Time Varying Lights - OPOD

Time Varying Lights - Exploring the Fascinating World of Fluctuating Illumination

Have you ever noticed that lights are not always as steady as they appear? In a captivating composite of images from his book "A Field Guide To Time-Varying Light Sources," author Dan Bennett delves into the realm of time-varying lights, shedding light on the intriguing nature of human and natural fluctuating illuminations. Through this comprehensive guide, Bennett not only provides simple techniques for observing these phenomena with the naked eye but also offers valuable insights on how to capture the peculiarities of time-varying lights through photography.

Twinkling Stars: Unveiling the Magic of Atmospheric Refraction

One mesmerizing aspect of time-varying lights is their ability to create captivating twinkling effects in the night sky. By employing a camera with 1.6-second exposures, Bennett was able to capture the twinkling of celestial bodies such as Sirius, Venus, and Arcturus. Interestingly, the twinkling effect varied depending on the position of the star. Arcturus, closer to the horizon, exhibited more pronounced variations, while Venus, being a disk rather than a point source, displayed smoother and damped twinkles.

The magical dance of twinkling stars is a result of moving pockets of air with different densities refracting starlight. When these fluctuations are strong, they generate caustic sheets that sweep across our vision or camera lens. The mesmerizing colors that accompany this phenomenon arise from the differential refraction of light based on its wavelength. Shorter wavelength blues refract more strongly than longer wavelength yellows and reds, giving rise to a stunning display of colors in the night sky.

Capturing the Dynamic Beauty of Neon Tubes

Neon signs have long been an iconic feature of urban landscapes, but have you ever wondered about the intricate time variation hidden within their glowing lines? By zooming and rotating the camera during the exposure, Bennett was able to reveal the complex nature of neon tube lights. Each stripe represents a half cycle of the alternating current driving the tube. As the discharge travels through the neon gas, it requires a certain voltage to start, resulting in one or more separate sharp lines where the discharge strikes and then dims again. The later, more continuous light creates an enchanting tapestry of complex patterns. The pulses of light that travel along the tube manifest as "grains" and are indicated by the diagonal pattern formed as the camera sweeps perpendicular to the tube. This humble restaurant sign turned out to be a surprising source of richness and intricacy.

Decoding the Enigma of Automobile Tail Lights

Automobile tail lights, often taken for granted, also hold fascinating secrets within their LED clusters. By vertically sweeping the camera during the exposure, Bennett was able to unveil the hidden variations in these lights. One intriguing aspect he discovered was that the LEDs are dimmed for normal tail light display by interrupting their power. However, the outer lights are powered separately because their interruptions are not synchronized with the inner lights. While the reasons behind Audi's choice to have two separate circuits remain unknown, this revelation highlights the intricacies of even the most mundane aspects of our everyday surroundings.

Unveiling the Dynamic World of Las Vegas Slot Machines

In the bustling atmosphere of Las Vegas, even slot machines contribute to the symphony of time-varying lights. Bennett's exploration of these captivating devices revealed their ever-changing illumination patterns. Although specific details about his findings are not provided, one can only imagine the burst of colors and variations that animate these popular gambling machines, adding an extra layer of excitement to the casino floor.

Through "A Field Guide To Time-Varying Light Sources," Dan Bennett has opened our eyes to a world of fluctuating illuminations that often go unnoticed in our daily lives. By embracing the techniques and insights shared in this book, we can develop a newfound appreciation for the enchanting dance of time-varying lights that surround us. Whether it's the twinkling stars in the night sky, the captivating glow of neon signs, the hidden complexities of automobile tail lights, or the dynamic world of Las Vegas slot machines, there is a wealth of beauty and intrigue waiting to be discovered in the ever-changing realm of time-varying lights.

Changing Lights

All is not what it seems in this composite of images from a new book by Dan Bennett (site) “A Field Guide To Time-Varying Light Sources".

It explores human and natural fluctuating lights. It gives simple techniques for seeing with the unaided eye and photographing the oddities of automobile tail lights, restaurant signs and the unexpected behaviour of LED indicators and screens.

The thin lines show – left to right – Sirius, Venus and Arcturus. The camera, on 1.6 second exposures, was jiggled to reveal the twinkling. Arcturus was closer to the horizon and varied most strongly. Venus, a disk rather than point source, has its twinkles smoothed and damped.

Moving pockets of different air density refract the starlight. When strong, the refraction generates caustic sheets that sweep across the eye or camera. The colours arise because shorter wavelength blues refract more strongly than longer wavelengths yellows and reds.

The convoluted reds are a single line of neon tubes above a restaurant. The camera zoomed and rotated during the exposure to expose the intricate time variation. Each stripe is a half cycle of the alternating current driving the tube. The discharge through the neon gas requires a certain voltage to start. The inset shows one or more separate sharp lines where the discharge strikes and then dims again. The later, more continuous, light shows up as quite complex. The 'grains' are pulses travelling along the tube. Their travel is indicated by the diagonal pattern (blur your eyes) made as the camera swept perpendicular to the tube. The pulses change direction with each half cycle. The humble restaurant sign shows surprising richness.

Audi A8 Left and Right Tail Lights

They are LED clusters. The camera was swept vertically during the exposure to reveal the light variations.

The LEDs are dimmed for normal tail light display by interrupting their power. The outer lights are powered separately because their interruptions are not synchronised with the inner lights.

The inset shows the brakes applied. The outer lights are now continuously DC powered while the inner ones are interrupted but on most of the time. Why does Audi have two separate circuits? No doubt there is a good reason.

A busy Las Vegas slot machine

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  • "Time Varying Lights - OPOD". Atmospheric Optics. Accessed on November 30, 2023. https://atoptics.co.uk/blog/time-varying-lights-opod/.

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