When changing out the light bulbs in your metal halide or fluorescent bulb setup, be sure to cut back on the photoperiod of your aquarium to prevent corals from getting burned and from being subjected to photo-inhibition. As bulbs age, they experience a significant drop-off in PAR numbers and their spectra will shift. The corals will adapt to this lower light, but whenever new bulbs are put in place, the PAR jumps significantly. This can cause instant damage to coral tissue, but fortunately this can be prevented. By cutting back on the photoperiod, the corals are exposed to less damaging light and can better adapt to it. As the days and weeks go by, the photoperiod can be increased more and more until it’s back at its normal time.