What determines whether a 100-w light bulb cost more to use than a 1200-w hair dryer?

The cost of using a 100-watt light bulb versus a 1200-watt hair dryer is determined by their power consumption and the duration of use. While the hair dryer uses significantly more power, its operational time is typically much shorter than that of a light bulb. To compare costs, you would calculate the energy consumed (in kilowatt-hours) for each device based on their wattage and usage time, then multiply by the cost per kilowatt-hour from your electricity provider. If the hair dryer is used for a very short period, it could still end up costing less overall despite its higher wattage.