Hi.

This may probably be nothing, but made me still wonder. Couple months ago. I bought 70W MH/HPS floodlight wich used Rx7s -type lamp. It came with Osram powerstar HQI-TS excellence 70 W/D daylight lamp within. Then I went to local shop and bought HIT-colorlite colored MH lamp to used with this fixture(was very expensive lamp, 80EURO). when I replaced the lamp and tested it I found the color of light(It was blue)was very lousy. I would expect more deeply blue. I mounted it to light my backyard and took it down yeasterday. Today when I opened the ballast cover, I checked the text in the ballast and found out that it says "lamp: HPS/MH 100W." the type of the ballast is SM 100 14200 and its mabe by layrton.

and the question is, Will it destroy my (expensive) colored MH in a longer run or is 70W MH meant to be used with this kind of ballast? I remember having one layrton 70W HPS/MH ballast in other fixture thou so they do at least exists. and will this have anything to do with the fact that colored MH's color was not so deep as i would liked it to bee. any guess will the color of lamp change when the lamp ages?

sorry this message became little incoherent but hope you understand.

70W MH (and SON as well) shall definitelly not be operated on "100W" ballast.
It is for sure overheated - 70W ballast deliver 1A (into 77V arc), while 100W deliver ~1.2A, so about 20% higher current. Taking into account the saturated vapor behavior (higher temperature -> higher arc voltage), the lamp might be easilly overpowered to ~120W, what would shorten it's life a lot (mainly arctube material) - the devitrification would be speeded up a lot. Together with higher operating pressure it make even the explosion more likely.

If "100W MH/HPS" ballast was used within 114-117mm Rx7s fixture, it is clearly manufacturing defect and a reason for warranty claim.

The only exception might be, then the "100W" ballast (assume series choke reactor) is rated for 260..280V mains instead of 230V, so would have same inductance as 230V 70W one. But i've never seen any (EU 50Hz serial choke) ballast designed for other voltages then 220 (old Europe), 230 (Present Europe), 240 (UK), 380 (old "delta" connected) and 400V (new "delta" connected), so i doubt such voltage rating exist.

here is a scrappy picture of that fixture http://www.whitenightcape.com/IMG_9274.JPG As you can see it clearly says 70W in the front glass but there is 100W ballast. So what kind of lamp they do use that 100W ballast? I have to find another right wattage ballast somewhere. I think this is pretty bad thing that in a brand new fixture has a wrong ballast in it. I feel like being cheated .

It was most likely manufacturing error, so you should claim it for warranty replacement...
Even the capacitor value (if i read it correctly) say 12uF, what is correct value for 70W SON/MH. For 100W it would be 15uF...

I went to that shop where I bought this fixture and complained about wrong ballast. Owner of the shop(nice old man) said that he did not have anymore those fixtures and we agree that he gave me brand new 70W HPS ballast and Id replaced it myself. He also gave me that 100W ballast so now this fixture is working correctly. Is this 100W ballast capable running a 100W white-son or will that need somekind of special ballast. I have one philips made one and lampholder for that. I also have one HPS igniter(could not find it right now anywhere) so could that be used too?

I have met this before, especially in lighting for fish tanks, where the ballast could be any wattage from 6 to 40W, mostly 20W, in a fixture meant for a small T8 lamp, generally a 15W or so lamp. Even worse is that the ballasts are enclosed in a PVC housing, with no ventilation or thermal protection, and are not designed to be opened, as they are welded shut during manufacture. I have seen many that took the lamp out during failure, and most have bulging discoloured cases.

what is the point of using wrong ballast? especially if lamp is overpowered? sell more, expensive special lamps for fish tanks because they dont last very long? My parents has a small fish tank wich has 18W fluorescent fixture with special lamp. I have never opened it because all the screws are so difficult place. Lamp has lasted pretty long. It was bought about 5 or 6 years ago and is lit 15 hours per day. so that would make about 32 000 hours. It has a preheat ballast because there is a starter. now when I heart this I became so curious that I have to go and open that fixture and see what kind of ballast there is...

Is this 100W ballast capable running a 100W white-son or will that need somekind of special ballast. I have one philips made one and lampholder for that. I also have one HPS igniter(could not find it right now anywhere) so could that be used too?

No, at least not directly. Compare to other HID's, white SON need special controller, what control (stabilize) accurately the arctube temperature, as it is very critical for the lamp performance, the lamp would not be thermally stable on regular ballast - it or end up in low pessure mode, or start cycling.
It's functionality might be explained: When the arctube temperature rise, so does the vapor pressure. Higher vapor pressure cause higher arc voltage. This voltage increase is sensed by the controller, what does correction by reducing the ballast current, so the power delivered to the lamp. Lower power to the lamp mean the temperature return back. This system ensures the arctube temperature, so gas pressure are kept constant, even when the lamp ages (tube blackening convert some light into heat, so tend to increase the temperature) or over mains and ballast parameters tolerances and at last it ensure the lamp heat up into correct temperature state.

@ aquarium fluorescents:
  Fluorescent tubes do not care, what are exact ballast characteristic, when it deliver correct current (except for starting, when sufficient OCV or voltage spike is needed to start). This allow to use one ballast type for wide range of lamps, e.g. 0.17A 230V ballast could run all T5 lamps up to ~25W, all PL-S (5..13W), all PL-C up to 25W, even series combination of lamps above, only correct starter types should be used and total wattage should not not exceed ~18W.
What should be observed is the minimum lamp wattage rating for series reactor, as using lower wattage lamp mean higher voltage is across the ballast, so when you exceed designed limit, it's core might saturate and cause high current spikes, so lamp stress and ballast overheat.