Darkness Penalties Under Water [Enhanced Senses-related]

Eukie · 10-06-2018, 02:36 PM

The human eye requires light to see, and in water light quickly attenuates with depth. The visible distance light attenuates in water is typically taken to be 74 metres in blue water oceans and a half to a third that in green coastal water. In blue oceans, blue light attenuates at a much slower rate, with visibility distances of about 275 m. The visibility distances used in this measure corresponds to a 98% decrease in brightness, or approximately -3 in GURPS terms.

With this in mind, and some convenient rounding:

Darkness Penalties Underwater
When underwater and the sky is the strongest light source, increase the penalty for Darkness by -1 for every 25 yards you're from the surface in blue water, or -1 for every 10 yards in green water. Apply an additional -1 for every multiple of the respective distance to the target.

In turbid regions with lots of particulate matter in the water, this penalty can easily double, and in brown water it can often go as high as -1 per yard.

Seeing Blue
In blue water blue light can penetrate far. After the first -4 increase in darkness penalties, blue light becomes dominant: instead of the usual penalty, you may increase the penalty by only -1 for each additional 100 yards. If you do this you're only seeing in blue and are colourblind! (p.B127)

In turbid blue water, increase the penalty to -1 for each 50 yards after the first -5 in penalties. In green or brown water blue light doesn't help at all.

Seeing Ultraviolet
Ultraviolet light penetrates deep in clear water, but there's less of it. You can use ultraviolet vision underwater at -1 per 10 yards in blue water, or -1 per 5 yards in turbid blue water. In green water you can use it at -1 per yard at best!

Seeing Infrared
If you have Near Infrared Vision, you can use it in blue water at -1 per yard, -2 in turbid blue water, -3 per yard in green water, and in brown water you're limited to 1 yard of vision.

Thermal Infrared vision and Terahertz vision are almost completely useless underwater: you basically have to touch what you want to look at with your sensor.

Seeing Clearly
A regular human eye is Farsighted (p. B123) underwater because it can't focus clearly when in contact with water. You can ignore this if you wear diving goggles.

10-06-2018, 02:36 PM	#1
Eukie Join Date: Dec 2013	Darkness Penalties Under Water [Enhanced Senses-related] The human eye requires light to see, and in water light quickly attenuates with depth. The visible distance light attenuates in water is typically taken to be 74 metres in blue water oceans and a half to a third that in green coastal water. In blue oceans, blue light attenuates at a much slower rate, with visibility distances of about 275 m. The visibility distances used in this measure corresponds to a 98% decrease in brightness, or approximately -3 in GURPS terms. With this in mind, and some convenient rounding: Darkness Penalties Underwater When underwater and the sky is the strongest light source, increase the penalty for Darkness by -1 for every 25 yards you're from the surface in blue water, or -1 for every 10 yards in green water. Apply an additional -1 for every multiple of the respective distance to the target. In turbid regions with lots of particulate matter in the water, this penalty can easily double, and in brown water it can often go as high as -1 per yard. Seeing Blue In blue water blue light can penetrate far. After the first -4 increase in darkness penalties, blue light becomes dominant: instead of the usual penalty, you may increase the penalty by only -1 for each additional 100 yards. If you do this you're only seeing in blue and are colourblind! (p.B127) In turbid blue water, increase the penalty to -1 for each 50 yards after the first -5 in penalties. In green or brown water blue light doesn't help at all. Seeing Ultraviolet Ultraviolet light penetrates deep in clear water, but there's less of it. You can use ultraviolet vision underwater at -1 per 10 yards in blue water, or -1 per 5 yards in turbid blue water. In green water you can use it at -1 per yard at best! Seeing Infrared If you have Near Infrared Vision, you can use it in blue water at -1 per yard, -2 in turbid blue water, -3 per yard in green water, and in brown water you're limited to 1 yard of vision. Thermal Infrared vision and Terahertz vision are almost completely useless underwater: you basically have to touch what you want to look at with your sensor. Seeing Clearly A regular human eye is Farsighted (p. B123) underwater because it can't focus clearly when in contact with water. You can ignore this if you wear diving goggles. Last edited by Eukie; 10-06-2018 at 04:48 PM.