Model Lab has a Light tab where you can add and modify physical lights on a model:

Within the Light tab, there are mainly 3 sections where you can further customize the light, but before that let's add lights to a selected mesh:

If you want to remove the light, just select the mesh where light is added, and click the Remove light button.

Light Color

These are three ways in which you can specify the color of the light:

• Material
  This will create the light color by using the material of the selected mesh.
• Temperature
  Select the Color Temperature of the light source ranging from 1500K to 7500K.
• Color
  RGB styled light customization also with HSV(Hue, Saturation, Value) sliders.

Brightness

This is where you can select a range of brightness of the light in lumens. It's separated into 4 brightness ranges:

• Weak light
  0lm - 250lm
• Light bulb
  250lm - 1500lm
• Ceiling light
  1500lm - 6000lm
• FloodLight
  6000lm - 100 000lm

The size of the mesh emitting light affects how intense the material is perceived, so larger light meshes will be perceived as darker compared to small light meshes.

IES profile

Model Lab lights support IES (Illuminating Engineering Society) profiles in further controlling how the light is being spread.
You can assign IES profiles by:

• Clicking into the IES preview for a few selections of profiles:
  
  
  
• Create and load IES profiles using other software:
  

You may also specify the direction of where the light spreads to.
This defaults in (0, 0, -1) in a normalized vector format, which means these values essentially range from -1 to 1 in defining a direction in its axis.
For example:

• X:1000, Y:1000, Z:1000 will be equivalent to X:1, Y:1, Z:1.
• X:2, Y:1, Z:0 will be equivalent to X:1, Y:0.5, Z:0

For example, a projector's light direction for this model would be: