Thorn SON-TD 250W

A nice 250W SON-TD fully warmed up. This lamp took rather long, approximately 18 minutes to run up.Interestingly the lamp voltage did not rise high enough to bring the lamp to its rated power. This something I have observed now with a few brand new SON lamps...

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Comment 1 to 8 of 8

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FrontSideBus

[03 May, 2026 at 10:29 AM]

You may wish to try this in a fitting and repeat the test. They suffer when ran in free air IIRC.
I've got a 1000w SON-TD which I have never ran up because I don't have a big enough luminaire!

Alex

[03 May, 2026 at 10:31 AM]

easier said than done, i will need to build/convert a fitting for it, as i have nothing in that direction.

FrontSideBus

[03 May, 2026 at 10:33 AM]

Any enclosed 1000w halogen fitting should do. The larger 400w SON-TD's will fit 1500w halogen.

AngryHorse

[03 May, 2026 at 01:09 PM]

Yes, it’s strange how free air affects these lamps, you would like to think they would be the same as their halide counterparts?

Lightbulbfun

[03 May, 2026 at 01:26 PM]

as mentioned these SON-TD lamps need to be run in an enclosed luminaire, they actually have gas-filled outer envelopes which exacerbates the free-air-running issue, any fixture for a 1000W 189mm Halogen lamp will work well, as the 250W SON-TD was designed to retrofit into those fixtures

if you dont have a suitable fixture for it, James documents the IEC test rig for them on my 1000W SON-TD upload here

FrontSideBus

[12 Sep, 2026 at 08:47 PM]

I've just been playing with a 400w GE SON-TD in a Thorlux Starflood. It ran up to about 50-odd volts and then stopped for a while, presumably as the air inside the fitting began warming up. It then started running up again until it reached about 380w and took an absolute AGE for the lamp voltage to rise that last few percent to reach 400w! The fitting was almost smoking hot by that time.

Ash

[12 Sep, 2026 at 09:03 PM]

A plateau in thermal behavior suggests something like phase change of a material or activation threshold of some other balancing mechanism. Air convection does not change its behavior within the temp range of the outer envelope of a SON lamp

dor123

[13 Sep, 2026 at 08:49 AM]

Strange that my Osram NAV-TS 70W Super 4Y, have vacuum rather than gasfilling like this one.

Comment 1 to 8 of 8

Page: 1