In the world of DNA research there are studies of genes that “turn on” or “turn off” at particular moments in the sequence of fetal development. Depending on what comes before and after the gene being expressed, how long that state of on or off persists, and the chronological moment (early or late) for a particular gene expression alone (and with reference to co-occurring, coordinating genes that are being expressed), the results in the creature being born can vary widely. See also, https://en.wikipedia.org/wiki/Spatiotemporal_gene_expression
Looking at theses similar photos of bright yellow summer flowers much of the structure and context of the subject is the same, despite using different cameras about 36 hours apart. But one is overcast light from the east on a morning of rain showers to come and the other comes earlier in the week at evening with the westering sun backlighting the stems and flowers. Although the analogy stretches a bit thin, this example of changing light producing very different results is something like the DNA description, above, in which genes are expressed (or suppressed) differently in one person and the other, one guppy and the other, one pine tree and the other. The essential structure of the plant in this photo collage is unchanged, but the visual experience of overcast (indirect) light that is weak versus direct light that is strong could not be any more different.
Just as the addition of a strong spotlight, or less dramatically the addition of fill-light (artificial or by use of reflectors of the natural, ambient light), will affect the viewing experience in a location-specific, time-specific way —now standing out; now blended into surroundings, so, too, of genes in “spatio-temporal expression” (Wikipedia, above). In other words, the same location or featured subject can take on very different character, according to changed lighting. Things like the season (angle to the horizon of the sun’s course), the weather and atmospheric conditions, the time of day, position of light in relation to the subject (back, front, side, indirect or direct lighting), and the presence (or absence) or artificial light can dramatically affect the mood, atmosphere, and overall “look” of the composition.
In a studio, the lighting can be arranged to taste for intended effect. But out of doors at a fixed location or while drifting in a photowalk, the lighting conditions are usually in flux. Some photographers are particularly keen on long shadows of early and late in the day, others are excited by twilight, with some who like rain and mist, and a few who hunt photos at night. As such, very often when in the field, there is an element of serendipity when light catches the eye and calls out to be framed in a composition for others to see. The moment of discovery or noticing a picture hiding in plain sight adds special thrill or feeling of receiving an unexpected gift. Therefore, the changing conditions of light on the subjects in front of the lens shares something with the DNA gene timing: turn on the factor and the resulting form or functions changes. Turn on the lighting condition at a certain place-and-time (spatio-temporal) and the resulting portrayal of the subject changes.
Every day and all around the path one takes through the waking hours the lighting conditions are changing. Passing by a ordinary place most days, the subjects go unnoticed. But when conditions momentarily “turn on” with bright light or a break in the weather, then that spot is transformed for a time into something out of the ordinary, a time out of time. Extending to the realm of thinking these observations about how the unremarkable suddenly can be transformed for a moment or two, there is a new book by Kerri ni Dochartaigh called Thin Places about trauma, cultural landscape, and memoryscape. A location can unexpectedly trigger memories that blur into the present and/or future and/or past in such a way that what once was sharply separated with thick spacing now changes to very thin boundaries that divide past from present and future; what is tangible from what is living within one’s mind. This same observation about the ordinary suddenly or slowly shifting in appearance (light turned on or off; genes turned on or off) seems equally true of the life and terrain of the mind. If a thought is triggered by external events, chance meetings with others, or the momentary brush with an idea in book or radio or online video, then what previously had lain dormant or unfertilized now can change and grow. In the presence of a catalyst, the germ of an idea now can grow, thanks to the co-occurrence of circumstances, context, and adjacent conditions.
In summary, whether it is a change in light (photography), a change in gene expression (spatiotemporal), or the emergence of an idea and its communication to others for further transformations and permutations, all of these instances spring from impulses that occur in exquisite timing, order, and duration to make what before went unnoticed, unarticulated, not expressed to become now something completely different and capable of causing subsequent ripples in what others may receive, perceive and conceive. Stated in the most personalizing terms, each human life is a kind of temporary “gene expression” that co-occurs with others in specific times and places that can catalyze glorious (or dreadful) results along the way; now turned on, now turned off. So it is worth paying attention to those times when a shift in light can make a dull scene come alive.
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