FAQ - Benchmark scoring method (the stars)

We have attempted to rate the lights we have tested with a 5 star rating, in a relatively subjective manner, based solely on the specifications of the light. This reprsents our opinion on what is important from a technical point of view.


Step 1: Give points to each light based on certain metrics (see below).

Step 2: Total up the points to get an overall score.

Step 3: Take the range of scores across all the lights tested and divide the range into 8 ranges.

Step 4: Assign a star value (1 to 5) to each light depending on which range it falls into, including half stars.


Metric Description Formula
Lumens Total light output of the globe. At the moment LEDs lights are often dull but rarely too bright. So we consider more Lumens to be a good thing. The denominator of 50 was chosen somewhat arbitrarily. A standard 60W incandescent globe outputs around 800 lumens, which would give 16 points. Lumens / 50
Watts Electrical power used. Which also directly relates to the ongoing running costs. So less Watts is a good thing. At least until very low wattage are reached. A drop from 50W to 25W is a substantial gain, but a drop from 3W to 2W is of much less interest. log(100/(max(Watts,3),10) * 10
Purchase price Everyone likes a bargain. 5 * log (100 / Price)
Estimated life The longer the life time of a bulb the better. We don't give this too much weight becuase we don't believe all the claimed figures. Plus we don't think the difference between 10, 20 and 30 years life is significant. In 15 years LED lights will be far better and you'll want to replace them even if the old ones still work. min (Lifetime Hours, 50000) / 5000
CRI The color rendering index. It is the ability of a light to illuminate objects and make the colors look natural. Higher values are generally better, but the CRI measurement is somewhat controversial and not accurate in all circumstances. We assume values below 60 (or having no specified value available) are equally bad. (max (CRI,60) - 60) / 5
PF The power factor. A high power factor is a good thing. Power factor values are always between 0.0 and 1.0. PF * 5
Running Temperature The running temperature of the globe at 25°C ambient air temperature. Low temperatures will allow the globe to last longer and also produce higher output after their warm up period. In our opinion there is no great benefit to going below 50°C. 90 - (min(max(50,Temp),90)) / 4
Dimmable How well the light dims compared to hypothetical perfect linear dimming. No points are given for globes that don't dim at all. Dim rating / 2
Warranty period How long the warranty period is. For LED lights which appear to have no stated warranty we assume they have 6 months. We cap this a 7 years, as we are dubious that any company would honnor warranties that far in the future. min(max(Years,0.5),7) * 2
Flicker How stable the light output is under nominal conditions. Measured with a compatible transformer, if required, but without a dimmer. Lower values for Flicker Percent and Flicker Index are better. Typical values are 0% to 100% for Flicker Percent and 0.0 to 0.5 for flicker index. 6 - ((FlickerPercent + (FlickerIndex * 200) ) / 25
Difference in claimed and measured performance How misleading the claimed wattage and lumens are compared to their measured performance. Points are deducted if the total percentage difference of claimed lumens to measured lumens and claimed wattage to measured wattage is more than 10%. - floor((abs(claimedLumens-measuredLumens)/claimedLumens + abs(claimedWatts-measuredWatts)/claimedWatts)*10)*2
Reviewer manual adjustment Normally not used. Will be used for exceptional cases where the light completely fails. +-10


Example calculation

Here is an example for a LG Electronics LED globe.

Lumens: 9.64
Watts: 11.08
Price: 3.72
Hours (life): 6
CRI: 4.4
Power Factor: 5
Temperature: 5.2
Dimmable: 0
Warranty: 6
Flicker: 3.6
Overall Score: 54.69





Related Pages


Back to FAQ index