Street Light bulbs and ballasts question

Hello. I am replacing some bulbs in the street lights in my neighborhood. They are about 12-14 years old, and most appear to have 175watt metal halide ballasts, but the bulbs are 175watt mercury vapor. I have replaced several of the 175watt mercury vapor bulbs with the same type, and all appear to be working OK. Recently, I replaced a 175watt mercury vapor bulb with a 100watt mercury vapor bulb (still using the 175watt metal halide ballast that is installed). I was surprised to see the brightness did not appear to change noticeably, and it has been installed a couple of weeks now.

My question....is there any reason I shouldn't replace future 175watt mercury vapor bulbs, as they burn out, with the 100watt mercury vapor bulbs, continuing to use the 175watt metal halide ballast? There is a significant money savings in the cost of the bulbs, and I assume in the amount of electricity consumed. Any advise appreciated. Thanks.

Mercury vapor bulbs can last a long time. That said, that 100W bulb is going to have a real short life with a 175W ballast. Though it has been a few weeks, that is likely <150 hours of operation on a bulb that can last 10's of thousands of hours. Your eye cannot notice even fairly large changes in light output (25%), so it could already be rapidly depreciating. It is likely using close to the same power as the 175W bulbs.

MV is going to get harder and harder to source since many areas have banned them to some degree.

While they last a long time, their lumen depreciation (how fast they get dim) is quite quick. Sure they could last 100K hours, but by 12,000 hours (3 years), they have probably lost 30-40% of their light and should be replaced.

A 100W MH puts out as much light as the 175MV, but you will need to replace every 3-5 years.

If you're not going to consider an energy retrofit, why not consider the Philips All Start. I've personally used these in parking lots where a better performing lamp was desired. The one you would need is 145W and works on the standard M57 ballast. It is a ceramic MH lamp, with a CRI of 85+, and a rated life of 20,000 HRS.+.

As to what SemiMan said, he is on the money. MV lamps are going away, so consider your options for better lighting. (MV fixtures were outlawed some years ago.)

ron6962 said:

....is there any reason I shouldn't replace future 175watt mercury vapor bulbs, as they burn out, with the 100watt mercury vapor bulbs, continuing to use the 175watt metal halide ballast?

Click to expand...

Besides the life issue that Semiman describes, there's the potential for "non-passive" arc tube failure. This is industry speak for exploding arc tubes, which can penetrate the glass bulb as well. No one in their right mind runs a discharge lamp on a non-matched ballast, unless they crave excitement...