LIGHT - A UNIQUE ILLUMINATION
Without light, there can be no life. Natural and spiritual life both depend upon it. God's first creative act was to bring light into a scene of dark chaos: "And God saw the light, that it was good" (Gen 1.4). Also, He has delivered us spiritually from "the power of darkness" (Col 1.13) and made us "light in the Lord" (Eph 5.8).
To be effective, light requires at least three things - a source, a receptor, and no barrier in between. The primary source of every kind of light is God Himself: "God is light, and in him is no darkness at all" (1 Jn 1.5). If God had not sent "the true Light" into the world (Jn 1.9), we would have been lost in the darkness for ever. How grateful we ought to be that "the darkness is past, and the true light now shineth" (1 Jn 2.8), and how diligently we ought to "let (our) light so shine before men", without barriers (bushels) so that people around us may see our "good works and glorify (our) Father which is in heaven" (Mt 5.15,16).
But this light will be ineffective if no one or nothing receives it. Sad to say, Satan has blinded the minds of those who do not believe "lest the light of the glorious gospel of Christshould shine unto them" (2 Cor 4.4). But the gracious and great Physician who opened many blind eyes while He was here on earth, and gave clarity of vision (Mk 8.25), continues to do so still by the power of the Holy Spirit and through His servants (Acts 26.18; Eph 1.18). May the example of John the Baptist inspire us, to be a "burning and a shining light (lamp)" (Jn 5.35), not the source of the light but bearers of it, voices crying, signposts pointing (Jn 1.23,29), preaching not ourselves, but Christ Jesus the Lord (2 Cor 4.5).
What is light?
The light to which we are accustomed every day is a special and unique form of energy, coming from certain natural or artificial sources and received by our eyes. The resulting information then registered in our brain is very complex and rich in content. Variable colours, shapes and intensities all convey different meanings. Of all our senses, sight is the one which gives us most information about our surroundings.
Light is a form of radiation, which really means it is radiated or emitted from some high energy source. For life on earth, the commonest and most important source is the sun. Its heat warms us, its light sustains us and enables us to learn and discover what is around us. But that great source would have been ineffective if the light had been blocked somehow, or if we (and other life forms) were not equipped with efficient receptors of the light which arrived. In fact, the characteristics of these receptors (our eyes) match the light source exactly, and what is in between is not a barrier but an effective filter for the light. It is another example of a wonderfully designed scheme in which we can trace the wisdom and skill of our Almighty God.
What we call light is a very small section of a huge spectrum of radiation called electromagnetic waves which travel at the incredible speed of 299,793 km/sec. At one end of this spectrum the radiation has very long wavelengths. These are the radio waves with wavelengths up to several kilometres, down to microwaves of about 1 cm wavelength. These carry very small amounts of energy. At the other end is the very short wavelength radiation, the X rays and the gamma rays, which carry large amounts of energy. In the middle is the visible spectrum, made up of colours to which our eyes are sensitive, the familiar "colours of the rainbow" with all their beauty. Beyond its red end with a longer wavelength lies the infra red, and beyond its violet end with a shorter wavelength is the ultraviolet. We cannot see either of these but we can feel the effects of both, one as heat, the other as that which tans our skin when exposed to the sun.
All types of radiation exist throughout space, but we and other life forms on earth can use only the light in the visible spectrum. Just as importantly, we need protection from the other radiation. The longer wavelengths are harmful to life (the microwaves), and the shorter wavelengths are lethal because their energy is so great they would and do break up our cells and tear apart the molecules which compose them. Isn't it amazing that earth receives very little of these harmful wavelengths, whilst receiving large amounts of visible radiation - which is just a tiny fraction of all the types which exist! The Creator and Sustainer of life on earth makes it happen in the following way.
First, the source, the sun, has the correct temperature of 6,000 degrees C for it to emit most of its radiation in the middle of the visible range. It does also emit some in the near infrared which provides the significant heating effect for earth, and some in the near ultraviolet which is utilised in some other processes. God created a sun which would emit radiation with the exact wavelengths which life on earth would require. We have already seen how the sun gives the earth the correct temperature for life to exist, but now we notice that its radiation is the very type that our eyes respond to. In addition, it is the type of radiation which drives reactions in our environment to provide basic food supplies, in processes which are called photobiology or photochemistry.
Next, as the radiation arrives at the outer boundaries of the earth, some is filtered out by ozone and by water vapour high in the upper atmosphere. What is filtered out is most of the short wave ultraviolet and, by another mechanism, most of the higher energy gamma rays from outer space. Most of the longer and harmful microwaves are also absorbed, so that only the most useful and beneficial radiation reaches the earth's surface. So a barrier of water vapour is in place to protect earth from most of the harmful radiation, but it is no barrier to the life-giving light because water does not absorb visible light.
What coincidences! - entirely different processes: one in the sun millions of miles away, the other here on the earth, and another example of the uniquely beneficial properties of water. "O Lord, how manifold are thy works! In wisdom hast thou made them all!" (Ps 104.24).
Water and light
This interaction of light with water also benefits aquatic life. The harmful ultraviolet which does reach the earth's surface is quickly absorbed in the very top few millimetres of the water, protecting those many organisms and creatures which live in the seas, lakes and rivers. But the visible light essential for photosynthesis is not absorbed and can penetrate down to about 100 metres.
Infrared is also absorbed in the top layers of water, heating them from the top, so that they become lighter than the lower layers. The warmer water therefore remains near the surface where it can transfer heat to the air, influence the climate, and help to maintain steady temperatures. If the heat had gone down into the bulk of the water, this could not happen.
Sight and light
The eye is a remarkable structure, operating in a way similar to (but much better than) a modern camera. Light is focused on the retina and registers a signal by a tiny photochemical reaction. Only the wavelengths of visible light can trigger this reaction other wavelengths would not do so.
Furthermore, the size of our eyes gives optimum performance and clarity of vision with the wavelengths of visible light. Longer wavelengths would have required much larger eyes to do the same - if wavelengths were ten times greater, the "eye" would need to be about 25 cm in size. On the other hand, shorter wavelengths would be absorbed in the fluids of the eye, and even destroy its biological tissue and the photoreceptors on the retina. The size requirements for clear vision using light from the sun are found in our eyes which are not grotesquely too big for the head, nor too small to be insignificant.
Whilst we do "walk by faith, not by sight" (2 Cor 5.7), sight and light are wonderful gifts from God. May no clouds dim our vision. May we walk in the light, as he is in the light (1 Jn 1.7). May His Word always be a lamp to our feet and a light to our path (Ps 119.105), for in His light we shall see light (Ps 36.9).
To be continued.