Fluorescent-BLB IR emission

[Guest]

In a timed series of images, I found that the IR emission from two 40W BLB fluorescent tubes decreased over time, reaching an apparent minimum after about five minutes of warm up.

 

Test method:

• Take a photo of the test scene in timed intervals from the startup of the light source
  
• Record the mean luminosity value from each of the images
  
• Plot the values by luminosity vs time
  

Conclusion:

The IR output of this bulb type appears to peak within seconds of startup, then drops off by about 88% by 300 seconds, with only ~1% further decrease seen up to 600 seconds. Whether this is useful for any particular UV imaging is entirely dependent upon the requirements of the photograph and the equipment being used. It does show that IR is much less of a potential contaminant to UV images if the bulbs are allowed to fully warm up first.

[colinbm]

Thanks for this info Mark B)

Col

[Andrea B.]

Very nice experiment, Mark. Thank you! (I love this stuff!!)

 

Do you have a way to check whether there is any Visible output and if so, does it also fade after warm-up??

[Guest]

There certainly is visible light output from this type of bulb. A tiny peak at 404 nM gives these bulbs their characteristic deep violet color, although this is just a very small fraction of the total output. I have never seen any noticeable shift in this visible output in a warm vs cold started bulb (I haven't actually put that to a test though).