What is the best Light Color

payloads

#1

I continue to research external lights and I am pondering the best light “temperature” in Kelvin. At 5500K we have white “daylight” of the noon day sun and at 3000k we have the warm glow of light bulbs or afternoon sun. The later is better for photos of course, but is that what we want?

We know that blue light travels a lot further in water than red light. The best “light” for seeing into the distance seems to be about 500nm. That may go twice as far a yellow light. So is that the light we should use for steering and navigation? Especially when it is really dark like in a mine shaft or a cave?

The catch is that a color temperature in Kelvin is a full spectrum light source, so we have to approximate to find the best light.

Col temp (Kelvin) = 3,000,000 /Wavelength (nanometers)

So 500nm suggest we want a color temperature of 6000k.

My current external lights (below) are in the middle at 4000k, but I just ordered some that are 5700k and some that are 3000k. Has anyone else made a comparison or thought about this? Should we just be using blue LEDs for navigation and then turn on white lights to film?


#2

Hi Chris,
I am a diver and have gone through a ton of lights through the years. In my experience there is no one light that can do everything, as you have concluded with out spending the $$$$ I have. Lights that will give you good penetration in low visibilty create significant over exposure when a video camera hits it. And a good video light doesn’t always penetrate the turbidity. As far as temperature I have had great luck in around 5K. It doesn’t the warmest colours but it does the job well.
I notice that a lot of OpenROV people are working on integrated lights, powered from the onboard batteries. It’s great to build and create, I understand that better than anyone. But if you want the best lights for underwater…go to the companies that develop and build them. I have mounted 2 small handheld dive lights that I can change the light heads on. One style of head is a 6 degree 1000 lumen made to cut through the silt and low visibility. The other heads are wide angle 120 degree 1000 lumen for video. Depending on the environment I can adapter one or both lights for the job. My common configuration is to have the 6 degree pointed in line with the onboard camera for searching and navigation and my video spotlight in line with a GoPro. This gives me the best of both worlds as the GoPros video quality is way better than the onboard camera.

Hope this helps, any questions don’t hesitate to ask.

Cheers,
O


#3

Hello Chris! I am a robotics student and I am using the 2.7 as a research platform. You may be interested to know that I am in the middle of a project pertaining somewhat to your question! While I am sure that the research has been done on various lighting systems for divers (this was the first place I tried to source lights), the problem is that, as far as I can tell, the research is proprietary. Because I can’t cite the guys selling the sticks on how great their sticks are, I have to do my own experiments. My specific research is how best to see through turbid conditions. The stock lighting systems reflect particulates in the water column very well. If your interested in what I have found or have any ideas I would be glad to talk further on the matter, just PM me!


#4

@BlueRoamer - I thought about dive lights, but I could not work out which lights to get or how it would effect the balance and flotation of the ROV. I’m not a diver so the whole field was new to me. There seemed to be a huge choice and range of prices. But I am an engineer, so choosing some LEDs and building a circuit was pretty straight forward. I also like that it is connected to the dashboard and can be toggled and controlled.


#5

Everything you do effects the buoyancy and balance, but a bit of trial and error and a couple pieces of foam takes care of that quick.
I just thought of this if you run into problems. You could use an off the shelf dive light head which would have the reflector and the housing, then attach a cable and run it off the on board batteries and controller.


#6

Hi Chris:

For the lights that are sold by, or are in design by OpenROV, we’ve just tried to scale the color temperature with the anticipated range of the light. The internal ROV lights have a very short range, and we picked a somewhat warm (3500K) color temperature to bring out the red colors when examining things at close range. The external light cubes that are in pre-production right now work well out to a longer range (say, 10-15 feet), and are a more neutral 4000K. Last year we experimented with some spot beams for long-range searching, and those used a much “colder” 5700K LED. The higher color temperatures give better penetration through the water, so this becomes an issue as you start to look out further.

We haven’t really taken water turbidity into account when selecting color temperature. I’m not sure how that would affect things anyway. For turbid water, the best solution is to move the lights as far away from the camera as possible, thus external lights.

-W