Yes, any light source can be a possible source of interference. The level of interference however strongly depends on the type and brightness of the light source. Typically, constant light sources (such as sunlight, incandescent lights) cause much less (if any) interference than pulsed light sources (dimmed LEDs, fluorescent tubes with an electronic ballast).

We have worked diligently to achieve the widest possible dynamic range with our optical modems, making them as tolerant as possible to ambient light conditions. While some competing products may only work at depths of 150 meters and below in near darkness, our modems are typically more tolerant to the ambient light. LUMA X UV is the best choice in the environment with a lot of ambient light pollution.

The human eye adapts to light on an exponential scale, making differences in light levels less obvious to us. However, for a photosensor like the modem's receiver, even small variations in light can have a significant impact. The best performance for the LUMA modems is achieved at light levels of 1 lux and below, which is quite dark. For comparison, a well-lit office or a trade show floor can have light levels around 500 lux, while direct sunlight can reach up to 40,000 lux, which is approximately 1 million times stronger than the modem's signal. Deploying LUMA modems under direct sunlight, for testing or for data transfer, is not recommended.

For one-way communication, such as a camera streaming video via UDP, it can help to position the receiving modem looking down and the transmitting modem looking up. This arrangement reduces the receiving side's exposure to sun and sky. Additionally, placing a plate behind the receiving modem can create a "shadow zone" to further reduce back-scattered sunlight around the modem.

In shallow water with sunlight, we recommend using LUMA X UV, specifically designed for more challenging ambient light conditions as it operates in the UV spectrum. However, while LUMA X UV is robust against visible artificial light sources like halogen and LED lights, natural sunlight still contains a significant amount of UV light. Adding a sunshield to keep the modem receiver in shadow as much as possible would measurably improve the performance. This can be achieved by mounting a larger plate above the modem to block the sky's view or by placing a tube around the LUMA modem, extending it 5-10 cm beyond the front lens. Depending on conditions such as depth, turbidity, and light scattering, this can extend the effective communication range of the modem.

The maximum range (and speed) specified in the data sheets of all LUMA modems does assume clear water, as it is typically encountered in deeper waters. Turbidity does decrease the maximum range at which LUMA modems can operate. In turbid waters the maximum communication range for LUMA X and LUMA 500ER is about 3 times the visibility ("Secchi Depth"). A more detailed analysis for LUMA X is available upon request.

No, all LUMA devices are transceivers and can send and receive data (half-duplex).

No, LUMA modems can typically not communicate between each other as typically one of the following differs between two different models: wavelength, speed, modulation, transmission range (sensitivity).

A number of configurable forward error correction schemes, which increase the reliability of the communication channel, are implemented. Faulty packages are automatically rejected on the receiving side using a checksum which is automatically added on the sending side. In order to maximize the transparency and versatility of the LUMA optical communication nodes, no additional protocol layers (such as TCP) which would ensure data delivery through resending, are implemented.

LUMA modems do not have a communication protocol "per se" like acoustic modems do, as they act as a transparent link replacement for a serial cable (LUMA 100/250LP/500ER) or an Ethernet cable (LUMA X/X-UV). More specifically LUMA X modems act as a transparent link to end devices, similar to a network switch or a wifi router. The LUMA X modem works in the link layer of the IP stack, which means it will forward any Ethernet packet that it sees without the need for an additional protocol. LUMA 100/250LP/500ER modems act like a wireless serial cable. While the modem internally packetizes the continuous serial stream adds a checksum, possibly does forward error correction, do the devices on both ends it looks like the continuous serial stream from a cable. There is however an API for LUMA X/X-UV which allows the user to obtain modem status information and to set parameters. This API is documented in the manual for the LUMA X/X-UV modem.

All LUMA modems provide a fully transparent connection so the devices on both ends are usually not even aware of the modems in between them. So like an Ethernet cable or a serial cable the modems are agnostic to the data sent across them and the operating system of the hosts. LUMA X and LUMA X-UV do have two ways to interface them while they are in operation: 1.) a REST-based API through which you can configure the modem and obtain modem and channel information 2.) a web interface running on a web server inside them modem through which you can configure the modem and obtain modem and channel information The API and web interface are documented in the LUMA X/X-UV manual which can be obtained on our web site. This documentation also contains Python examples for API access.

Not necessarily. While the maximum range indicated in the data sheet requires a direct line of sight, indirect light from reflective surfaces or scattered light from particles in the water will often allow for a communication link even without line-of-sight.

All LUMA modems come with a Subconn connector which is suitable for underwater operations. However in order to test the modems on the bench or prepare them for deployment we developed adapter boxes for all of our modems which convert the Subconn connector to 1.) a standard barrel plug-style power connector and 2.) a micro-USB connector (with built-in USB to serial conversion) for our LUMA 100/250/500 modems or an RJ45 connector for our LUMA X and LUMA X-UV. We strongly recommend everyone buying their first LUMA modems to get these power/data cables along with the modems.

You do not HAVE to buy the power plugs and power/data adapters from Hydromea, but we STRONGLY suggest it. Customer problems while setting up LUMA modems can often be traced back to connectivity issues, so the cables we sell provide a base-line test and development functionality which is very useful when setting up and integrating LUMA modems into your system. They also provide a reliable connection to a PC for firmware updates. We thus recommend every first-time buyer to get a pair of power/data cables along with the power supplies.

To fully demonstrate the modem's capabilities, it's best to conduct tests in clear water at depths greater than 30 meters, during the evening or night, or indoors with lights off to minimize sunlight exposure. Turbidity in the water can also affect the expected range, with LUMA modems using blue light typically achieving about three times the visibility range in dark conditions compared to twice the range for LUMA X UV. In the environments with some ambient light present, LUMA X UV would work best as it operates in the invisible UV spectrum and is typically not disturbed by the visible light sources such as halogen and LED lights.

With the release of firmware V1.4, LUMA X as well as LUMA X-UV modems automatically adapt the emitter power (number of transmitting LEDs), the receiver sensitivity and the transmission speed depending to the signal-to-noise ratio (SNR) encountered. This feature can be disabled, allowing for a manual setting of transmitter power, receiver gain and transmission speed. For other LUMA models this feature can be implemented, contact us for further information.