The Navy has day signalling lamps for communication with pulses of light. The day signalling lamp used today has a halogen-type bulb as a light source, but there is interest in being able to use a light-emitting diode (LED) lamp instead. FMV together with an industrial partner have developed a prototype for a new light source based on this LED technology. FOI was given the assignment by FMV to perform optical verification measurements; after some reformulation and broadening of the assignment FOI has treated a few different areas that were considered important for the continued work in the development of the day signalling lamp. The contents of four important standards and conventions have been listed briefly. We review and explain the optical performance requirements for signal lamps in MSC.95(72) and describe how the optical verification measurements can be carried out in principle. Optical measurements have been performed by FOI to verify some of the requirements, but not all. The measurements show that the day signalling lamp with an incandescent bulb largely meets the tested requirements, but with some limitations. The day signalling lamp with an LED lamp has more difficulty meeting the same requirements, but this may also be because it was not easy to get the correct settings in the LED lamp mounting construction. A search on the internet shows that it is currently difficult to find commercial day signalling lamps for professional use that are based on LED technology, but that there are flashlights and searchlights that can in some cases be used for signalling. We describe the advantages and disadvantages of using LEDs as a light source from a technical point of view. We also suggest a couple of different development paths to produce an LED light source for the day signalling lamp. We briefly describe the connection between LED lamps and the problem of electromagnetic interference (EMI). Indicative EMI-measurements have been performed at FOI using the shortwave band 1-30 MHz on both LED lamps and incandescent lamps and it turns out that the LED lamp produces relatively little interference. The interference for low frequencies depends largely on the power supply and the cabling between the power supply and the day signalling lamp. This reminds us that EMI can occur in different places and that the entire system needs to be considered. The requirements set out in the standards (both in terms of optical properties and EMI) and how they should be verified are in many cases far-reaching and even though FOI has both the equipment and expertise, FOI is not an accredited measurement company. On a general level however, especially in the parts described in this report, FOI can be of support to FMV in the continued work within this area.