Arduino Forum

Using Arduino => LEDs and Multiplexing => Topic started by: amundsen on Nov 18, 2012, 10:44 am

Title: Using UV LEDs as source for visible violet ?
Post by: amundsen on Nov 18, 2012, 10:44 am
Hello,

I want to have a light of deep purple color. I have ordered some violet LEDs bet one could qualify the color to be indigo blue at best, not violet.

According to Wikipedia, wavelengths between 420 and 450 nm can be qualified as indigo. Therefore, is there any other solution than using UV LEDs to get a true violet color ? Looking at data for several UV LEDs, it seems they do also produce light in the visible wavelengths. However I'd be happy to have confirmation from some users that the violet colour is visible enough to be used for this purpose. Also, is there a realistic solution to filter the UV and let only the violet go trough (I don't want to damage my eyes) ?

Thank you in advance.
Title: Re: Using UV LEDs as source for visible violet ?
Post by: John_Smith on Nov 18, 2012, 11:04 am
I used blue LEDs to flouresce red tape, with the UV content, be careful even with the blue ones and your eyes !
Title: Re: Using UV LEDs as source for visible violet ?
Post by: MarkT on Nov 18, 2012, 11:10 am
Purple isn't violet.  Purples are a mixture of blue and red.  Having said that a good violet LED is definitely violet looking and will cause fluorescence (you don't need UV to fluoresce red/orange dyes BTW).  I bought a mixed batch of cheap LEDs from eBay a while back and the violets are good ones - I have no way to easily measure the wavelength though (!)
Title: Re: Using UV LEDs as source for visible violet ?
Post by: Hippynerd on Nov 18, 2012, 05:37 pm
Violet is purple. purple isnt ultraviolet though.
(https://lh3.googleusercontent.com/-dP97a_af0ms/UBsh6aAy0nI/AAAAAAAACvo/KlfgYvZV4C0/s640/IMG_20120802_175619.jpg)
This is a single UV LED with some aluminium foil tape on it to focus the light forward. It looks quite purply here in this photo, but its not as purply in real life. These LEDs do produce light that is in the human visibilty range. If you want purple, you probably want to mix blue and red, infact, you may need to muck about mixing color to get what you want.

LEDs do not filter light, they produce light at a very specific narrow frequency.
Title: Re: Using UV LEDs as source for visible violet ?
Post by: johnwasser on Nov 18, 2012, 05:53 pm
Lumex makes an LED with peak output at 400 nm:

http://www.digikey.com/product-detail/en/SSL-LX5093UVC/67-1830-ND/480547
Title: Re: Using UV LEDs as source for visible violet ?
Post by: Grumpy_Mike on Nov 18, 2012, 07:55 pm
Use a white LED and a colour filter of your choice.
Title: Re: Using UV LEDs as source for visible violet ?
Post by: amundsen on Nov 18, 2012, 09:37 pm
In between I have found this supplier, which has a choice of different 5mm violet/indigo (not specifically-UV) LEDs: http://shop.strato.de/

Thanks for your answers guys !