The reflector should be bigger and deeper than the bulb to be effective. It doesn't look safe either. I would also change it.
It doesn't have to be the wire cage one. You can get another reflector one like that one, just bigger. They have them cheap at Walmart and home depot. You don't have to get a "reptile" one at the pet store. Just make sure its a porcelain base (the part you screw the bulb into) rather than plastic and its max wattage is equal to or less than your bulb.
Take this from an electrician . You need to check the fixture ratings . If you have a one hundred watt lamp you will need a fixture rated for the lamp wattage and amperage. So if that lamp is a 150 watt I would get a 200 watt fixture . So the lamp is up in side of the reflector. If you put a 150 watt lamp in a smaller fixture you will over heat the fixture and open your self up for a big fire hazards . Every fixture has a rating for this reason. Any heat type of lamp needs to be in a porcelain base . Plastic will melt and may start a fire.