The MBTA platforms at Mansfield, Massachusetts feature modern information displays.
As with many modern signs used by passenger railways these use light emitting diodes (LEDs).
You may have noticed that although LED displays seem clear to the eye, in many instances they do not photograph well and appear in your pictures as random spots rather than full letters and words.
This occurs because many LED systems pulse on and off at a rapid rate. You eye cannot detect this pulsing and so you see a steady light, but when a photograph is made at higher shutter speeds, the exposure may capture an LED during the ‘off’ portion of the pulse sequence.
Since the LEDs may not be synchronized with each other, the result sometimes appears as a random collection of spots (each is an individual LED) or if they are synced the pulse may be coupled with a scanning effect that results wide gaps of LEDs in the ‘off’ portion of the sequence. (Such is the case at Mansfield).
This unfortunate effect is especially pronounced when the message is scrolling laterally.
One effective way to expose images of LED displays is to set your camera to a slower shutter speed. This will allow the shutter to stay open for a full pulse cycle.
I’ve found that shutter settings of 1/60th of a second or less will usually work effectively. (It helps to test this, as display pulse rates vary).
Below is a sequence of images that I made at various shutter speeds to demonstrate the effectiveness of slower shutter speeds in regards to the LED display. In each situation I’ve used an equivalent shutter speed/aperture combinations to allow for uniform exposure between images.
In this instance the MBTA train was stationary as it discharged passengers.
Obviously, using slow shutter speeds with rapidly moving trains will present other problems. No solution is perfect.