Instructables

USB Powered UV Light

Hi,
I would like to build a germicidal lamp which is powered by USB for a school assignment that I'm doing and I was wondering if someone could help.

I did a search on a trading site to see the type of  lamps and there seems to be 3 types, cold cathode, quartz and ones which actually look like bulbs.

Which type can be easily wired so that it can be powered by a USB port?

Advice will be appreciated.

egrayton (author) 2 years ago
I actually spoke to my teacher now about the difficulty of getting a UV light working on USB so he told me that I could use a 12v DC power source as my input as long as I keep power under 2w.

This was pretty easy as there are many suppliers on alibaba who provide 1-2w ccfl with 12v ballast and I guess that it should be easy enough to attach the ballast to the power source.

I've already sent a couple of messages to suppliers to see if they can help.
Goodhart2 years ago
It appears to be an industrial item at the moment. I found several suppliers; mostly from mainland China, and most of them with a MAX forward voltage of around 6.8 V. At every site I visited, they had a signin and a place to "inquire" about prices.
egrayton (author) 2 years ago
The LED in the link won't help because the wavelength of the UV needs to be 254nm, the one in the link is 380nm so it won't have the germicidal effect.

I'm pretty sure that a 254nm led will cost too much money as they are made for specialised research in science and medicine.
I was able to find this one but there is no price listed, its a single LED, and it needs about 7V @ 20mA to operate. I suspect any others you will find will have similar power needs. So you won't be able to power it off USB. Any other lighting option you find will also have high power needs that USB won't be able to support.
http://www.alibaba.com/product-gs/543796971/254nm_uvc_sterilization_Led_for_killing.html

You will want to use UV LEDs. You need to have at least 30 minutes of exposure time to be effective.

Here are some good ones.
http://www.superbrightleds.com/moreinfo/component-leds/5mm-uv-led-15-degree-viewing-angle-380-nm-30mw/632/1907/?utm_source=googlebase&utm_medium=base&utm_content=RL5-UV0215-380&utm_campaign=GoogleBaseChild

Seems most UV LEDs run at 3.5V @ 100mA. Seeing the max that most PCs offer a USB power is 5V with up to 500mA you'll be limited to using only 4 LEDs. The image below comes from a good LED calc and shows the wiring you'll need for it. That setup will use 400mA. IS you wanted to push things you could use 5 LEDs but then your maxing out the USB port and not all PC/laptops offer a full 500mA to the USB ports. Some max out at 200mA. In which case the lamp wouldn't work at all.
LEDs.jpg
Jayefuu2 years ago
Powered by USB you'd probably have most success with a UV LED.