If you reflected all the infrared light, the efficiency would be 100%, since all the light leaving the bulb would be visible. Normally, the vast majority of the

If you reflected all the infrared light, the efficiency would be 100%, since all the light leaving the bulb would be visible. Normally, the vast majority of the light leaving the bulb is infrared, but if you keep 90% of it in the bulb, then 6.6% of the light leaving the bulb is visible light.