Lights on Timing Devices

[Jack Stotts]

OK all you experts, does anyone have any idea how long it takes for a 25 Watt 110 Volt light bulb to illuminate. I'm wondering how accurate our clock start indicators are. That is how long is it taking from the time the clock hits zero before the light is visable to the scorer's eye? Just curious. Appreciate any help. Jack

[rbengines]

Jack a lite bulb cycles at 60 cycles a second (light speed in all reality is instant to humans) and your eyes see at 16 frames per second, depending on your reaction time it could be anywhere from 1/16 of a second to who know what. On the other hand a camera shutter speed can be 1000th of a second. Unless tied to the clock we go back to human reflexes. The NFL has cured this with instant replay, now we getting expensive. To make a long story short the scorer is the judge and they make the call. Many of time I wanted to question calls that I thought were wrong and wondered how I got away with some I thought maybe I was over. They seem to equal out.

[Jack Stotts]

Thanks Rusty. What I'm wondering is how long does it takes the filiment to glow. If it takes 1/100 of a second and you are traveling at 60 MPH which is 88 feet/sec., 1/10 of a second is 8.8 feet and 1/100 of a second is .88 feet which is 10.56 inches and that is a lot. I know it's impossible to judge it from the race boat especially when you are talking about tenths of a second and one hundreths is out of the question. I'm thinking we should be using lights which react faster than a common filiment bulb. Your thoughts.

[quicksilver96]

Light Speed

OK all you experts, does anyone have any idea how long it takes for a 25 Watt 110 Volt light bulb to illuminate. I'm wondering how accurate our clock start indicators are. That is how long is it taking from the time the clock hits zero before the light is visable to the scorer's eye? Just curious. Appreciate any help. Jack

Light travels at 168,000 ft./sec. The human element can not react to this speed.

[Jack Stotts]

Thanks. But I'm looking for how fast the element in the bulb warms up to a glow. I know as a kid we watched what lights we used in timing motors because of the slow warm up of some bulbs. Any idea on glow time?

[Bill Huson]

about three frames on a standard video camera . . .

You can videotape a bulb going on and off and see for yourself. Usually three frame from first twinkle to full glow.

We used an LED light in the vid cam viewfinder. LEDS are instantanious to the camera eye and ours.

[rbengines]

Jack I was really pulling your leg a bit. You should know that I'm no expert in any field.

[Jack Stotts]

Hey Bill, how long is three frames? I'm not a photog guy. I would like to get a time figure. Are we looking at hundredths of a second or some time frame shorter than that or what? Would appreciate any knowledge you or anyone else may have handy.

[csh12M]

Hello Jack,

Bill is right about two to three frames, however the frame rate seems to depend on the VCR you are using. We have gone through two in our club and you could tell a difference between them. The new one seems to have less frames per second than the old one. I would guess this is because of the shriking demand for VCR's. Each frame seemed to equate to around 2-3 feet. With the old VCR you could always see the first glow in the filiment of the bulb and that was what we always used to call jumpers. With the new VCR sometimes you see the glow and sometimes you just see the bulb fully lit. So you may be giving some drivers a 2-4 foot cusion. We are looking into going to an LCD this season to solve that problem.

Dean

[les]

Bulbs, LEDs, and VCRs

Jack,

I hate being the geek in this thread, but I have to know this kind of stuff for a living - here it goes:

I believe the reason you have not gotten a straight answer is that there is, to my knowledge, no "standard" for a 25W, 110V, off the shelf bulb. Element temperature, Metal composition, And the element's inductive impedance would be the predominate factors.

On top of those numbers, a 110V system that is not synchronized with the incoming power source will suffer a plus/minus 8.3 millisecond range from the phase error from input to output source alone, at 60 Hz. If your powered from an A.C. generator, expect additional phase error.

Sam mentioned an LED system - This is far more predictable in turn on time, as the LED's capacitance and breakover voltage is far more stable over time than any A.C. bulb. Temperature is still a factor, but far less significant due to the relative area that generates the actual light emission compared to a 25W bulb.

Using a VCR as an input device has a whole different, but quantifiable, and workable set of errors. - Depends on the VCR device.

Hope this helps, email me some specifics if I have not put you to sleep with the tech stuff yet.

[Jack Stotts]

Les, thanks for the good info. I think, with you guys' help, we have made a case for not using a normal light bulb for determining when the clock hits zero. It has some delay which is to the driver's disadvantage. LEDs are much better. Thanks to all for their input. Jack

[Bill Huson]

I'm convinced . . .

I believe there was originally a little trouble seeing the LED in the camera's field of view due to the different light levels of the boats on the water and the LED. This was solved by mounting the LED in a white bottle cap to shield it a little - but had the added effect of lighting the inside of the cap making the red lighted area much larger than the LED itself.

Boat racers kick royal tail when it comes to *creative* engineering and on-the-spot problem solving.

[brian]

The real deal

Here is some info and an excel sheet I made up. Had to put it in word to upload, but I can email you excel fromat.

Dan can you add Excel sheets to the valid extentions?

Video cameras come in two different image capture formats: interlaced and progressive scan. Interlaced cameras record the image in alternating sets of lines: the odd-numbered lines are scanned, and then the even-numbered lines are scanned, then the odd-numbered lines are scanned again, and so on. One set of odd or even lines is referred to as a “field”, and a consecutive pairing of two fields of opposite parity is called a frame.
A progressive scanning digital video camera records each frame as distinct, with both fields being identical. Thus, interlaced video captures twice as many fields per second as progressive video does when both operate at the same number of frames per second. This is one of the reasons video has a “hyper-real” look, because it draws a different image 60 times per second, as opposed to film, which records 24 or 25 progressive frames per second.
Progressive scan camcorders such as the Panasonic DVX100 are generally more desirable because of the similarities they share with film. They both record frames progressively, which results in a crisper image. They can both shoot at 24 frames per second, which results in motion strobing (blurring of the subject when fast movement occurs). Thus so, progressive scanning video cameras tend to be more expensive than their interlaced counterparts. (Note that even though the digital video format only allows for 29.97 interlaced frames per second [or 25 for PAL], 24 frames per second progressive video is possible by displaying identical fields for each frame, and displaying 3 fields of an identical image for certain frames. For a more detailed explanation, see the adamwilt.com link.
Standard film stocks such as 16 mm and 35 mm record at 24 or 25 frames per second. For video, there are two frame rate standards: NTSC, and PAL, which shoot at 30/1.001 (about 29.97) frames per second and 25 frames per second, respectively.


LEDs light up very quickly. An illumination LED will achieve full brightness in approximately 0.01 seconds, 10 times faster than an incandescent light bulb (0.1 second), and many times faster than a compact fluorescent lamp, which starts to come on after 0.5 seconds or 1 second, but does not achieve full brightness for 30 seconds or more. A typical red indicator LED will achieve full brightness in microseconds, or possibly less if it's used for communication devices.


Good links:

http://www.100fps.com/

http://en.wikipedia.org/wiki/Light-emitting_diode