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LED Wood Lamp

I've found myself typing and repeating this enough i thought i should probably break it out to its own page.

some pics you will see on this site have a blue-purple look to them. I had been doing UV lithography when the mold issue hit. Teaching myself about that process i came across other things UV light is used for, one being disinfecting rooms/tools/w.e. another being used by doctors and vets to identify some strains or species of fungus and some other conditions. wood lamps/uv emitters also have found use in forensics. 

I quickly threw this together from what was my vacuum pulldown uv lithography exposure unit. 





as a side note this used a 4.1w 375nm uv led/emitter. when i built this end of 2017 or even more so when i ordered this end of 2016 for my uv litho box....




it was 2014 or 15 that uv led emitters became high power and affordable for even medium sized biz. they had until around then been either lab experiments or obscenely priced. part of the issue is uv tends to break apart plastic/the device destroys itself. there are more complex issues at play that i wont go into but i figured it was worth noting i put this together in a hand held version in 2017 while id assume today in 2020 most hospitals are still using something like this. 


 in like 1969 or 70 if I recall right but blue is the opposite end of the spectrum and UV tends to eat plastic there's other more technical issues but high powered UV LEDs that aren't anywhere affordable for an individual or even a small business that's at Best of five-year- old development. This light has more power than any of the wood lamps I saw at a doctor's office I assembled it I parted it out among other things that could have been profitable I would bet they're starting the phase  make these available to doctors offices rather than the old fluorescent tubes. When the bleeding hit in the apartment I was doing a hundred things that once but I was well on my way to an LLC which I can tell you any day of the week how to do that top of my head put another article about that and probably link it here.


the reason for the voltage display on the side has to do with lithium-ion battery chemistry. this is two 3.7v nominal cells in series. ie plus to minus makes 7.4v for the majority of the use/discharge. a single cell starts at 4.2 and by the time its down to 3.2 you should stop using it. I was using unprotected cells meaning alone they dont turn themselves off. 

I had installed a china/ebay battery management/cutoff board meant for 2 in series. hopefully this behaves in a way where if either cell drops bellow 3.2 the pack turns off. 

as the device was $2 from china i trust it about as much as one should trust a toddler with a lighter surrounded by cans of gas. hence as a back up i installed a voltmeter on the pack. ..still working on leveling holes in plastic lol.
  


the reason you cut them off or they cut off around 3.2 v (some 3 or 3.1 dependent on chem variant) is things called dendrites tend to form. think stalactites in caves but inside your battery. if these short plus to minus on the inside... you go note 7/battery spontaneous disintegrates itself. thats sort of a joke but at one time i read that was the industry's preferred term (spontaneous disintegration).

in theory the metal can cells (like 18650s and the 21700) have a pressure release valve under the anode/+ side. I once read some statistics on how reliable/otherwise that is... maybe its changed... i dont want to find out. 

why that valve is important... the difference between a pipe bomb and a rocket motor? the later has one side open.
the wood lamp used a two cell pack. its whats warpped in tape in the pic way at the top. this is a makeshift 4 cell pack but the limiter board (right pic) and cells /batteries in the pack are the same. the limit/cutoff board is however specific to a 2 cell pack.. I just dont have a better pic of that pack to post here. 
the board visible is a general purpose DC to DC converter that happens to feature a CC mode. CC is constant current. LEDs are current mode devices and have this nasty tendency to drop in resistance as they heat up. an inefficient solution to ensure the led doesnt burn out is place a resistor in the loop. see led current limiting resistor. the better way to go about it is a power supply that can be dialed in to a max current, aka CC mode. 



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