You want a nice, bright source that is cool enough not to damage film. I tried the (no longer available) Solux light, but although the color was accurate, it was too hot!
Most important is the QUALITY of the light, both for uniformity and for color reproduction. Color is not much of a concern with black-and-white negatives, but for color negatives (and slides), it is key. Diffusion needs to be completely uniform.
You want something with a very high CRI, or color rendering index. Especially important is good RED output that renders TCS09 accurately (see article linked below). Good candidates for this are usually LED light panels made for pro video and photography. If you use a variable color temperature source, you might want to experiment to find the color temperature that works best with the films you use.
There are 15 color test samples (TCS) used to evaluate CRI, and what you are looking for is light that renders as many of them accurately as possible. What is CRI? The ultimate guide to the Color Rendering Index | Waveform Lighting is a great read.
I use a Viltrox L-116t light panel. It has a reasonably good CRI of 95+, and decent red output. I am getting exposures of 1/250 at f/5.6 at ISO 200 on my Micro 4/3 camera with 30mm f/2.8 macro lens. Depth of field at that aperture is like f/11 on a 60mm lens on full frame… but on Micro 4/3, it is only two stops down from wide open, and right in the sweet spot of the lens where there is maximum resolution and good correction of lens flaws. 1/250 helps eliminate camera shake, but I use my mirrorless camera’s electronic shutter, turn off all camera noises, and use a two-second delay on the shutter to give the whole rig a chance to settle before the exposure.
I’m using an Essential Film Holder most of the time, along with a copy stand to hold the camera. Everything is leveled before a capture session. The EFH has a built-in diffuser that works perfectly. The bare light panel is not uniform, as you can see the individual LEDs behind its minimal diffuser, so the Perspex sheet in the EFH takes care of that.
Mask all stray light so only light from the negative enters the lens. Be sure the lens is scrupulously clean on all surfaces, too. These measures are to avoid flare.