Is "visible" light, actually visible? Claiming that visible light is called visible light and therefore it must be visible, is circular reasoning. This question is not about the definition of visible, because in that regard, light shows none of the characteristics of visible objects. Light is in fact, what makes objects visible.
Now I'm not talking about wavelengths we can't detect or even light that doesn't strike our eyes. I'm specifically referring to detectable light that strikes our retina. Many will see this as a futile argument about definitions until they actually grasp the differences and realize the implications.
The purpose of vision, what gives us an evolutionary advantage, is that it allows us to see things. For those unfamiliar with the concept of indirect realism, here's a link. http://cns-alumni.bu.edu/~slehar/webstuff/book/chap1.html . What we see are objects, like predators, food and possible mates. These objects exist in objective reality (outside our heads) but we perceive our brains representation of these objects in our subjective reality (the reality we perceive inside our heads).
DETECTION IS NOT PERCEPTION.
Our eyes detect light, but detection is a mechanical process of which we are not directly conscious of. We can deduce that the process is occurring due to the fact that we see objects and understand the visual process. Seeing something, on the other hand, is a conscious process. We sometimes don't even see things which are right in front of our eyes and I don't mean figuratively. Have you every moved something out of the way while looking in the fridge, when the thing you're looking for is the thing you moved? Seeing is not perceiving. Perception is consciously seeing something. Detection is not perception.
DO WE SEE OBJECTS OR LIGHT.
The most common held belief is that we perceive light, not objects. As far as detection goes, that's true. Our eyes detect light that strikes the retina. This begins the physiological aspect of vision. Phototransduction, electrochemical impulses travelling to the visual cortex via the optic nerve, the subconscious creating visual representations and sensations. All these processes are subconscious. It's only then that conscious perception comes in. And what we consciously perceive are the objects, from which the detected light, originates. So we do not see light, we see the (brains representation) objects.
LIGHT, LIGHT AND LIGHT.
Light, the word, has many meanings and this adds to the confusion of whether we see light or not. We have heavy and light, darkness and light, electromagnetic radiation and figuratively, seeing the light, which represents comprehension. We can see if something is heavy or light. We can see brightness. But brightness is not a property of electromagnetic radiation. Brightness is a sensation, like colors. If colors are the interpretation of lights wavelength, then brightness is the brains interpretation of lights amplitude. Now many people believe seeing light (brightness) is seeing light. That if you shine a laser into your eye, you're seeing light. In a sense, they're right. We are perceiving brightness. But this brightness is a result of our cones being -saturated. If you look at a 60w globe and hold your gaze steady, your eyes will adjust to the brightness. After a few seconds you begin to see the element from which the light emanates. Brightness is an obstruction, preventing us from seeing the object itself. Brightness is phenomenal in nature. Not a property of light itself.
SEE AND SEE.
The word see, too has different meanings. The expression "to see the future " has two interpretations. One as a psychic, having visions of the future, and one as a visionary, able to predict future trends. To consciously perceive or to consciously conceive. So we can see "conceive " light but not perceive light.
WHAT DO WE ACTUALLY DETECT?
A photon is a boson particle. It can't actually be detected. What we detect is when a photon strikes something. It's the collision we detect. At the moment of collision, a photon no longer exists. Everything we know about light, is deduced by detecting these collisions. Light itself is undetectable. It neither emits, nor reflects anything which would allow us to detect it.