2
$\begingroup$

It may be truly a question of life and death.

You know those glow sticks. As a sailor it is a good idea to carry one on our lifevest. Falling into the sea, those glow stick make a light source that helps for rescue.

The idea is to attach a small rope to a glow stick, and make circle in the air above the head. It gives a larger light source ,and it seems also a brighter light source. Making it easier to be located. That was the observation in test, at sea, in the dark. Could it be, or is it just a impression?

In terms of physics, in my opnions, that could be. It is ablut the speed of light, the speed of the circle, and the speed to which our eyes take the light source in consideration. The speed of light produced by the glow sticks is faster than the speed of the glow stick turning in the air. Let say. The rope is 50 cm long, bringing 1 m diameter circle, at the speed of 3 tours per seconds. For the eyes of the search team, the circle created by the glow sticks is not 1 point of light steady, but numerus point of light : the search team doesn t not see a point but a circle. To laso the glow stick at the end of the rope in the air create a bigger source of ligth compares to a steady point. Easier to see.

Bit ot seems also that this circle is brighter that the glow itself: as for our observers, the rescue team, the same light source is adding a light source at the same point 3 times per secondes, adding light to the same point. This is 3 light sources after anothers, but for pur eyes, it looks like 1 brighter light source. Is it correct ?

It should not be correct as a light source is a light source, in circle or not. but by observation (no mesurement) it seems that the glow stick is somehow brighter, into our eyes, (that are no measurment tools), but we get into our receptions nerves, many times per seconds, the same light source, adding to anothers.

Conclusions: for someone falling into the sea, is it a good idea to carry a glow stick artached to a small rope: the source created is larger when turn into the air on itsself, and brighter, which helps localisation.

This is the observation done in the sea: what does physic says about it?

If physic prove it right, than it would be easier for sailor to accept the concept, and theirfor sailor may carry a glow stick attached to a small rope, and this idea may save life.

On the other hand, if this is true, then a turning star would be brighter to our obeservation. But There are big differences between a telescope measurement and our eyes, also between the distance of a star turning or not and a rescue team at sea.

Improve this question
$\endgroup$

2 Answers 2

Reset to default
0
$\begingroup$

No. Say you have a glow stick of $8~\text{lumens}$ in brightness (at least in the start of it's operation), so it produces about $\large \frac {8~\text{lm}}{4\pi~\text{sr}}\approx 0.64~\text{cd}~ \text{(candelas)}$ of luminosity per full spherical angle (in a whole sphere which surrounds your glow stick). So you will get same $0.64~cd$ brightness output, no matter how you move or oscillate a glow stick.

However, if light is very weak (as in a glow stick case) and especially when weather conditions are bad,- like fog, rain, etc,- it may be hard for humans operating at far distances from the light source to spot it. So swinging low light in a circle may keep better resolution between spatial points which human eye needs to distinguish, and hence spot it.

For this reason I suppose swinging of glow stick in a dark is a good option, especially if you have "standard" sticks operating by Chemiluminescence. These sticks are known to decrease in brightness exponentially when time goes by. So any additional effect which makes low light "more noticeable" is of course very wellcome.

Improve this answer
$\endgroup$
5
  • $\begingroup$ Thanks for your answer. $\endgroup$
    – Pierre magnard
    Commented Apr 30 at 14:05
  • $\begingroup$ It isn't necessary to resolve an illuminated object to see it, though - stars are unresolvable point sources with zero angular diameter, but are not invisible. It's not clear to me exactly how or if widening the source might help, the total amount of light reaching the observer is unchanged. It would be a bit like using a telescope to view and magnify the glow stick - it gets visually larger, but possibly dimmer and with no change in contrast to the background. If an object in the night sky is bright enough, it's visible, we only need the telescope to resolve its details, not notice it. $\endgroup$
    – Nuclear Hoagie
    Commented Apr 30 at 14:36
  • $\begingroup$ Nobody says that it is necessary- do not misinterpret me. I'm just saying that of same brightness wider object is probably easier to spot fast by eyes from far distance than of small angular diameter. Say you have moon and star with same brightness, - which one you will spot faster, given that you don't know where to look it for? And I'm not sure if this is comparable to a telescope operation. $\endgroup$
    – Agnius Vasiliauskas
    Commented Apr 30 at 15:18
  • $\begingroup$ @AgniusVasiliauskas The thing is, in this scenario the stationary and spinning glow sticks do not have the same surface brightness, as the spinning glowstick spreads its luminosity over a larger area. A star of magnitude 8 is easily visible to the eye, but a galaxy of magnitude 8 is not, because it has a much larger angular diameter and much lower surface brightness. We should be comparing a small bright star to a large moon with visually lower surface brightness, not a moon and star that appear equally bright but different sizes. I'm not sure which is more noticeable. $\endgroup$
    – Nuclear Hoagie
    Commented Apr 30 at 15:36
  • $\begingroup$ @NuclearHoagie So, Do you want to say that spinning, main sequence star in binary pair is seen as less bright as it would be as if only single? Can you give references for that? As of brightness comparison - candelas are the same of spinning and stationary glow stick as in both ways light from ambient source propagates in full $4\pi$ steradians angle. Check candela definition. $\endgroup$
    – Agnius Vasiliauskas
    Commented Apr 30 at 16:03
0
$\begingroup$

Any small constant light source doesn't get brighter when you circle it in the air, unless it is a glowing ember which glows stronger when it is fanned by the air. Thus, as you already have said, if this is a proven effect, it should be due to the larger extension of the light source which enhances its visibility at night at sea. The total light stream stays the same, but its source is more distributed laterally.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Thank you for your answer. $\endgroup$
    – Pierre magnard
    Commented Apr 30 at 14:10

Not the answer you're looking for? Browse other questions tagged or ask your own question.