Many of the epistemological issues that occupied natural philosophers of the seventeenth century were expressed visually in title-page engravings. One of those issues concerned the relative status to be accorded to evidence of the senses, as compared to knowledge gained by faith or reason. In title-page illustrations, the various arguments were often waged by a series of light metaphors: the Light of Reason, the Light of Nature, and the Lights of Sense, Scripture, and Grace. When such illustrations are examined with the authors' theological views in mind, it becomes apparent that in the first half of the seventeenth century, Catholic authors favored the Light of Reason as a source of truth, while Protestant authors favored the Light of Nature. Since by the end of the century it was widely accepted by scientists of all religious persuasions that certain knowledge must be grounded in sense evidence and the direct study of nature, one might argue that in this instance Protestantism was responsible for nurturing an important development of the Scientific Revolution. However, the skewed nature of the sample (the Catholics who used light metaphors were mostly Jesuits; the Protestants who did so mostly alchemists) and the large number of counterexamples available (many Catholic scientists believed in the ascendancy of the senses but failed to engage in metaphorical warfare) mitigate against taking this offshoot of the Merton thesis too seriously.