It’s more than light,

    because it’s
    more than an aquarium

    Philips CoralCare LED fixture


    The unique features of CoralCare are:

    • Wide spectral range - optimized for coral growth and natural reef appearance
    • Perfect light balance - unique homogeneous light distribution and color mixing solution

    • Low energy consumption thanks to highly efficient LEDs
    • Easy to control - By intelligently combining various LEDs with different wavelengths, we have simplified the set-up of the lighting controller for the user. As a result, the user only needs to select the desired color point and intensity, without having to worry about the optimal light quality for coral growth and beautification.
    • Low maintenance - long-life robust design and materials
    • Easy to install - driver integrated in fixture, hanging kit included, and computer interface

    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.

    Great barracuda 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 are currently 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)
    Colored patterns

    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 optimal balance between 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.
    Light source

    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).
    Scalopping in aquarium

    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.
    necrosis bundled spot

    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.

    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 (patent pending) coated 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 coating on the light guide.

    Light guide

    Fig. 6

    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.

    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.

    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, implemented in the glass cover plate by using an abrasive blasting technique.
    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.


    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. 8)
    • The lightguide increases the source size, resulting in balanced caustic effects.

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

    Fig. 8 CoralCare product