Lanterns/Fixtures > Modern

Small size fixture = Early Cycling: May not ALWAYS be a factor...

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Jace the Gull:
I am starting to believe it is not always 100% a factor....Just because it is 250 watt HPS in a small fixture doesn't always mean it will have a early cycling.  What puts me into this.....

There's an intersection near me that has had construction in early 2000.....and BGE had installed 250 watt medium sized fixtures on wooden poles while the county had installed aluminum poles with 250 watt small sized fixtures.....all of them GEs....medium ones are GE M-400A3 with sag lens and the small ones are GE M-250R2 FCO.....I am not sure what lamps was used in the smaller ones but I will find out with my mega zoom camera....the medium ones of course had Philips Altos....They were installed roughly around the same year...

Guess which group started cycling first???

SeanB~1:
The Alto's of course...........

Medved:
@Jace:The size of the fixture alone is responsible for the temperature of the air inside, what may be 40degC for bigger or 80degC for the small fixture. This 40degC look like huge difference, but it remain as the same absolute temperature difference for all components inside. So for reliability of the ballast and/or ignitor it is significant difference, you have to remember, then the arctube run way above 1000degC, while the 40K difference remain the same even here - and 1000 vs 1040degC is nearly not any factor compare to other things, what influence the arctube temperature. By the way this fact is the reason, why HID's seems to be insensitive to the outside temperature - the outside temperature simply does not vary in the view of the arctube...
Way more important is the shape of all heat reflective surfaces - how much of the heat radiation they redirect back onto the arctube - these may shift the arctube temperature easily by few 100's degC and this then has large impact on the lamp characteristic.
Very strong factor are ballast load characteristics and tolerance and it's response to mains variation.
And last, but not least all factors, that affect lamp aging: Switching frequency, burning time per day, current crest factor, lamp itself,...

Jace the Gull:

--- Quote from: SeanB~1 on November 07, 2010, 12:28:35 AM ---The Alto's of course...........

--- End quote ---

I donno what lamps the smaller fixtures had...but yes you are right the bigger fixtures started to cycle first...the smaller ones still has original lamps and hasn't started cycling

Medved....it may be that the smaller GE may not have an issue on cycling and have better lamps......but with smaller Cooper fixtures....they have serious early cycling problems, but it doesn't seem to be an issue on smaller GE fixtures as far as I have seen since the bigger ones with SAME wattage a few of them already has started cycling while the smaller GE hasn't started cycling yet. But it is unknown what lamps the smaller ones have since different company installed them......but they are same wattage as the big ones!

Medved:
@Jace: The most important difference, but nearly not possible to see from the outside, is the exact reflector shape and positionning.
As i wrote, the cycling problem (now assume same lamp, ballast and mains voltage) is not much related to the size, but the exact internal shaping. So indeed, some big fixtures may have problems, as well as some other small, but another small might be fine.
Of course, the lamp lifetime is a huge factor, i would say (with the mains fast fluctuation) are the dominant factors, except if the optic is really badly designed.

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