One of the church buildings I handle the indoor lighting at had originally a MH bulb shining up on a steeple.  The bulb failed after about a year (on a photocell) and the person who replaced the bulb obviously put in a HPS bulb because of the orange/warm white color now.  I do not have a ladder tall enough to get up there at present to examine things closer, but I was thinking, would it be possible for a MH ballasted fixture to light a HPS lamp?  The reason for asking is that I am thinking the guy just found the closest wattage he could to replace the old MH bulb with and put in a HPS bulb as there was a large collection of them in the central light closet.

Thanks

Ryan

If the arc voltages and rated current are at least similar, the probe start MH ballast may run the HPS.
This is the case of most European HPS (they could replace the MH of the same wattage; better say pulse MH's were designed to run on the same gear as European HPS) and at least the US 150W S56 (on the M102 ballast).

I do believe the original MH bulbs were 150 watts so thanks for the info.  I really want to get the MH bulbs back in there, the white lights on the steeple make it look MUCH better than the HPS right now.  Will try to get some photos.  Thankfully the MH bulb in the fixture that shines up on the flagpole is still going well. 

If the HPS is geting about the same power, there is no problem for the HPS. (actually HPS tolerate quite well small under / overpowering - better than MH and i think even better than mercury). You can evaluate it by the HPS color - if looks normal, probably ok. If SOX'ish orange or looks like it never warmed up cmpletely, underpowered. If whiter than normal - overpowered

Though if the ballast current is higher then there is very severe problem for the ballast

European HPS and MH on pulse start are working on the same gear (for lamps of the same power)

it certainly looks more orangeish and not warmed up completely.  I think I'm gonna go switch the thing off until I can get up there and get the right lamps back in there. 

Horrible night time cell phone picture.  The Steeple has the HPS lamps and then you can see the flag pole light which has the MH lamp.  Gotta get the MH lamps back into steeple fixtures and also see if the photocells are broken or covered as they are day burners.  

it certainly looks more orangeish and not warmed up completely.  I think I'm gonna go switch the thing off until I can get up there and get the right lamps back in there. 

The question is, if he did not used the S55 instead of the S56 lamp...

I will be climbing up there this weekend to find out, if the weather is good. 

I have seen this commonly done in the US - I don't know why someone would not notice the major change in colour but I guess some people really don't care (and HPS lamps are cheaper, often easier to find and tend to last longer).

In the medium base fixtures in the US - HPS is ALWAYS 52-55 volts, so a MH lamp of the same wattage in an HPS fixture won't start but an HPS in a MH fixture will work, only be somewhat dim & yellow. The ballasts seem to hold up but I think from what Medved said in answering one of my questions, they would run hot.

S56 (100v, 150w) fixtures seem to be very rare noawadays...I have yet to come across a 120v version. It makes sense to use the 55v ballast on 120v as no step-up is required. The S56 lamp is also a mogul-base ED28/BT28 - a larger bulb than the S55.