Watts are a measure of energy. They tell you how much electricity is needed to power the light bulb. Candlepower is a measure of brightness that tells you how brightly will it give off light. A light bulb can be described by both, for example a 100 watt incandescent bulb(or 24watt CFL) has 127 candlepower.
Candlepower is measured in candles and is a unit of light output. It is obsolete. One candlepower is equal to the light emitted by one pure candle that has been burning for one hour. A hundred watts of electricity produces an amount of light equal to the amount emitted by one hundred candles. 1 candlepower equals 12.57 lumens.
The higher the number goes, the greater the quantity of light produced. You may have noticed that when you turn on a very dim light, it takes a few seconds for you eyes to adjust because your eyes were being flooded with so much brightness from outside sources like sunlight and other bright lights.
The candlepower of a bulb is measured in lumens. Lumen means candlepower multiplied by 10. So one candlepower would be 10 lumens (candlepower multiplied by ten).
Most home lighting devices such as incandescent lightbulbs are measured in watts and use a method called candelas to express output. Candela is the standard unit of measurement used for incandescent light bulbs. One candela equal to the light emitted by a 100-watt incandescent bulb burning for one hour.
Candelas is calculated using the simple equation: lux divided by 2. For example, 100 watts in candelas equals 150 lux, which equals 1 candela (lumen). The higher the number, the brighter it will be.
Here is another example: A 60 watt lightbulb has approximately 6.6 candelas of brightness, and a 40 watt light bulb has approximately 4.5 candelas of brightness. You may have seen high-intensity discharge (HID) light bulbs at auto dealerships or other places. They produce very bright light but use a lot more energy than regular light bulbs, so they can be tricky to measure in both candelas and watts- especially for those of us that are not used to working in either place.
Watts is energy usage and candlepower is brightness aka lumens.