Film-Tech Forum ARCHIVE: What's the red LED radiant intensity?

This is topic What's the red LED radiant intensity? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=006887

Posted by German Marin (Member # 918) on 01-19-2005, 08:19 AM:

For the Cyan Track, what's the standard intensity for the red LED's?
Regards,
German.

Posted by Monte L Fullmer (Member # 2797) on 01-19-2005, 03:38 PM:

Basically, there is no standard of intensity for LED as long as the camera can read the cyan track, with a good error count(for Dolby) Digital) and the DTS track without no dropouts (which is mainly set by the scanner roller lateral alignment). You don't want to crank up the voltage on the LED power supply to much, or it will take some life out of the LED array much quicker.

Actually Cyan tracks are great for LED, for when you mix magenta and cyan together, you have a solid black color - which are the opposite ends of the color spectrum.

Hope this helps some. - thx Monte

Posted by John Pytlak (Member # 331) on 01-19-2005, 04:02 PM:

The amount of light needed to achieve a standard output level depends on the sensitivity and spectral response of the photoreceptor, and the efficiency of the optical system. A pre-amplifier has been necessary in some applications.

The output of red LEDs suitable for use in sound readers has a narrow bandwidth, centered near 660 nanometers wavelength, which happens to be near the peak spectral density of the cyan dye.

Posted by Michael Schaffer (Member # 1204) on 01-19-2005, 04:29 PM:

What exactly does peak spectral density mean and how does it relate to density in the sense of exposure? Does that mean that the density of the printed cyan track does not affect absolute level?

Posted by Mark Gulbrandsen (Member # 72) on 01-19-2005, 07:24 PM:

quote: Monte L Fullmer
Basically, there is no standard of intensity for LED as long as the camera can read the cyan track, with a good error count(for Dolby) Digital) and the DTS track without no dropouts (which is mainly set by the scanner roller lateral alignment). You don't want to crank up the voltage on the LED power supply to much, or it will take some life out of the LED array much quicker.

Digital:
Actually Monte for Dolby Digital there is a standard P to P level that is read with a scope of 4 volts. The operating level of the LED(or lamp) is directly related to the actual video level and there is a standard for that when adjusting a CAT 700 or 701. If it can't make 4 volts or there are large spikes in the waveform indicating dead elements then the LED is at the end of its life.

ANALOG:
Although I don't use this method on all installations as some preamps are pretty noisy this is fine for general "Shopping Center" installations such as yours and reccomended by Kelmar and others.....

For Analog the Processors solor cell GAINS are adjusted all the way up and then the LED's intensity is adjusted for proper Dolby Level with a little tweeking on the higher level channel to get it the same as the other channel. From then on the LED voltage/current(depending on whos supply you use) adjustment becomes the calibration adjustment for Dolby Level. This will assure longest LED life span. Also installing relays to kill the LED in between shows GREATLY increases LED life. I once clocked 3.5 hours in one day of dead time in a theatre that the LED could have been switched off... Times 365 days thats 1277.5 hours of dead running time on the LED for nothing. Of course you could also junk the cheap C.E.'s in favor of the BACP stuff and probably end up with the longest LED life span of all.

Monte... Also... never adjust the lateral position of a DTS Time Code reader. Adjusting it will get you no where but to having out of adjustment time code readers. Its un-necessary and you cannot put it back in its correct position without sending it back to DTS. They are the only ones that have the special DTS Lateral Position "Buzz Track" film.....

Mark @ CLACO

Posted by Monte L Fullmer (Member # 2797) on 01-19-2005, 10:18 PM:

quote: Mark Gulbrandsen
never adjust the lateral position of a DTS Time Code reader

...Shooty Darn, and I was shown this trick with the Edwards Chief Engineer when I began my term with EDWS that if I ever have to do this, for he mentioned that with time that the roller will fade a bit in the lateral sense and there will have to be slight adjustments at times....in which I had to do one at Nampa last month-unit was having a hard time reading the DTS track and I tweaked it a bit with a quarter-turn and this zeroed in the track to get a solid reading.

quote: Mark Gulbrandsen
Also installing relays to kill the LED in between shows GREATLY increases LED life. I once clocked 3.5 hours in one day of dead time...

Sounds like all of our theatres since they're doing full matinees now.

Any ideas on how to do this with the Dolby CAT-701/2 units, for I wouldn't mind researching this one out more for our theatres, since the brass got a little twisted on the LED/heat sink prices...(even though you had mentioned to me of the LED replacement itself being a whole bunch cheaper..)

thx-Monte

Posted by German Marin (Member # 918) on 01-20-2005, 04:15 AM:

quote:
John Pytlak
The amount of light needed to achieve a standard output level depends on the sensitivity and spectral response of the photoreceptor

The fotoreceptor is a Dolby Stereo cell.
Regards,
German.

Posted by Matt Zeiner (Member # 1914) on 01-22-2005, 09:50 AM:

Hi Mark -

quote: Mark Gulbrandsen
For Analog the Processors solor cell GAINS are adjusted all the way up and then the LED's intensity is adjusted for proper Dolby Level with a little tweeking on the higher level channel to get it the same as the other channel. From then on the LED voltage/current(depending on whos supply you use) adjustment becomes the calibration adjustment for Dolby Level. This will assure longest LED life span

....and the worst possible S/N ratio....no? edit- didn't see that you noted this....