I Gilded the Lily

[Stefano]

When I photographed glass with my 340 nm LED with my old Panasonic DMC-F3, the glass had a strange glow, that seemed UV-induced UV fluorescence to me: https://www.ultravioletphotography.com/content/index.php/topic/3770-340-nm-led-first-impressions/page__view__findpost__p__34040

 

But you cannot see visible or infrared fluorescence if you are blocking those wavelengths with your filter on the lens.

[ulf]

Filtering the LEDs is not needed when you are capturing UV-images.

Compare to that you do not put a filter on the sun for the same purpose. BIIIG. Filter

 

Filtering the LEDs is needed for UVIFV to avoid mixing-in VIS spillover from the LEDs with the actual fluorescence.

Then, when you are using UV-LEDs with longer wavelengths to stimulate the fluorescence, a filter for the camera with a cut on further into the VIS is needed.

 

Most / all GG glas materials but are otherwise good as sharp cut filters to eliminate violet and deep blue light from the LEDs, they can be had in many different cut-on wavelengths.

 

Tiffen's Haze filters cut UV well without that fluorescence-problem, but there are only few usable alternatives.

Their cut-on and type naming are similar to the wratten filters, 1A, 2A, 2B, 2E:

https://www.google.c...QAAAAAdAAAAABAE

[ulf]

Thanks Ulf

the largest diameter of the group of LEDs is the 395nm LEDs at 80mm & the LW U360 plate is 150mm square & is 3mm thick.

That makes the 395nm graph even more strange as 3mm U-360 reaches OD3 at 400nm and OD5 at 405nm

[colinbm]

Ulf the U360 I have was bought about 12 years ago and is not available any more and was sold as LW long wave filter for 365nm fluoro lights for mineral fluorescence it was also cheap and labelled as U360, it is poor quality glass but gives a defused light.

For the time being will filter the lens for these 3 LED lights with either BadderU for the 340nm and 365 LEDs and the SEU Gen3 for the 395nm LEDs as it is closer to 400nm cut.

For UVIVF I have a Zeiss T* UV filter which really cuts UV.

[ulf]

OK, my fault assuming that U360 was some real or similar material as the Hoya U-360.

Then your graphs might make more sense, even if I still am suspicious about the optical power level from your 340nm LEDs.

It is unlikely high for four of those LEDs.

 

What was the distance between the LEDs and the UV-power-meter when you measured it?

Was it the same for all three LED types?

 

Nice to know you have good filters for the UVIVF.

[colinbm]

The plate of LW U360 was made by Hoya but cheaply.

, now they use ZWB3 for LW.

[Stefano]

How powerful are the single 365 and 395 nm LEDs? This can help us understand how your numbers are possible.

[colinbm]

The 365nm was 3 Nemo and the 395 was 4 no brand. Also I think the 4 340nm are really only 1w each. I am looking for more a d better prices and the same are advertised as 1, 2 or 3w, you just can't trust the Chinese.

[ulf]

The 365nm was 3 Nemo and the 395 was 4 no brand. Also I think the 4 340nm are really only 1w each. I am looking for more a d better prices and the same are advertised as 1, 2 or 3w, you just can't trust the Chinese.

And by 1W each you are talking about electrical input power, right?

[Stefano]

If they are like the one I bought, they use 2.1 W of power each (4.2 V and 0.5 A).

 

The numbers you got don't make much sense to me either. A Nemo torch uses about 10 W of power. Let's assume 35% efficiency + some losses from the filter on the front and we may have 3 W of UV. Times three, that's 9 W.

 

You have four 340 nm LEDs rated at 55 mW each, so that's 220 mW or 0.22 W total.

 

You should have about 40 times more light at 365 nm than at 340 nm. That's a big difference!

 

In your measurements the 365 nm LEDs appear to have less than double the irradiation the 340 nm LEDs have.