It’s more than light,

because it’s
more than an aquarium

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Philips CoralCare LED fixture

The unique features of CoralCare Gen2 are:

Wide spectral range - For excellent coral growth, and natural reef appearance.
Perfect light balance - Unique homogeneous light distribution and color mixing solution. Our innovative design features 68 carefully positioned LEDs to mimic the optical effect of sunlight.
Easy to control - Control your CoralCare easily and wirelessly, with control over two distinct lighting channels, and preprogrammed schedules.
Quality & reliability - The new, slimmer design is energy efficient, has passive cooling and a long lifespan.

The perfect light balance

When sunlight enters a water surface, so-called caustic patterns are projected on the ocean floor (see Fig. 1). Such projected patterns occur when the light is highly collimated (such as from the sun or a narrow beam spot) or when the source is very small (like an LED). Large diffuse sources, like an overcast sky, conventional TL tubes or light via indirect lighting, do not produce caustics.

Fig. 1 Caustics caused by sunlight projected on the ocean floor

Traditionally, aquarium lighting has been based on two main technologies:

Metal Halide (HID/HQI)
Metal Halide (HID/HQI) was commonly used to illuminate reef aquaria. The single high powered light source (up to 1000W) produces strong caustic effects, which correspond to the dynamics found in natural reefs.

Fluorescent lighting
T5 tubes were the most commonly used light source. The T5 Tube is a homogeneous linear source that produces negligible caustic effects.

Most aquarists prefer balanced light dynamics that is achievable by combining both technologies. (T5 is considered to be too flat/still and HID to be too dynamic)

Fig. 2 Colored pattern produced by caustics and colored LED sources in an aquarium

Towards LED lighting

In aquarium lighting, LEDs have the benefits of high efficiency and easy spectral tune-ability. Various wavelengths of LEDs may be combined to compose a spectral lighting quality as known from traditional lighting. However, the array of colored point-like sources may result in a restlessly moving caustic pattern in the aquarium, accompanied by dynamic color patterns and colored shadows (see Fig. 2).

LED lighting, when designed well, enables an ideal balance between (natural white) light dynamics, good color mixing and a homogeneous light distribution.

While the dynamic caustic patterns may be appreciated inside the aquarium to some extent (since it is caused by the water dynamics), part of the light may also leak out of the aquarium and create a restless pattern on the floor nearby. This is a very disturbing effect and occurs when LEDs are used without an optical system. More specifically it takes place when light enters the water at an angle above 63 degrees to the vertical direction (illustrated in Fig. 3). Since water has a relatively low refractive index (typically n=1.34), light at these angles is not reflected by total internal reflection and it can refract out of the water volume and land on the floor.

Fig. 3 Light with a large angle (>63 degrees, dashed arrows) to the vertical direction may leak from the sides of the aquarium and project restless caustic patterns onto the floor. Light at smaller angles stay within the aquarium by total internal reflection at the sides of the aquarium (solid arrows).

Fig. 4 Scalloping in the aquarium (indicated by the yellow arrows) is caused by the use of collimated light sources with a hard beam cut-off. The highly directional light also produces high contrasts on objects in the aquarium (red arrow), i.e. the object modelling is poor.

A solution to keep all light within the water volume is to limit the light to beam angles well within 63 degrees to the vertical direction (e.g. by placing collimator lenses on each LED). While this directional lighting is more efficient (more light stays inside the aquarium), it also has some drawbacks: directional light produces so-called scalloping on the back side of the aquarium (alternating bright and dark light pattern) and unattractive modelling of the objects within the aquarium (too high contrast between top and bottom parts of an object, with loss of visible shape details in both the bright and the dark side of the object). Both effects are illustrated in the picture captioned figure 4.

Also the growth of the coral is affected by the beam form of the applied light. In addition to contrast differences, intensity differences also result in deviating growth speeds. If a coral is lit with a narrow beam, the coral will grow in a narrow structure only towards the light. When more homogenous light is applied, most coral species grow in a more treelike structure.

Fig. 5 - Picture 5 shows a seriatopora caliendrum frag that has stood under narrow bundled light for some weeks. The top part of the coral is growing healthy, but the bottom (inner) part of the coral is showing some necrosis (yellow arrow). This is because Insufficient light reached the inner structure of the coral and that would have been prevented if the light spread would have been more homogeneous.

