Plants show signs of stress when light levels are too low or too high. Weak, spindly growth indicates insufficient light. Variegated foliage will lose all or part of its markings. Signs of too much light are bleached or wilting leaves on plants like scheffleras, philodendrons, ferns and peperomias. In this case, move plants farther from the glass or filter light with a sheer curtain.
Most houseplants originate in tropical or semitropical regions, where the air is moist.
With insufficient humidity, leaves turn dull and papery. Brown leaf tips are another common symptom. Another option is to place a humidifier in the room where most of your plants are located. There are several other ways to raise the humidity around plants. Grouping plants keeps the moisture level higher than if air freely circulates around each plant.