Neon Sign in Visible/IR/UV

[alanb]

I spent some time around some neon signs and decided to see how they looked in UV. In a room lit with a mix of tungsten, compact fluorescent, and neon, the neon signs were by far the brightest UV sources.

 

I picked a Bud Light sign for some tests. Not the best beer but it was the most colorful sign.

 

Visible light. All these are balanced to 3000K. Camera is a full spectrum Canon EOS M3, lens is a EL-Nikkor 75mm f/4. ISO 100, 1/80 s, f/8.

 

 

RD1000 deep IR filter. ISO 400, 1/4 s, f/8.

 

 

LifePixel's 850nm deep IR filter. ISO 400, 1/60 s, f/8.

 

 

Hoya R72 IR filter. ISO 400, 1/100 s, f/8.

 

 

LaLaU UV filter. ISO 400, 1 s, f/8.

 

 

Whatever gives the red color is also blocking a lot of UV. There are other odd points - for example the leftmost stroke of the B is slightly dimmer in visible and UV, but significantly brighter in all three IR photos.

[Cadmium]

Oh Cool! These are quite nice and interesting. Great shots. :-)

[JMC]

How interesting. I'd assumed that different colours were only from different gases (neon for orange/red and argon for blue), but apparently that is not always the case. Some tubes are painted or coated to produce different colours, and also with some mercury is added to intensify blues.

 

If there is a bit of mercury in the blue ones, that might explain why they look so bright in the UV compared to the red one (given the strong mercury line around 365nm).

 

It's not unusual to see differences from one end to the other. Plasma physics and chemistry is a fickle thing, and curves or even imperfections in the glass can have an impact on what is going on and what wavelengths are emitted.