Out of the Wood | Total lumens—revisited Where F is the value from Table 1 based on our estimate of center to edge ratio. If you don’t know that, then use F=0.4 as an average. No, it’s not precise. Yes, it could be widely out if the luminaire has a really unusual distribution. Yes, the manufacturer may disagree, but they should also give you the full information so you don’t need to do this! However, if you don’t have the full data, this approximation is going to give you at least a ballpark answer. It’s also simple enough that you can often work it out quickly in your head. “ Forget the rhetoric. The truth is in the numbers . . . Once we have an estimate for total lumens we can get to our true goal of trying to evaluate if a luminaire is energy effi cient, and use it to work out the effi cacy of our luminaire. If our example luminaire shown in Figure 2 consumed 300 W from the supply, then we can now estimate that it has an effi cacy of 4500/300 = 15 lm/W. The result isn’t an exact answer and by no means is a replacement for full data that includes true measurement of total lumens. However, if nothing else, doing this simple math might give you a feel for how total lumens are affected by the beam profile, and which luminaire really delivers energy savings. Mike Wood runs Mike Wood Consulting LLC which provides consulting support to companies within the entertainment industry on product design, technology strategy, R&D, standards, and Intellectual Property. A 30-year veteran of the entertainment technology industry, Mike is the current chair of the PLASA Governing Body and Treasurer of PLASA North American Regional Board. Mike can be reached at mike@mikewoodconsulting.com. “ FALL 2011 25 PROTOCOL