What’s in a light meter? How much do light meters vary? Are the tried and true really as true as we believe?

We decided to explore these questions by challenging our meters, old a new, to a performance test. We digitally controlled light levels in our illuminance testing facility and introduced light situations from powerful LED blow-out down to tightly sealed interior darkness. Lam Labs looked at traditional to contemporary illuminance measuring devices, including the Lumu smartphone plug-in meter and its app, the firm’s trusty standby (a Minolta T-10) and a chunky brown General Electric 214 model circa 1960. Lets see how they stacked up.

Findings

• Most results remain consistent, and their agreement indicates accuracy – however this was most true in illuminance levels from 0-20 footcandles. Results diverge and become increasingly disparate as the tested illuminance level rises.  

• The Lam Partner’s standby, the Minolta, T-10 ran largely parallel to the new, high-tech Lumu. New technology and trusted but older technology agree on light levels…proof that different generations can see eye to eye.

• The older GE 214 ran high for several tests, pulling the mean average up with it. If we ignore this model, there is a larger degree of consistency between all results.

Next Step

If we set the reliable Minolta-T10 as our baseline, how much do the others deviate from its results? The following graphs explain.

More Findings…

This graph shows each meter’s percentage of variance above or below the standard Minolta T-10 during each light situation.

The HS 1010 runs high consistently, with a 2-7% range for deviation. The Minolta TL-1 runs low consistently, with more variance – between 0 and 9% – and this range gives slightly more reason for distrust.

The Lulu is highly sensitive at lower light levels, suggesting perhaps it picks up light from the iphone screen to which it is attached – which of course can vary by setting for phone model. Alternatively, the Lumu may be finely tuned enough to sense tiny light leaks around doorways in the testing facility.

The GE 214 runs high overall, but reads significantly higher at increased light levels – not a typical trend and therefore this outlier can be tossed out of the runnings for accuracy.

Dr Meter also runs low, but with more uniform results than other meters, from around 2-6% variance, making it a reliable 2nd or 3rd choice after the Minolta T-10 and Lumu which have very similar performance.

The greatest variances – even larger than this graph would comfortably accommodate – are seen at lowest light levels. Those first few moments when a meter is exposed to light are unpredictable, indicating they all could use extra time for calibration and to reach peak performance, and multiple readings until consistent sequential readings are reached.

THE  LIGHT METER ACCURACY AWARD GOES TO:

1st    Minolta T-10 & Lumu

2nd     Dr. Meter

3rd      HS101

4th      Minolta TL-1

5th    GE 214

This study was performed by Brittany Lynch and Piper Ainsley in September 2016.