While comparing various dive lights, you might have noticed that some lamps, especially video lamps, don’t have a flat, but a dome-shaped disk in front of their LEDs. This arched disk is also known as Domeport, but what are its functions?
In order to answer this question, we need to take a “quick dive” into the physics of light refraction.
According to the law of refraction, there is a correlation between the angles of incidence δ1 and the angle δ2 of the refracted ray:
n1 sin(δ1) = n2 sin (δ2)
n1 and n2 are refractive indices of the respective medium. The refraction index of air is close to 1. In the event of a transition from air to a different medium, the law of refraction can be simplified as follows:
sin (δAir) = nMedium sin (δMedium)
If we rearrange the equation to δMedium now, in order to find out what the angle of reflection is, we get the following equation:
δMedium = Arcsin ( sin (δAir) / nMedium )
Inserting the refractory index of water nMedium = nWater = 1,33 into the equation will result in the following correlation.
Things get interesting when it comes to the chart: As shown in the graph, it is impossible to exceed a certain value of the angle of refraction under water. No matter how skewed the angle is from which one illuminates the disc, a certain value can never be exceeded. This value is about 49°. Since we like to refer to full angles when it comes to dive lights, that value has to be doubled and therefore results in 98°.
One may ask himself now, why the refractory index of water is used in the equation instead of the refractory index of the material that the disk consists of. The reason for this is that although the light is broken according to those laws inside the disc, that refraction is shortened out of the equation as soon as the light ray leaves the disc in the direction of the water. Any errors resulting from that simplification are considered negligible.
Why does a videolight need a Domeport?
underwater cameras have a field of view which is broader than 98°.In order to completely illuminate such a field of view it is necessary to find a different solution. As you might have guessed, the answer to that problem is an arched disc: The so called Domeport.
I don’t film nor do I take photographs under water. Am I still in need of a Domeport?
A broad angle illumination light is useful, not only whilst filming and taking pictures. Being able to observe more of your surroundings during dives in caves or even wrecks greatly enhances the overall experience, due to an improved sense of spacial awareness.
Our SCALEO infinity has a special dome port. The unique shape allows not only for extreme broadangle photo- and video light, but also for a precise spotlight.The edge regions of the domeport are rounded down. A homogenous 120° video light with 600 lumen is generated in comination with a 60 watt LED cirle.The inner part of the dome port is flattened and allows for a precise spotlight with a 5° full angle and more than 42 000 Lux, above as well as below water.