View Full Version : How Deep Before It's Dark?

14-01-2005, 11:13 AM
One of my young fella's asked me how deep it has to be before it's dark?
Can anyone help me answer this?
I'd guess at about 100 mtrs. ???

14-01-2005, 11:27 AM
hrm, pretty sure its pitch black a lot before 100mtrs.. i would be guessing the bottom of the 24's would be pretty dark ?? ??? Some of the offshore gurus round here will know.

14-01-2005, 11:47 AM
The amount of light penetrating seawater depends upon many factors including the time of day, season, geographic location and the clarity of the water.

When light passes through water, it is absorbed and scattered by water molecules and particles in the water.

As water depth increases, the longer (red) wavelengths are the first to be absorbed and scattered. By about 10m below the surface, most of the red and orange wavelengths of visible light are no longer present (view the pipefish natural light page). A source of artificial light must be used to view reds and oranges. For this reason, many divers carry a torch even during the day.

As depth increases the scattering and absorption of shorter wavelengths (yellows and greens) becomes evident. By about 150m depth, even in the clearest water, human eyes can only see blue light.

Beyond about 800m the human eye can detect no visible light from the surface. At these depths the only visible light is made by living organisms (bioluminescence).

Some deepsea fishes are 15 to 30 times more light-sensitive than human eyes and can detect light in depths down to 1300m

Source - www.amonline.net.au/fishes/faq/deepsea.htm

14-01-2005, 12:19 PM
from my limited exparaince of scuba diving you can see bugger all at 30m without a tourch and thats even in clear midday waters

but what mini typed is very true
amazing to dive on some of the snapper grounds and they look a ghostly whiteish blue
thankfuly crays are a nice dark coulor and easyly seen ;D

14-01-2005, 04:10 PM
As Mini mentions much depends on the conditions, the turbidity, the location relative to land, sediment, time of day, a persons own eyes and all sorts of other things. Things can get pretty dam dark in relatively shallow water.

In clear open ocean conditions under good sunlight conditions well away from land at about 400 feet (120 metres) things start to become strange, by about 800-900 feet (250 metres +) one is really struggling to see black from white and for sure by 1500 feet (450 metres) it's as black as black.


Cheers, Kerry.

14-01-2005, 06:06 PM
BTW, you bleed green at 8 metres. Therefore I don't know how the fish can choose between red and green SPs at this depth. Beats me.

At 3-5 metres visibility at ~30 metres I can sometime still make out the surface. Very hard to get perfect visibility (blue infinity~80 metres visibilty) near to the coast. Best I've seen it was at flinders, but I'm sure at the WRB it would be beaut. My friends have said 80 to 120m vis on reefs off Papua New Guinea.

Snapper grounds with snapper zinging by. Yes racked, stacked and packed all in bluish white. Seen it.


14-01-2005, 06:13 PM
I think Kerry is close to the money . Some of you guys must have dived in some water with very ordinary vis . During my expat days in PNG we bounce dived to 230 feet and you can still see fine except as Kerry says most of the colour is washed out for us mortals at that depth :o :o. As this is a fishing forum the answer is the fish have no worries seeing your bait at much deeper depths than that - lucky for us .


14-01-2005, 07:20 PM
I have dived to 120 ft in fresh water at Mt Gambia it was dark but we could still see OK the water was pretty clear though.

Cats have good night vision maybe we could do some research by sending some of them to the bottom of the ocean? It should be OK as most cats like fish [smiley=angel.gif]

15-01-2005, 01:25 AM
Hagar, ;) PNG :-X bounce diving :-X on what ??? for what ??? in what decade ??? doing what ??? with who? ;D

Cheers, Kerry.

15-01-2005, 07:58 PM
Dug, you're crewl. But are you a CAT?