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UltravioletPhotography

Irradiance spectra - 60W tungsten filament and 11W compact fluorescent bulb


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Following on from the post on compact fluorescenct light bulbs (here - https://www.ultravioletphotography.com/content/index.php/topic/3909-compact-fluorescent-lamp-uv-emission/page__view__findpost__p__35797), I thought I would measure the irradiance spectra from two light bulbs;

 

Old style 60W tungsten filament (of which we still have a few in the house)

11W compact fluorescent light bulb (this is probably over 5 years old, as I tried it once and hated it, so put it back in the box)

 

Spectra were measured on my Ocean Optics FX spectrometer, with a cosine corrector on the fiber, and calibrated for absolute irradiance. Probe tip was 1cm from the bulb surface. The 11W CFL was on for about 2 mins before measurement.

 

Two plots shown below, but it's the same data. Firstly, at the scale to show the 11W CFL spectra.

 

post-148-0-22468100-1590927305.jpg

 

And secondly, zoomed in so the 60W filament bulb spectra can be seen more clearly.

 

post-148-0-11602000-1590927302.jpg

 

There's certainly a good strong 365nm peak in the CFL spectra, but I didn't see anything below that (although the spectra stops at 300nm here, I measured down to 250nm). No UV with the 60W filament bulb.

 

I hated the 11W CFL bulb when I tried it. Amazing, the gaps in its output. Quite glad it went back in the box now.

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enricosavazzi
...There's certainly a good strong 365nm peak in the CFL spectra, but I didn't see anything below that (although the spectra stops at 300nm here, I measured down to 250nm). ...

There are most likely the strongest Hg lines in the UVB inside the tube, but the glass and phosphor are probably designed to absorb them. The pressure and current in the tube are probably also optimized to give a strong 365 nm line and a few other lines that are especially efficient in stimulating emission by the phosphor.

 

I have seen more continuous CFL spectra in tubes for photography (optimized for VIS) and in some UV tubes (where the phosphor emits mostly in the UVA and UVB, so the spectrum is fairly continuous in the UV except for the strongest Hg lines).

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