Lights for Communication

[gcbryan]

Can someone comment on exactly what light signals are used for communication and the circumstances under which they are needed and well as the requirements of the lights needed to do this?

I saw in another thread that a HID light with a 6 degree spot was unsatisfactory for communications. Is this true even at night?

What signals are commonly used/needed other than back and forth for OOA/emergency/attention and a circular motion for OK/agreement/I see or what ever.

It would seem that a 6 degree spot would work for back and forth emergency signals and a circular motion with that same light at night should be understood as well I would think.

I'm sure it has to do with several divers trying to signal in a cave or something like that but I'm curious.

Thanks.

 

[Diver0001]

I saw in another thread that a HID light with a 6 degree spot was unsatisfactory for communications. Is this true even at night?

The problem with believing things like this is that the person who wrote it probably has one particular application and/or context in mind and possibly isn't aware that not everyone dives in the same way or under the same conditions and/or with the same buddies he has.

Without even reading it, you can be sure that it's true *for him*, but there are no universal truths.

Question the assumptions.

R..

 

[mathauck0814]

I don't know that there are 'hard and fast' rules about underwater light communication. Work this out with your buddy and be sure to know if either of you have light signals that you want the other to recognize. There's no library of "truth" for uw comm. Just best practices.

 

[BabyDuck]

in caves, the three biggies are a circle for 'ok', slow waving for 'attention' (my instructor preferred this to be up & down but said whatever worked), and fast waving for 'assistance now!, otherwise known as 'beating him/her up with your light'.

there are other things you can work out for yourselves, but in cave diving those are the universals.

also needed, though, is enough light for the person in back's light to be seen by the person in front. we do a lot of passive communication where you assume if you can see the other person's light meandering around calmly that they're ok. that's much harder to do with a big discrepancy in brightness between the lights - the light in back has to be bright enough & with a big enough 'hot spot' to punch through the light of the person in front. if the person in front can't see a weaker light, they'll switch places. it's also why the person on a backup goes to the front (or maybe middle in a 3 person team) automatically.

 

[Michael_Lambert]

As BD said above our Okay / Attention / Help.

It also comes down to where you dive, For example someone like me who dives regularly in our great lakes of Ontario where often we can get stuck with Visibility of inches then a higher powered HID with a tight beam is needed to cut through the silt and crap.

One waving a low powered wide beam light would not be effective when it can't cut more than a foot or so through the peasoup. Often we find our selves in situation where all we can see are each others lights and its the only way to communicate day or night.

 

[ucfdiver]

The problem with believing things like this is that the person who wrote it probably has one particular application and/or context in mind and possibly isn't aware that not everyone dives in the same way or under the same conditions and/or with the same buddies he has.

Without even reading it, you can be sure that it's true *for him*, but there are no universal truths.

Question the assumptions.

R..

The thing here is, you want to buy gear that works in most every situation. I have a 21w HID that I can use in a cave to signal, OW during the day to signal, or signal at night. The 21w LED costs about the same as the HID, and in CLEAR cave, it's easy to signal with. The more particulate in the water, the more I want that HID. One of the buddies I dive with a lot has the 21w Salvo LED and I have the Salvo 21w HID, so I'm speaking from seeing the two side by side lots of times in various conditions.

Without a doubt, the best value on the market right now are used Halcyon 18/21w HID's or used Salvo 21w HID's.

 

[TSandM]

As everybody else has said, light signals are pretty simple. The problem with the 6 degree light I have is that the illumination is simply too dispersed, particularly in turbid water. It's difficult to draw someone's attention to a signal, when it doesn't look that much different from the normal random movements of a light when you are simply looking around. When a light is well focused, putting the spot under your buddy's eyes and moving it will instantly gain attention.

Similarly, a dispersed light has little penetrating power, which means it doesn't carry very far, so you have to be quite close together to see the output. If the light is tightly focused, the same amount of light energy carries further.

 

[Peter Guy]

Re the signals and a tale about regional differences. Many of "us" in the PNW use a "flicking motion" of our lights to indicate direction of travel. When friends from SoCal came up, we just did that -- and they complained (or at least one did!) that the signal was very rude, not to mention disconcerting.

Other than the "big 3" I've realized it really does require some topside discussion as to what signals one might be using.

 

[laurin]

Re the signals and a tale about regional differences. Many of "us" in the PNW use a "flicking motion" of our lights to indicate direction of travel. When friends from SoCal came up, we just did that -- and they complained (or at least one did!) that the signal was very rude, not to mention disconcerting.

We do that around here (Finland) too, at least in the groups I dive with. "Flick" is a good word for the movement, fast to the direction of travel and a bit slower back. It's a handy signal when you don't have a clear plan about the direction of travel beforehand - on shallow open water dives mostly, especially when searching a wreck on scooters using a random pattern (my favourite method, you never know what you find that way ) etc.

However, it's a good idea to keep the different light signals to a minimum and making a clear distinction between the slow and controlled attention signal and any more urgent movement, ultimately the emergency. We consciously did this on our last cave course (at Danny's request ), avoiding the direction signals and slowing down our attentions. It does make you a lot quicker to respond to the urgent stuff as any fast movement means that there's something out of ordinary going on.

By the way, none of the above works if the diver isn't in control of the passive light communication - being aware where your light is pointing at and what it's saying at any given moment does take some time to develop...

//LN

 

[HenrikBP]

2 questions, just to have something to compare to:

- is the 6 degrees measured as the full "arc" of the light?

- what is the spread of say a Halcyon 21W HID?

Thanks,

Henrik