mini review.

[Clive Mitchell]

I just got one of the 32 LED UV torches from ebay. It works well and
projects a very concentrated beam of near UV light. As with many of
these torches it just dumps the huge parallel array of LEDs directly
across a pack of three measly AAA cells. This means that LED current
will vary according to battery quality, type and life.

The LEDs also have distinctly different intensities suggesting poor
forward voltage matching.

Other than that it's a lot of fun. Just walking about your house at
night with it on reveals some unusual fluorescing objects.

The case is the usual classy machined aluminium and is chunky and nice
with a proper on-off push button.

 

[JohnR66]

What did you end up paying? How does it compare to a black light?
John

 

[Clive Mitchell]

What did you end up paying? How does it compare to a black light? John

The cost is in the "postage" but I bid for about 2.5UKP.

The beam of UV is actually very good. It would make a good UV
spotlight.

 

[Clive Mitchell]

They don't have a constant current circuit hidden in there, do they?

Nope. The current is limited by the battery impedance, the torch
metalwork and the PCB tracks, so there's not much limiting there.

Some of the ebay torches with small numbers of LEDs do use resistors,
but the big torches don't. I think this includes the torches with the
counterfeit Luxeons in them.

 

[Clive Mitchell]

I have a single white LED flashlight which runs off a single AA cell.
It has a switched mode boost type supply (necessary to get 1.5V up to
the LED drop).

They do that single AA style torch in a wide number of LEDs. I think
the biggest uses 12 LEDs.

 

[Clive Mitchell]

Quite a few lights use boost convertors to use a single cell, people
like Zetex, OnSemi and Maxim spring to mind, all have convertors aimed
at this market.

The Chinese torches that I've opened tend to use a little two transistor
booster with a small choke. A bit like the circuit in many solar
lights.