The CoralCare optics aims to achieve a balance between all above mentioned aspects:

• It blocks the direct view to the LEDs if above a cut-off angle of 63 degrees
• It redistributes the light beyond the cut-off angle via a light scattering element
• It allows most of the light with angles smaller than the cut-off angle to pass without scattering, or with much less scattering.

• With CoralCare Gen2, sharp white colored caustic patterns are allowed thanks to the 4 clear areas in the optical plate. This mimics the natural light patterns when selecting daylight color settings.

The main idea is that the projection of caustic patterns on the floor may be reduced or completely removed by blocking the light at high angles. Still, since the light at high angles is needed to avoid scalloping and bad modeling, the light is first scattered to create a larger virtual source. However, it will come from a large source and create blurry projections that will be less noticeable than sharp caustic patterns.

Component details

A unique patented co-extruded light guide (see Fig. 6) is added on top of the CoralCare LED array to create the necessary cut-off angle to reduce caustics.

Above the cut-off angle light is captured by a light guide and consecutively scattered in all directions by a white reflective layer on the light guide.

Fig. 6 Optical system CoralCare Gen2 including LED pcb, co-extruded lightguide, diffuse glass plate and clear zones in glass plate.

This result in the light distribution is depicted in the figures below

Fig. 7.1

Fig. 7.2

Fig. 7.3

Fig 7.1 shows the direct light from the LED, featuring the 63 cutoff angle created by the optical light guide.

Fig 7.2 shows the diffusely reflected light that is coming from the light guide.

Fig 7.3 shows the summation of both the direct and diffusely reflected light as applicable in the CoralCare product.

Glass plate

After various user-tests the caustic effect inside the aquarium was still considered to be too dynamic. As stated above, the caustic effect can be reduced by increasing the source size. The virtual source size may be increased by applying a diffuser in front of the source.

The cover plate abrasion is tuned to scatter the light just slightly, in order to provide an increase in source size without compromising (i) the optical efficiency, and (ii) the beam cut-off needed to suppress disturbing caustics outside of the aquarium.

With CoralCare Gen 2, four carefully placed clear areas (Figures 6 and 9) were added in the glass plate. These clear areas allow the light emitted by four white LED’s to directly exit the glass plate, adding some extra sharp dynamic light effects on top of the homogeneous blanket of diffuse light. Because only the 4 white LED’s can directly penetrate the glass plate, the caustic patterns have a natural warm color point. The link between caustic pattern and the color point is inspired by the natural effects in the ocean. At noon, when the sun is at its highest point, the light creates sharp caustic patterns on the ocean floor. During this time the light has its shortest travel distance through the water before it arrives at the ocean floor (Fig 8.1,8.2). It is known that the longer the light travels, the bigger part of the spectral content (especially the green/red colors) is absorbed. Therefore, the warmest color point is linked to this period of the day. During the evening, the travel distance increases (creating a more blueish color point in the water) and the light is scattered further. The scattering patterns caused by the sun are drastically reduced.

Fig. 8.1 The effect of sunlight on the ocean floor.

Fig. 8.2 Natural light patterns

Disco effect

The severity of the disco effect (colored shadows) is significantly reduced by the optics.

All light (from each individual LED and color) angles >63 are coupled in the light guide. Within this light guide, all colors are mixed and re-distributed in a diffuse, broad pattern. This light is added (summed up) to the direct light (with angles <63 degree) resulting in a source with a more homogeneous colored distribution.

Advantages CoralCare optical system:

• Drastically reduces caustic effect outside of the aquarium (>63 degree beam angle)
• Light >63 degree is captured in light guide and scattered into a broad diffuse light distribution that do not produce caustics.
• No optical loss of light <63 degree between source and target.
• Significantly improves the color mixing of LED engine (see Fig. 9)
• The lightguide increases the source size, resulting in balanced caustic effects.
• Suppresses majority of sharp caustic patterns but selectively allows sharp patterns from 4 white LEDs to create natural light patterns when selecting daylight color settings.

The chosen architecture results in an ideal balance between efficiency, uniform light distribution in the aquarium, color homogeneity and the right level of light dynamics.

Fig. 9. CoralCare Gen2 optical guide

It’s more than light, because it’s more than an aquarium