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 Post subject: Chrony and LED lights
PostPosted: Fri Sep 03, 2021 3:28 pm 
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I still have an ancient original green Chrony that dates back to around the 1980s. It works fine in my basement so I have no need to replace. Up until yesterday I had a pair of 60W incandescent bulbs in a ceiling light fixture. I position the Chrony on a camera tripod with it adjusted to 32" from the light fixture. The Chrony works great in this spot and has also worked fine outdoors. Last night I changed the bulbs in that room to a pair of 100W equivalent LEDs. Now I can't get a Chrony reading. Is there any way to use LED lights with a chronograph? Bulbs closer, further, different wattage?

The LED bulbs are rated at 14W with 100W equivalent. After more than an hour of being on, I was able to unscrew them by hand and not get burned. Hardly any heat. I put the old incandescent bulbs in to get some readings and almost cooked my hand removing them only 5 minutes later.


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PostPosted: Fri Sep 03, 2021 3:53 pm 
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You need a spot beam and not flood.......the LED are so bright they are messing with the shadows. I put a shroud around each bulb so the light was only shining straight down. I have since changed to a spot bulb with a narrow beam.

Since the chrony picks up the shadow of the pellet over each sensor, if your lights cast over the other sensor, it will give an error or not register at all.

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PostPosted: Fri Sep 03, 2021 4:15 pm 
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notec wrote:
You need a spot beam and not flood.......the LED are so bright they are messing with the shadows. I put a shroud around each bulb so the light was only shining straight down. I have since changed to a spot bulb with a narrow beam.

Since the chrony picks up the shadow of the pellet over each sensor, if your lights cast over the other sensor, it will give an error or not register at all.



Ahhh... that makes sense. I guess a ceiling fixture in a room with LEDs won't work. Do you use an LED bulb for each sensor with shrouds on both? Do you use small desk size lamps with the adjustable arms?


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PostPosted: Fri Sep 03, 2021 6:16 pm 
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I took a 2x4 and cut it 2 feet long. I mounted one light over each sensor and used apple juice cans with the ends removed for the shrouds. The 2x4 is screwed into the beams in my basement range.

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PostPosted: Fri Sep 03, 2021 6:42 pm 
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TCooper wrote:
Last night I changed the bulbs in that room to a pair of 100W equivalent LEDs. Now I can't get a Chrony reading. Is there any way to use LED lights with a chronograph? Bulbs closer, further, different wattage?
I got my first Chrony just a bunch of months ago, I struggled to make it work at first. I tried some LED lighting unsuccessfully. I did some research, I can't remember exactly, but there may be a problem with LEDs that are dimmer-capable or flash-capable. I got a pair of very basic LED headlamps, no flashing. They were on sale for like three bucks each. They're 120 lumens each. Three AAA batteries each, I got rechargeables. Works great, minimal, convenient. I left the headbands off and attached the lamps with brocolli elastics. My Chrony lives on a tripod now.


Attachments:
IMG_0362 copy.JPG
IMG_0362 copy.JPG [ 124.81 KiB | Viewed 209 times ]

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PostPosted: Fri Sep 03, 2021 7:29 pm 
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eSteve wrote:
TCooper wrote:
Last night I changed the bulbs in that room to a pair of 100W equivalent LEDs. Now I can't get a Chrony reading. Is there any way to use LED lights with a chronograph? Bulbs closer, further, different wattage?
I got my first Chrony just a bunch of months ago, I struggled to make it work at first. I tried some LED lighting unsuccessfully. I did some research, I can't remember exactly, but there may be a problem with LEDs that are dimmer-capable or flash-capable. I got a pair of very basic LED headlamps, no flashing. They were on sale for like three bucks each. They're 120 lumens each. Three AAA batteries each, I got rechargeables. Works great, minimal, convenient. I left the headbands off and attached the lamps with brocolli elastics. My Chrony lives on a tripod now.


Great idea. Looks like dollarstore lights. I think I saw them locally a couple of days ago.


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PostPosted: Fri Sep 03, 2021 7:32 pm 
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notec wrote:
I took a 2x4 and cut it 2 feet long. I mounted one light over each sensor and used apple juice cans with the ends removed for the shrouds. The 2x4 is screwed into the beams in my basement range.


