Infrared or red light "tells" the plant that it is daylight; extra red or infrared will cause the plant to produce shorter internodes; and thus the plant should be a bit shorter and bushier the more red light it gets. The absence of red light "tells" the plant it is dark.
I don't see any down side to using infrared heat lights to warm your greenhouse, except maybe the cost.

Well it was quite cheap and it is a white heat lamp bulb not red like the ones they use over food. I guess I'll try it out tonight and see how it goes. I will need a higher wattage though.

I got the 125w bulb but the area to heat is about 5Lx6Wx6H

The ceramic socket can handle up to 300w bulbs

Here is a link that might be useful: Philips Heat Light 250W