Beam spread or beam angle refers to the spread of light from the luminaire. This is chosen based on the task at hand and how wide the light needs to spread. Sometimes the beam spread is fixed based on the fixture's unique shape, as it is with area lighting. Color temperature is measured in Kelvin and refers to how warm (yellowish) or cool (bluish) the lighting appears to be. Most lighting ranges from as low as 2000K (which is very warm, like candlelight) up to 5000K (which is a stark whitish blue). Typical applications call for warm white 2700K light, which is most similar to that of traditional incandescent lighting. Lumen output is the amount of illumination provided or simply how bright it is. Wattage is the amount of energy used by a fixture and is an important number to keep track of. Add up the wattage of all of your fixtures or bulbs and then determine the appropriate transformer for that wattage. We recommend not exceeding 80 percent of a transformer's capacity. If you don't have at least a 20 percent buffer from maximum capacity, you will need to step up to a larger transformer. Efficacy is a ratio that compares power consumption to light output. This is measured in lumens per watt. The reason efficacy is important is because a lot of bulbs are listed by wattage equivalents, which is how brightness was traditionally understood. Because LED bulbs are so efficient, they can produce a lot more lumens while utilizing much less power or wattage. For example, a 5 watt LED bulb may have a 30 watt halogen equivalence due to its high efficacy.