What lumens and wattage for the LED bulbs? Are you using battery powered LEDs or wired?


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PostPosted: Fri Sep 03, 2021 7:42 pm 
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120v GE 800lumen 5000k
Similar to these.
https://www.grainger.ca/en/product/p/GE ... 5798815819!


3 pack at Walmart for $10

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PostPosted: Fri Sep 03, 2021 7:51 pm 
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notec wrote:
120v GE 800lumen 5000k
Similar to these.
https://www.grainger.ca/en/product/p/GE ... 5798815819!


3 pack at Walmart for $10


Thanks! Those bulbs are different. I've never noticed the cylindrical bulbs before. I could probably finds some goodies at the recycle store that would work to mount the bulbs.


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PostPosted: Fri Sep 03, 2021 8:56 pm 
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I just used construction light sockets
https://www.amazon.ca/Legrand-Pass-Seym ... 3595&psc=1

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PostPosted: Fri Sep 03, 2021 9:07 pm 
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notec wrote:
I just used construction light sockets
https://www.amazon.ca/Legrand-Pass-Seym ... 3595&psc=1


Another great idea. Thanks!


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PostPosted: Fri Sep 03, 2021 11:02 pm 
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Some inexpensive LED light bulbs that work on AC have a very simple rectifier circuit that ends up sending half-wave DC to the LEDs.... They flash at 60 times a second, just like a fluorescent tube.... and that will not work with a Chrony.....

I purchased some "compact" LED bulbs which are fluid filled for cooling.... and they work perfectly with my Chrony.... However, they were 2 or 3 times the price of the cheaper LEDs.... Some LEDs are meant to be used with a dimmer and some aren't.... It is possible one, or the other, may provide you with a solution.... I don't know which is more likely to work, unfortunately....

Light coming from a single source (eg. one light fixture) centered above the Chrony, will introduce an error in the Chrony readings.... This is because light travels in straight lines, and so the path taken by the light angles towards the sensors.... The pellet path will be shorter than if each sensor had its own light source (or the sun, 93M miles away).... This will result in a higher Chrony reading than the correct velocity....

Image

Since the pellet path is shorter when using a single light source, and the Chrony is measuring the time to travel between the sensors, the velocity reading will err on the high side.... The closer the single light source to the pellet path, the greater the error.... :roll:

Bob

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PostPosted: Sat Sep 04, 2021 12:19 am 
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I have checked arrow speeds and slingshot ammo both indoors and outdoors and didn't notice a difference in velocities. I haven't checked my airguns outside so I can't say if the velocity is different. I'll have to try it for comparison. Now I'm curious. The light fixture that I use has two bulbs but they are not directly above each sensor with tubes directing light downwards. I position the chronograph 32" below the fixture.


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PostPosted: Sat Sep 04, 2021 11:52 am 
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I just finished some Chrony testing. My P17 pistol has always been consistent with velocities so that's what I used. The pistol was freshly lubed and I shot a dozen pellets to make sure it was performing properly. The 8.44gr JSB Exact was the pellet.

For the indoor test I switched back to a pair of 60W incandescent bulbs. As you can see, the ceiling light fixture is an old style with a tinted glass cover. The bulbs point in opposite directions with a bit of a gap between for the sockets.

Inside Test
388, 385, 385, 386, 386 - Ave = 386 fps

Outside Test
383, 386, 384, 386, 386 - Ave = 385 fps

I brought everything back inside and shot a pellet indoors again and got 383 fps. The first shot indoors may have been a light pellet or a looser fit but I wasn't paying attention. There doesn't seem to be much difference in velocity. Shooting a few dozen pellets might even show no difference. I'm not trying to prove Bob wrong but possibly my bulb arrangement and light cover in the basement work fine. A different style of light fixture may give higher readings, as was anticipated. I position the Chrony 32" below the light fixture and the light does not come from the center of this fixture but rather from each end because of the way the bulbs are situated. All of this really means nothing because you have to test your own lighting vs outdoors.


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PostPosted: Sat Sep 04, 2021 1:01 pm 
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Oh, you dont have the diffusers for the Chrony........I wasnt sure how well they worked without them.

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