Many atheists are fond of dismissing the Holy Spirit as evidence of God's existence. The following remarks from a post entitled "Why The 'Inner Witness To The Holy Spirit' Is Evidence of Nothing" (Atheism And The City, 17 July 2013) is illustrative of their arguments in this regard: "It seems that some people just 'know' that god or some higher power exists because they 'feel' it, and nothing can come in their way. But it always seemed obvious to me that the fact that Christians, Hindus, Mormons and New Age spiritualists alike can all have these amazing emotional/spiritual experiences, that their experiences were indicative of nothing more than just our natural tendency to attribute deeper meaning to our emotional experiences and hallucinations." He went on to question the Christian God's existence by asking his followers "why would he be giving Hindus, Buddhists, and Muslims amazing transcendent spiritual experiences when they meditate, chant and pray?"
By now, you're probably wondering what all of this has to do with luminol? According to Tom Harris in his article "How Luminol Works" traces of human blood are revealed "by a light-producing chemical reaction (chemiluminescence) between several chemicals (C8H7O3N3) and hemoglobin." (science. howstuffworks.com) In other words, things that are not readily apparent to the naked eye are made manifest to investigators by the use of this chemical. A room that appears as though nothing important ever happened there in normal light can be transformed into a major crime scene by turning off the light!
Similarly, the opaque blackness of night can be transformed by a pair of night vision goggles (as a former soldier, I can attest to the validity of this phenomenon). Likewise, things that are not visible to the naked eye are made manifest by telescopes and microscopes.
Think about it, it wasn't that long ago that we didn't know that things like bacterias and viruses existed. To be sure, there were other indications/evidences that these microbes existed (e.g. the presence of disease). We, however, had never actually seen them.
In fact, humans find that we need assistance from many different devices/instruments in order to see or hear things that are normally beyond our natural abilities to observe. So why is it such a stretch to suggest that a "Holy Spirit" is necessary to perceive/understand things spiritual? And, is it really that far-fetched to suppose that a Universal God would make something of that nature available to guide/help/aid people of different faiths?
Why doesn't the Holy Spirit make everyone "see" the same thing and impart perfect understanding? Is that how Luminol works? Is that how a microscope or a telescope works? Isn't the performance of all of these tools dependent on the abilities of the people who use them and the techniques which they employ in their use? What do you think?