Photofuckingmetrics.

Another bullshit lie that Revit MeP was sold on was its ability to perform lighting calculations.

After a half-dozen releases - it's still a bullshit lie.

There is now a 3rd party selling a plug-in that affords Revit some level of ability to do point-by-point photometrics (something that Visual has been able to do for over a decade - and for all means and purposes, is totally free).

I do not know how good it is (how
ever if it involves Revit chances are it is probably total shit).  As I pointed out before, Bentley systems chose to integrate Visual directly into its BIM software, allowing the user to design in Visual, and have the model populate the lighting fixtures automatically.

While using CAD it is necessary to import a background (and schematical lighting layout if desired) into Visual, export the finished product, and import it back into the drawing.  While this process can be a bit tedious at times, it is fairly simple - and highly effective.

The main reason for a point-by-point photometric plan is to show (with a fairly high degree of accuracy) what a proposed lighting design will look like when built.

For the mentally challenged, proper lighting is necessary to perform certain tasks, as well as for safety and security. 

The last two are key - because if someone gets injured or is the victim of some kind of crime, and they (or their lawyer) can show that insufficient lighting *may* be partially to blame, then lawsuits can ensue (watch for a future entry regarding another concept alien to Revit propagandists called 'liability').

For the unitiated, 'Visual Professional' is an industry standard program (or suite of programs for designing lighting of interiors, exteriors, sites, and roadways.  It is 'free' - at least to those who specify fixtures and have a working relationship with lighting factory reps.

It allows for quick and easy 3D modeling of buildings and/or spaces, insertion of light fixtures into this model (provided by nearly every single manufacturer in the form of IES files - which show the distribution pattern of the fixture, and the intensity of light), and will then display a grid of photometric values, and allow statistical analysis of specific areas as well as average, maximum/minimum light levels - and ratios of max/min.

While Revit can use an IES file - the process is painstaking, and only provides you with statistical information - which is useless without a visual representation (thus 'Visual').

An actual photometric allows field measurements to be taken and compared to the calculated values.  Visual also allows fixtures to be de-rated to take into account factors like lamp and lens degradation (commonly referred to as 'light loss factor' or 'LLF' to reproduce worst-case conditions when the lamp is near the end of its life, and the lens has become dirty.

Sometimes field measurements are purely for documentation purposes, but more often they are to show where installation errors (especially substution of sub-standard fixtures) cause complaints of improper lighting, and (mostly in the case of outdoor lighting) light trespass, glare, etc.

In short, this shit is important.