Manufacturer: Timeguard - distributed by Homebase
Model: TGNL15
Application: Night time low level illumination/security lighting
Wattage: 3W (Too low to measure reliably with my wattmeter - probably around 1W really)
Width (max): 52mm
Length: 97mm
Tube Length: 55mm approx (10mm diameter), linear
Bulb/Tube material: Glass.  "Daylight" phosphor coating on inner wall
Colour Temperature: 6400K CRI: Ra Unknown
Peak output wavelength: Broadband emission
Total light output: Very little.
Rated lifetime: Not stated
Cap: Standard UK 3-pin plug
Operating voltage: 230-240V AC 50-60Hz
Operating current: Not yet measured
Warmup/restrike time: 5 minutes/none
Cost (original): 2.99 (late 2005) from Homebase superstore
Value (now): Unknown
Place of manufacture: Note stated
Date of manufacture: Unknown, code 0346 on back of unit
Lamp Status: Working
Notes: Okay...so it's a complete fixture rather than just a lamp...but that's not the point!  It contains a very interesting lamp, so I say it's going here...and it's my website!

I picked this up thinking that it was a rather bulky EL based nightlight, as I wanted to nick the panel for something - what precisely I cannot remember.  The reason this one was picked (price aside) was that it looked considerably more dismantlable than the others I'd seen, which I thought increased my chances of getting what I was after out in one piece.  I figured there was an EL panel in here curled into a cylinder.  How wrong I was!  Imagine my surprise when I prised the little diffuser off to find not an EL panel, but what actually appeared to be a tiny fluorescent tube.

I've since discovered thanks to some feedback however that it's really rather more interesting and unusual than that however.  Initially, I'd assumed this to be a very, very small hot cathode fluorescent tube, because to be honest that's what it looks like - hence why this used to be in the linear fluorescent section.  There are V shaped tungsten electrodes at each end of this lamp, and a long exhaust tip off halfway down the one side which contains the mercury dose.  Directly underneath the peak of the V of the electrodes is what initially I thought to be a leadwire which I assumed was used to aid starting (similar to the starting electrode in many mercury lamps), as it is electrically connected.  Now the operation of this lamp has actually been explained to me - the purpose of this makes a lot more sense.  The lamp atmosphere I have been advised is a typical low pressure neon/argon mixture.

How this lamp actually works is as follows.

At each end of the lamp,  neon glow discharge is struck between that central electrode I mentioned earlier, and the tungsten filament.  However - the lamp it set up in such a way that there is an overall potential between the electrode set at one side of the lamp and the electrode set at the other - this results in a net current flow along the full length of the tube (the neon discharges providing plenty of ionisation of the gas filling to allow that to take place with a relatively low voltage - my measurements indicating only around 30V being required to maintain it) - and due to the mercury vapour present, a fair amount of shortwave UV to be produced, exciting the phosphor on the lamp wall.  It's a very interesting idea - only really suitable for very short tube lengths, but it allows a little cold cathode tube like this to run directly from the mains with a very simple ballast, and no need for a starting pulse in the order of kilovolts.  The power usage is also very low as a result, and in theory, the tube should last really quite a long time.   Definitely an interesting little bit of technology.

In operation, it's certainly nothing you'd use in a lighthouse, but that's not what it was designed for.  It provides quite enough light to see your way safely around a room or down a hallway without walking into things (in the case of my room, bits of car, or vintage television - doing this has caused me a very painfully stubbed toe on more than one occasion before!...and a broken height control potentiometer on a 1968 Kolster-Brandes KV024 television).  It's certainly considerably brighter than your garden variety neon nightlights by an order of magnitude.  The cool, daylight-like white may not be to everyone's tastes though, especially for this sort of application.  It does make a room feel cooler when lit by this thing, rather than the friendly red-orange glow typical of your little plug in neon nightlights.

The lamp seemed very prone to flickering wildly when first started up, but after "burning in" for a few hours, it seems to have settled down nicely.  The only flicker being that derived from the mains frequency (due to the simple capacitive ballast).  The whole unit gets barely warm to the touch, even after being left running all night.

I don't think this is one lamp that I'd put into service in a children's bedroom though, for one main reason, the way it's put together.  While the body itself is securely screwed together, the little plastic diffuser on the front is only clipped in position.  While it is clipped in quite securely, I'm pretty sure that given some time or the right tools, determined little fingers could get it off, potentially exposing live parts.  A situation that really does not bear thinking about.  I'd far rather see an adhesive of some kind under this part just to make sure that it stays put.  Granted though, this was not advertised as being for children's bedrooms, but that's where everyone immediately thinks of when they think nightlights.  For low level nighttime lighting of a hallway or something though, these little things are ideal.

Click Thumbnails for full size images.
 

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This lamp added to the Virtual Display Shelf on the 21st August 2006 at 22:44.

Page last update: 9th August 2009.  Corrected information on operating principles of the lamp, re-categorised it, and tidied the page up a little.


References: None.


Acknowledgements: Many thanks to the website reader who dropped me a line explaining how the tube in this unit works.