GHL Mitra Owners club

[kien]

Originally Posted by Reef Pilot

It is the surface water ripple that does it with my Radions. When I turn off the pumps, it disappears.

It is indeed the water surface agitation that does it with any point light source. It is called the caustic effect. A caustic or caustic network is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light. In our case the curved surface is the water surface as it ripples and waves. The caustics can be the patches of light or their bright edges. These shapes often have cusp singularities.

Concentration of light, especially sunlight, can burn. The word caustic, in fact, comes from the Greek word for burnt, via the Latin causticus, burning. A common situation where caustics are visible is when light shines on a drinking glass. The glass casts a shadow, but also produces a curved region of bright light. In ideal circumstances (including perfectly parallel rays, as if from a point source at infinity), a nephroid-shaped patch of light can be produced. Rippling caustics are commonly formed when light shines through waves on a body of water.

Another familiar caustic is the rainbow. Scattering of light by raindrops causes different wavelengths of light to be refracted into arcs of differing radius, producing the bow.

T5s do not produce noticeable caustic/shimmering because the light is more enveloping as opposed to being focused like a point source. In essence there is no point source of light from a T5.

LEDs on the other hand typically have several point sources. Each point source producing a caustic. The further apart the individual LEDs are the more pronounced that particular channel's (colour) shimmer/caustic will be. The closer together the individual LEDs are the less pronounced it will be.

Radion LED array:


Mitras LED array:


Kessil 350W LED array:


Caustics on the sandbed from the different LED point sources:




Again, some people will notice it while others will not and at varying degrees of noticeability. If you don't see it or you don't notice it or you're simply not bothered by it then it doesn't really matter what other people see.