted 11 April 2013 - 04:27 AM

Small splotches of softly glowing green will not bother anyone, unless they're kneeling down right beside them. The light of the sky itself, even at a truly dark site, is -8 magnitude, which is like a fat crescent moon, or 30 Venuses. These little paint bits cannot in any way compete with that.

#11 PitchHitter

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Posted 11 April 2013 - 11:07 PM

I sell the UV lights. Great for finding the nasties that might have crawled in to your tent. They are near Visible LEDs and do produce a light purple secondary color but shielded should be no problem. If in doubt, cover the whole thing with a heavy cloth to charge the phosphor. The light from the phosphorescent (not florescent) paint is insignificant. Been there and done that but as you found out if exposed to sunlight, will glow most of the night. What is this about the sky being -8 Magnitude? If one added all the sources together they might get an equivalent but then that would ignore all the dark space between. Sky Glow under optimum conditions is still darker than about 22 Magnitude. The conclusion is right, the physics is just off.

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#12 Tony Flanders

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Posted 12 April 2013 - 04:43 AM

What is this about the sky being -8 Magnitude? If one added all the sources together they might get an equivalent.


Exactly. Actually, I suspect it's an overestimate, but it's certainly in the right ballbark.

Sky Glow under optimum conditions is still darker than about 22 Magnitude.


That's apples and oranges. Sky glow is magnitude 22 per square arcsecond, but the -8 and 22 are measured in different units, so they are in no way comparable. It's like if I say my car is 20 feet long and you say no, it goes 100 feet per second. The 20 and the 100 are in no way related.

You could also express magnitude 22.0 per square arcsecond as magnitude 4.2 per square degree -- they mean exactly the same thing. And since the hemisphere of the celestial sphere is 20,000 square degrees, that works out to magnitude -6.6 per hemisphere -- not bad agreement with Glenn's figure.

The fact remains that the surface brightness of those phosphorescent strips is a good deal higher than the surface brightness of the sky -- else you could just use a mirror. Come to think of it, that might just work!

#13 GlennLeDrew

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Posted 14 April 2013 - 06:28 PM

Tony,
You've addressed the issue of the sky's integrated brightness nicely. I used -8 for two reasons.

1) The sky brightens toward the horizon (until to within a few degrees, where it tends to darken a little due to atmospheric extinction.)

2) In practice, rare is the site where the zenithal surface brightness is a 'perfect' 22 MPSAS. A more typical dark sky site for star parties might have this at about 21.3, or 0.7 magnitude brighter. And if we naively used this for the whole sky, the integrated light would then be -7.3.

Adding in the milky way and the odd light dome from a populated center, it's not unreasonable to use what might seem to be a pessimistic -8m for the sky glow.

Initially, these glowing paints and such are certainly much brighter than sky glow. But even so, a patch of about 1 square centimetre subtends a pretty small angle from some meters distant, where the light from each might equal that of a magnitude 1 star.

As the evening wears on and darkness settles in, they initially fade fairly quickly, diminishing asymptotically. During 'recharging', one need only illuminate them sufficiently to maintain a readable brightness, not to the point of becoming a veritable landing light strip! :grin:


All,
It bears stressing that the light from "the dark spaces between" is what contributes the most to sky glow. All the resolved stars together add to about -4.4m. If we err on the conservative side and take the sky glow as -6.6m, that's 2.2 magnitudes, or 7.6X brighter than the stars. If you could switch off all the stars, the light reaching the ground would hardly diminish.

#14 codger81

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Posted 14 April 2013 - 06:35 PM

Relevant to the compass orientation in the field of my dob sub-base, I had also thought to plant a phosphor marked north position stake at some distance before night set in to avoid unforeseen delays........Have not really tried this yet.....What do you think?






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