Yesterday, 13 October 2018, I exposed these views of an LED (light emitting diode) signal on Irish Rail at Limerick Junction.
Take a careful look at the yellow aspects in the respective images.
In the top photo, the yellow LEDs appear relatively dim (and much dimmer than they seemed in person). On the bottom photo these are brighter.
Many LEDs do not produce constant light output and flicker many times a second. Although you cannot see this with your naked eye and the light output appears constant, in fact the light is blinking. When you use a fast shutter speed the camera only captures a portion of the light emitted and so the signal lights seem too dim.
The key when photographing LED signals is to use a relatively low shutter speed. In this case 1/60thof second is much better than 1/400th.
Another tip when making effective LED signal photos is to make the most of subdued lighting which can make the signals seem brighter than the light around them.
On the surface, it looks a like a standard pattern three-position upper-quadrant semaphore blade, commonly used by many American railways beginning about 1908.
The flat-end red blade with white stripe would have been typically used for an absolute signal that display a full stop in its most restrictive position.
There’s one critical difference with this semaphore blade; it’s a mirror of the signals typically used in the USA.
On most American railways, semaphore blades were oriented to the right, while in British practice (which includes Ireland) they are oriented to the left. (New Haven railroad was an exception).
I would guess that this signal is an adaptation of the American pattern for service in Britain or Ireland. But where did come from? And how did this anomalous signal blade find its way to Finglas, which is not even on a railway line.
At the moment, this stands as one of signaling’s great unsolved mysteries.
In 1996, I was living in Waukesha, Wisconsin and working for Pentrex Publishing as the Editor of Pacific RailNews. One evening shortly before sunset, a heavy fog settled in. Twilight is my preferred time to make signaling images because lower light in the sky allows for greater emphasis of signaling aspects. Fog is an added attraction, especially for searchlight signals. This style of signal head was developed by the Hall Switch & Signal Company in the 1920s. The searchlight uses a miniature semaphore in front of a focused beam of light that allows for a very low powered lamp to be sighted at a great distance. This effect is most evident when the focused light beam illuminates water droplets comprising heavy fog.