Beginning with September 2017 production, Lexus changed the cargo area lights from incandescent bulbs to LED modules. Unfortunately, the LEDs they
selected are so dim as to be practically useless, with each module (one on each side) containing just a single LED chip operating at 30 milliAmps (0.09 Watt). You cannot just swap a brighter bulb unless you purchase the pre-2018 lamp assemblies.

This relatively-easy modification replaces the dim factory LED modules with an array ("panel") of LEDs operating at a combined power of 1 Watt, for approximately 10 times the light output.

The first images below show the factory LED module and the cargo area illuminated with the factory lamp on the left side and modified lamp on the right.

WHAT YOU WILL NEED:
(1) LED arrays - purchased from Amazon
(2) Nylon trim removal tool
(3) Electrical sealant putty (available in the electrical department at Lowe's or Home Depot). This is commonly used to seal openings where wires enter a
building. It remains pliable even at low temperatures, and is easy to completely remove when warm.
(3a) (not shown) Metal putty knife, width 3/4" to 2".
(3b) (not shown) Portable hair dryer.
(3c) (not shown) Medium and small flat blade screwdrivers.

REMOVE THE CARGO LIGHT ASSEMBLIES
Look at the light assemblies while turned on. The left side of both should be noticeably darker than the right, because that is where the connector is located. The assembly must be pried out from the edge opposite the connector (usually the right edge).
(4) If interior temperature of the vehicle is less than 75F, warm the lamp assembly with a hair dryer, set on Low, to make the plastic less brittle.

Assuming the darker region is to the left, push the putty knife into the lower right corner to create a small gap between the light assembly and the interior trim panel. I first applied duct tape to the panel surrounding the lens to protect it, but this precaution is not essential.
(5) Insert the trim removal tool into the gap and work up and down to gradually pry out the right edge of the lamp assembly.
(6) Next, slide the assembly to the right and withdraw it completely. Use a small screwdriver to push the release tab at the rear of the connector (vehicle end), and separate it from the lamp assembly.
(7) To separate the LED module from the lens, first warm the parts with the hair dryer, then slide a medium size screwdriver under the LED module to push it
upward while using the small screwdriver to pry the clear plastic retainer clips on each side outward.

REPLACE THE FACTORY LED MODULE
(8) Lens with OEM LED module removed, and new LED panel beside it.
(9) Flip over the LED panel and center it between top and bottom of the lens. The wires and connector should be located at the end with the retainer clips.
(10) Use 3 dollups of putty to adhere the LED panel to the lens. Press them into place with your fingers. You will not need a lot.
(11) Plug the LED panel connector into the factory receptacle. The blades should plug into the rectangular openings (red arrows in image). If the panel does not immediately turn on, reverse the connection.
(12) Use a generous dollop of putty to embed the connector and plug into the space between the retainer clips. The putty also prevents the connectors from separating under vibration. An ordinary plastic twist-tie can also be used to ensure the plug and receptacle do not separate over time.

Fold up the harness and slide the connector-end of the assembly into the left side of the cargo area opening, and then press on the right end to snap it into place.

I saved the factory modules in a plastic bag storeed under the cargo floor, in case I ever wanted to revert back to OEM.