Tag Archives: LED

photography, Tips and Technique

Headlights too Bright? Now What?

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I’d heard complaints about this. You’ll find my solutions are the very end of this blog text.

Pan Am Railway’s 7552, a former CSX General Electric-built DASH8-40C (sometimes simplified as ‘C40-8’), features modern white light-emitting diode (LED) headlights.

The sun went in, so I ‘opened up’ the aperture to f5.6. This exacerbated the effect of LED headlight bleed.

The problem is that these white LEDs viewed head-on are much brighter than ordinary incandescent-bulb headlights. Unnaturally bright headlights may have some advantages; they undoubtedly offer better illumination and can be spotted from greater distance.

However they tend to be mesmerizing, which may have something less than the desired effect from a safety point of view.

I first encountered these headlights about 10 years ago photographing an electric locomotive in Munich, Germany.

With the sun out slightly, I used a smaller aperture and also was nominally  off-axis, two things that help minimize the effects of light bleed.

For photography bright LED headlights pose a couple of problems. They can confuse both auto exposure and auto focusing systems, and as a result may contribute to under exposed and/or out of focus digital photos.

Also, many digital cameras only have a limited ability to handle extreme contrasts, resulting in an unappealing effect that I’ll call ‘light-bleed’, when bright light appears to spill over to adjacent areas of the image. A similar problem is a ghosting effect caused by reflections from external filters or inner elements on some lenses.

So what do you do?

I found that these LEDs are only unacceptably bright when viewed head-on, so by moving off axis, you can greatly reduce the unpleasant visual effects of these bright lights. That’s one solution, anyway.

Here I’m significantly off axis, which virtually eliminates the bleed problems.

Another way to suppress headlight bleed is to select a smaller aperture (larger f-number). I work my cameras manually, so this is easy enough to accomplish. If you are using automatic modes, you’ll need to select an aperture priority setting that allows you to control the aperture. Just mind your shutter speed or you might suffer from motion blur.

Tracking the Light Posts Every Day!

 

 

photography, Tips and Technique

MBTA at Mansfield; Photographing LED displays—five images.

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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.

Exposed at 1/250th of a second. Notice the black line as the result of high frequency on-off pulse combined with a scan effect.
Exposed at 1/250th of a second. Notice the black line as the result of high frequency on-off pulse combined with a scan effect.
At 1/125th of a second the effect is less pronounced but still annoying.
At 1/125th of a second the effect is less pronounced but still annoying. Please note that the bottom part of the message is scrolling from left to right.
1/60th of a second works well instance.
1/60th of a second works well in this instance.
This final view was exposed at 1/30th of a second.
This final view was exposed at 1/30th of a second during an interval when the scrolling bottom line of the message was not displayed.

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.

Tracking the Light posts daily.