Laser Energy Transmitters (or LETs) are the backbone of your power delivery network, they can send power over a distance of up to 64m and can deliver it directly to machines, power storage blocks, or another LET to extend the range.
To open the control panel for the LET press the 'Interact' key (default 'E'). This allows you to upgrade the lens which will boost power transfer. You can also switch the firing mode so that it will wait for a full battery before sending power. LETs have a small internal capacity, consider complementing them with Power Storage Blocks to ensure a reliable supply of power as supply and demand vary.