 Because the U.S. Food and Drug Administration (FDA) biases tests against UVB, the TE may make a weaker lamp appear stronger by having more UVB.Furthermore, although tanning beds are rated with exposure times, tanning lamps are not because beds can vary widely as to how a given lamp affects the user, making it difficult or impossible to compare the total UV output of different low-pressure lamps.The UVB to UVA ratio percentage is considered a technologically outdated form of measuring a lamp's overall UV output and Wolff "Metric" now lists actual UVA, UVB and total UV flux powers.