These are the MH bulbs I have been using with my HPS ballasts. The pic shows the box whch states it is a conversion bulb for HPS ballasts. Ive only used these type of MH bulbs in a few different brands and if the box dont say its safe for HPS ballasts then I wouldnt use it on one.
This link will tell you more about them:
http://www.tradewindsgarden.com/site/products/bulbs/product_pages/smconv.html
For those not wanting to click the link here is a copy and past of it
Quote
The Magic of Full Spectrum White Light From Existing HPS Fixtures
- Converts HPS to Metal Halide
- Compensates for the blue spectral deficiencies of HPS
- Compatible with standard HPS ballasts and ignitor systems
- Provides rich blue output for bushy vegetative growth
- Long life
SUNMASTER Conversion Grow Lamps are Metal Halide lamps which operate on standard HPS ballast and ignitor systems. The Neutral Deluxe version emits balanced light similar to a 4000° Kelvin source, while the Cool Deluxe version emits light similar to a 7000° Kelvin source, imitating the natural look of daylight.
SUNMASTER Conversion Lamps are effective in promoting both vegetative growth and flowering. They surpass the HPS lamps they replace in PAR watts - the most objective measurement of total light energy available for photosynthesis.
SUNMASTER Conversion lamps are available in 250 watt, 400 watt, 750 watt and 1,000 watt versions, with a choice of universal or base-up burning configurations for optimum performance, as well a warm, cool, or neutral colour spectrums.
SUNMASTER Conversion Lamps set new standards in general plant lighting, promoting high levels of photosynthesis without compromise.
End Quote
They are yet to impress me but im still goin to give them a chance next time to see if there is any improvements.