separating Nav lights from Street lights; LEDs

[sarabande]

Years ago I found that when using binoculars for picking up navigation lights and buoys, I could differentiate between them and street lights by moving the objective lenses in a small circle.

Lights powered by DC appear as a solid line, and those by AC as a series of dots or dashes.

As I am away from the boat at present, I can't check whether the new generation of LEDs (the arrays used in some marks, not just single ones on boats) can be sorted out in a similar way.

Any views ? ( Sorry ! ;-) )

 

[Anonymous]

That's interesting, I'll try it tonight. I note that Hella Marine's new type approved LED nav lights run from 3V to 33V which almost certainly implies some kind of switching supply. I wonder whether they smooth the dc before feeding the LEDs and what frequency they use. Anyway, a very interesting observation ( /forums/images/graemlins/wink.gif) which could be very useful at times.

 

[chuzzlewit]

I THINK you'll find that LED's look dotty as they respond quickly to alternating current, whereas filament bulbs don't because the filament doesn't have time to cool.

 

[Graham_Wright]

Car rear lights and brake lights in modern vehicles, use pulsed light to vary the apparent brightness. The low frequency they utilise is declared to be very distracting in peripheral vision.
The whole problem could be overcome by increasing the frequency.

Same with nav lights?

 

[Guest]

LED switching power supplies will be high frequency and be smoothed. They will not flash like 50Hz street lights.

The other issues about LEDs are the type of light and how the eye responds. With a broad frequency filament light, the eye/brain can keep the light in the correct position. However with narrow frequency light, the light will move depending on the angle of the eye. Different frequencies are bent by different amounts with our simple eye!. With broad frequency light the brain can interpret where the light is far better.

This is shown on the M25 speed signs when people with glasses that are not looking directly at the red circle and white number see the red circle move relative to the number to the point that the number can be on top of the red line. However, this does not occur for a painted red circle on a fixed speed sign due to the wide frequency spread of the reflected light.

Up to recently there were very few pure light sources. Sodium lights (narrowish) are another type that cause positional issues and are recognised as poor illumination in certain environments.

Narrow frequency light is very poor for good positional estimation and results in the odd surreal effect that LED lighting produces.

 

[Anonymous]

Thanks for explaining that...I have noticed similar effects on teletext and pc screens and always wondered why.