Measuring light output from xenon flashlamps.

Hello,

We have 3W xenon flashlamps which flash once every 800ms

The flash looks to be quite long, but in fact the tube current flows literally for just ~200us for each flash.

Recently, we doubled the trigger voltage (making it correspond to that required by the tube) and the light output appears to have gone down by 40%.

However, i suspect that its our light measuring equipment.

The higher trigger voltage, i believe is making the flash of higher current , but shorter lasting, and i believe our light measuring equipment misses the shorter duration flash.....and gives a low reading.

What equipment do you recomend for measuring the light output in our case here?


I do not have access to the darkroom till the engineer gets back and thats two weeks, -so i cannot even say what equipment we have.

I think you can use Optical power meters

Or (think I mentioned it before), a CCD and iris might do the trick.
Something like this.
CCDs are good at this job. I'm no optics/CCD expert though..

https://www.neutronoptics.com Looks like they sell only X-ray cameras I did not see optical range there.

Use a basically linear sensor, e.g. a photodiode.
Attenuate the light to an intensity level that gives validated linear sensor output with continuous light, using a grey filter or by increasing the sensor distance.
Monitor the intensity waveform with an oscilloscope.
Measuring the true current and voltage waveform at the flash lamp would give interesting information, too.

Increased pulse current can in fact reduce light output, e.g. by capacitor ESR effect.

ok thanks, i imagine that a measuring device which can accurately measure light output when the flash only happens for 200us every 800ms is going to be very expensive.?

FvM i see what you mean but we have a standard way for measuring where the lamp has no diffusor over it and is operated at full power...its making things too complicated for our staff to have to attenuate the light and then measure it.

Als, if there was more current then wouldnt it have likely have been more because ESR was less?

FvM i see what you mean but we have a standard way for measuring where the lamp has no diffusor over it and is operated at full power...its making things too complicated for our staff to have to attenuate the light and then measure it.

Click to expand...

I guess you would want spend as much effort as necessary to achieve reliable measurements. Please notice my comment about "validated" linearity. The mentioned measurement methods are neither expensive nor difficult to perform, but require a minimum understanding of optic laws. Unfortunately this may be a problem for a commonly educated engineer...

It may be the case that the suggested photo diode measurement will work without noticeable linearity degradation at "full power". I never tried. The point is to verify this property before trusting in the measurement.

I also think that the suggested lamp current and voltage measurement is a good tool to monitor it's operation conditions.

Have you considered chemical actinometry? The only specialized equipment you need is a photometer to measure the amount of product produced. Here is the Wikipedia link for an overview. Scroll to chemical actinometry.

https://en.wikipedia.org/wiki/Actinometry

John