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    Administrator ucfbrett's Avatar
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    Default Lighting question

    If you cross the light beams from two headlamps, does the intersection of them diminish their lumens?

    For example, if you were setting up an enduro car, and you took the inboard headlamps and pointed them significantly outward to illuminate the three-quarter front area, would the "collision" of light with the forward-projecting outboard headlamp cut down overall light?

    Use the headlamp layout of an E30 or E36 or E46 for your mental picture.

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    Aside from lasers, which exhibit coherent waves,it seems that light is not meaningfully affected by waveform interference in the manner that sound is:

    " . . . As I understand the question, this phenomenon has to do with coherence. Light coming from a lightbulb is not coherent because the light waves are caused by the different oscillations of many different atoms. They have slightly different frequencies and wavelengths. So they can only overlap constructively/destructively for short periods. For example, try overlapping the graph of y = sin x with y = sin 1.01x. They only completely interfere for some intervals. The frequency of the light waves is so great that these intervals are very small and infrequent. Also, many light waves can completely add/cancel, while many other in the same place do not, resulting in no noticeable interference pattern."

    https://physics.stackexchange.com/qu...erference-patt
    Last edited by Loose Caboose; 01-03-2018 at 12:01 PM.
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    wooow, this is deep....
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    The lumens would be greater where the beams overlap.
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    Administrator ucfbrett's Avatar
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    Quote Originally Posted by emilio700 View Post
    The lumens would be greater where the beams overlap.
    Yes, that sounds right, but I'm more curious about the effect of the intersection on where the lights are projected. Would they be dimmer? Would both lights still project as far?

    Caboose's post would seem to indicate it should not.

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    Chest hair required Olitho's Avatar
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    Quote Originally Posted by Loose Caboose View Post
    Aside from lasers, which exhibit coherent waves,it seems that light is not meaningfully affected by waveform interference in the manner that sound is:

    " . . . As I understand the question, this phenomenon has to do with coherence. Light coming from a lightbulb is not coherent because the light waves are caused by the different oscillations of many different atoms. They have slightly different frequencies and wavelengths. So they can only overlap constructively/destructively for short periods. For example, try overlapping the graph of y = sin x with y = sin 1.01x. They only completely interfere for some intervals. The frequency of the light waves is so great that these intervals are very small and infrequent. Also, many light waves can completely add/cancel, while many other in the same place do not, resulting in no noticeable interference pattern."

    https://physics.stackexchange.com/qu...erference-patt
    That is a totally illuminating answer.
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    Quote Originally Posted by ucfbrett View Post
    Yes, that sounds right, but I'm more curious about the effect of the intersection on where the lights are projected. Would they be dimmer? Would both lights still project as far?

    Caboose's post would seem to indicate it should not.
    More lumens = more light.

    The beams in no way "cancel" each other
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    Brett, while it is an interesting question with some illuminating (sorry) answers, this kind of approach would be woefully insufficient for night endurance racing. In one of the last WERC enduros at Buttonwillow last year, Ryan was asked to co-drive a Spec e30. The owner had equipped the car with high-wattage lamps in the OEM locations and the car, in my opinion, was still hard if not dangerous to drive at night. Simply not enough light overall as well as poor if any apex lighting. There are some very good and very inexpensive LED lights on Ebay that would quickly surpass virtually any bulbs in the OEM locations.

    Lighting IS very important. For the Exocet we are building for E0 (you will see it at Buttonwillow if not sooner), we went with some massive LED main lights (28 5-watt CREE bulbs per side) and some separate apex LED lights aimed out ~30-degrees. Unlike a street car, by definition a good race driver is very rarely looking in the direction the car is (currently) pointed.

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    Administrator ucfbrett's Avatar
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    I ask because it is part of a lighting recipe, but not all of it. I don't even know what light is (solid? liquid? gas?), which is why I asked.

    I have used my Miata for enduros and even with added light bar and the stock lamps enhanced and angled outward, the end result was little more than meh.


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    Is light a particle or a wave ? This is heavy !!!!
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    Light is pure energy, Physics calls a packet of light a photon.
    Photons don't interact with each other except in rare circumstances, so the brighter your lights the easier it is to see.
    If you beam a million visible photons into a volume of a millionth of a meter on a side, then you get a phenomenon called pair production where the photons turn into electrons and anti-electrons.
    Unless your head lights are as bright as the interior of the sun, you don't have to worry about pair production.

    For night racing: Try for 10 to 20 thousand lumens in a fan 5-10 degrees vertical and 60 degrees horizontal, with more light in the middle down the road.
    Mount the lights as high as you can. Most rules limit to fender height. It's hard to do night testing, but you don't want to get it wrong in a race.
    At 150 mph your traveling at 220 feet/sec and you want to see at least 1.5 to 2 seconds ahead.
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    Quote Originally Posted by bellwilliam View Post
    Is light a particle or a wave ? This is heavy !!!!
    If a visible light photon's energy is converted into it's equivalent mass then the photon would weigh approximately 6 x 10^-37 kg. Light is very light.
    Although a photon has no rest mass.
    Last edited by rikgray; 03-10-2018 at 03:42 PM.

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    I can't tell you about the science part but of all the interviews/scenes I've been a part of lighting, I've never had the addition of a light reduce the overall available light. However, if you make one area of light super bright, the areas of less light might seem darker. I would think having the light as even as possible would be best.

    Think about putting a really hot key light on your subject then when you make the camera work for that key light, your backlight might all but disappear. It's more of a latitude of the camera or your eyes though not the actual available light. Your eyes likely have better latitude than most cameras.
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    Quote Originally Posted by rikgray View Post
    Light is pure energy, Physics calls a packet of light a photon.
    Photons don't interact with each other except in rare circumstances, so the brighter your lights the easier it is to see.
    If you beam a million visible photons into a volume of a millionth of a meter on a side, then you get a phenomenon called pair production where the photons turn into electrons and anti-electrons.
    Unless your head lights are as bright as the interior of the sun, you don't have to worry about pair production.

    For night racing: Try for 10 to 20 thousand lumens in a fan 5-10 degrees vertical and 60 degrees horizontal, with more light in the middle down the road.
    Mount the lights as high as you can. Most rules limit to fender height. It's hard to do night testing, but you don't want to get it wrong in a race.
    At 150 mph your traveling at 220 feet/sec and you want to see at least 1.5 to 2 seconds ahead.

    This is, pun intended, brilliant.

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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by Red_5 View Post
    Think about putting a really hot key light on your subject then when you make the camera work for that key light, your backlight might all but disappear. It's more of a latitude of the camera or your eyes though not the actual available light. Your eyes likely have better latitude than most cameras.
    as if you are a camera guy
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    Quote Originally Posted by ucfbrett View Post
    This is, pun intended, brilliant.
    I didn't understand any of that. I am not too bright.
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    Kinda too dim to get that too....
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    Quote Originally Posted by bellwilliam View Post
    Is light a particle or a wave ? This is heavy !!!!
    Light is particles that propagate as waves - really fast!

    1-thefirstever.jpg
    Last edited by Loose Caboose; 01-05-2018 at 02:17 PM.
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