Jacksta 40W 500K Induction Lamp

Induction lamps have always been expensive.  So I was rather surprised to see this pop up on eBay for thirty quid.  After a brief internal debate, I decided that even if it was truly dire it was worth grabbing for curiosity value if nothing else, not least because it was a truly bizarre looking piece of tech.

First reactions upon its arrival were "Goodness this thing is odd" followed by "This thing is heavy."  Not really surprising that it's heavy given the chunky transformer used to couple the power into the discharge vessel.

The next real observation is that for a 40W lamp, it's huge.  You're certainly not going to be using this thing in table lights...or many ceiling lights unless they've got completely open shades - and are very well screwed into the ceiling.  Being honest though, this lamp is more industrial than residential, so that's probably not a huge issue.  The only orientation I'd really worry about it in would be horizontal as the weight would result in that putting quite a lot of strain on a little E27 lamp holder.  Given that it's also "planar" in shape, you would have to make sure that the lamp holder was oriented correctly or most of your light would end up going in the wrong direction.  Really does look to be intended for cap up use though.

The other thing I've noticed is that the ballast appears to be free to rattle around in the lamp base.  This seems somewhat of a recipe to me for wires or components getting knocked off in shipping (assuming that it's not loose due to a clip breaking in shipping or something like that) and doesn't give a particularly good impression when you first pick it up and it rattles.  I'd like to get into it and take a look at the ballast, however haven't figured out a non-destructive way to get into it yet - the base is actually quite solidly fixed onto the orange portion.  Sadly I can't afford to buy one of these just to tear it to bits, or it would probably make an interesting YouTube video for us techie types.

I have to admit to being slightly puzzled that this apparently 40W lamp only draws 33W even when fully warmed up.  I tend to think that there may be a common ballast in use here for the 30W and 40W versions of this lamp, with the discharge vessel or the transformer windings being the only difference between them.  This practice is quite common with compact fluorescents, so nothing to say the practice might not be the same here.

Despite my gut feelings being that this is very much a generic Chinese built lamp which appears with any number of different labels stuck on it (the fact that said label was actually not properly stuck on this one when I got it helping suggest that...), it seems to work all right.  It's a bright little sucker that's for sure, quite effectively drowning out a 30W CFL I ran it next to - even though the colour temperature difference didn't help in making that comparison.  The light distribution is pretty good too thanks to the shape of the lamp, helping increase the amount which is radiated from the lamp crown.

The shape of the bulb itself deserves some mention here, simply because it is so utterly strange.  At each end, where the electrodes would be if this were a CFL, the tube is already quite wide with a 1.5" (T12 in linear fluorescent terms or 38mm) diameter, but this quickly bulges out into an oval cross section with a diameter in the wide axis of around 90mm, and 50mm in the narrow axis.  In appearance, taking on somewhat of a hybrid appearance between the Philips QL and Osram Endura...I'm honestly not sure what to make of it!  I've tried to capture this thing from a number of angles, but I don't think it will ever come across in the photos quite how peculiar it actually looks.

The established tube diameters have been come to over a large number of years of research and experiment, coming to a balance between current density and the problematic fact that mercury vapour is opaque to its own radiation.  UV radiation production is most efficient with a very low current density (which of course favours a very large tube diameter).  However, if you increase the tube diameter, this then results in a larger portion of the radiation produced being absorbed by the vapour itself, reducing the amount of it which reaches the phosphor on the tube walls.  Some clever ways around this have been tested over the years, two classic and instantly recognisable examples being the "PowerGroove" tubes made by General Electric, which had large indentations (effectively giving the tube a crescent shaped profile), and the "PowerTwist" tubes as made by Duro-Test (which used spiral shaped indentations along the length of the tube).  These are all different methods to increase the surface area of the tube, but without actually increasing the diameter to excessive levels.  I do find myself wondering if the tube design seen here, may have gone somewhat into that "too far" category, given that the quoted efficiency level of 58Lm/W is pretty low compared to the norms for both compact and standard fluorescent lamps these days.  It's also possible that the phosphor mix may be responsible for this if the quality is not quite up to that as used by the more major manufacturers.  If that's the case lumen maintenance over the claimed 60,000 hour lifespan may also be rather a worry.

That lifespan is mainly going to be dependant on the quality of the drive electronics.  This is the bugbear of compact fluorescents to a large extent, especially the cheaper ones.  Often as not, the ballast will go pop long before the tube is worn out.  While the tube in this may be capable of lasting effectively indefinitely (albeit of course with ongoing lumen depreciation), the electronics will definitely have a finite life - and that life will depend on several things including; quality of the components used, thermal management and over-voltage protection.  Actual construction quality also plays a part of course, as a duff solder joint will kill a lamp just as easily as a component failure.  Sadly on many Chinese products these are all points which are often partly or completely overlooked. This leads to devices which have the potential to last for many tens of thousands of hours instead failing very early on.  The ballast in this case, without having looked at it doesn't immediately strike me as being all that bad.  The RF interference radiated by this lamp is far lower than that of many CFLs, only having any effect on SW, MW or LW radio if it's brought within a foot of the receiver.  This is helped by the drive waveform apparently being a pretty clean sine wave at 250KHz (this was measured by wrapping several turns of wire around the discharge vessel to act as an antenna and using this to drive the input to my scope).  The ballast also seems to run fairly cool even after several hours.  By far the hottest area being the metal cover over the antenna winding around the tube.

I'd really like to be able to get into the ballast of this thing and also be able to do a proper runtime test of it.  If at some point in the future finances permit I might consider picking another one up to be dismantled, examined, then set up on a run-it-till-it-dies test - has been years since I did one of them!

An interesting lamp.  Not totally sure what its target audience is given that it's level with a big CFL in terms of output, is far and above the price of said CFLs, and is far larger and unwieldy which means it won't fit in anything other than either open or low bay fixtures really.  Most domestic applications where the "fit and forget" lifetime would be a bonus are precluded simply because of the sheer bulk of the thing.

It's an interesting one for sure...and I like it for that, but I'm struggling to actually come up with a use for it!

Jacksta 40W 500K Induction Lamp - General overview

Jacksta 40W 500K Induction Lamp - Showing rear of lamp and cap

Jacksta 40W 500K Induction Lamp - Detail of the transformer winding used to couple energy into the discharge

Jacksta 40W 500K Induction Lamp - Detail of heat-isolation gap in lamp base to attempt to manage ballast temperature

Jacksta 40W 500K Induction Lamp illuminating my workstation from approximately two metres

Jacksta 40W 500K Induction Lamp - Shown while alight

Jacksta 40W 500K Induction Lamp - Held in hand to give relative sense of scale

Jacksta 40W 500K Induction Lamp - Detail showing unusual shape of the discharge vessel (1/3)

Jacksta 40W 500K Induction Lamp - Detail showing unusual shape of the discharge vessel (2/3)

Jacksta 40W 500K Induction Lamp - Detail showing unusual shape of discharge vessel (3/3)

Jacksta 40W 500K Induction Lamp Output Spectra

Jacksta 40W 500K Induction Lamp - Detail of sticker on lamp base

This lamp added to the Virtual Display Shelf on the 6th July 2012 at 21:49.

References: Lamp markings and manufacturer's webpage.

Acknowledgements: None.

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19th June 2023: Changes to page formatting to improve readability on mobile devices.  Also made some background code changes to improve search engine behaviour.