Reply To: UV/Visible light meter

Les Kacev

Scott Rosenfeld is correct. The Elsec 765 is an excellent choice and is widely used by museums.

I would urge all working in the lighting field to ensure they have a good understanding of what their objectives are before determining what meter or datalogger to buy or recommend. A few general comments may help.

1. Broad range products are seldom accurate. I would suggest separate devices for UV, VIS and IR measurements.

2. With the coming of age of solid state lighting [LED] lighting, it is critical that museums have the ability to define what they are looking for and then determine if the lights they consider for purchase meet their specs. One simply cannot rely on manufacturers’ recommendations or specs. Too many institutions unknowingly purchase unsuitable products because their objectives are not defined and because of reliance upon salesmen or even scientists who pose as “experts” but who really are not LED specialists. I urge all to read Druzik and Michalski’s article on museum lighting.

3. There are many characteristics to consider in selecting LED lighting. I will mention just a few. Spectrum, location relative to the Planckian locus in one of the CIE chromaticity diagrams, correlated color temperature [CCT], color rendering index [enhanced CRI from R1 through R15], purity and many more. To measure these one needs a spectrometer. Today one can purchase a hand held spectrometer like the Lighting Passport for under $2000 which can measure all the critical parameters you need to make a rational decision.

4. It is important to understand that all filter based meters and tristimulus meters use VLamda as a basis. VLamda was determined by the CIE in 1924 and is no longer accurate for measuring light and especially LED lamps and luminaires. It is lacking in the blue/green and the red range.

5. Understanding 1 to 4 above makes the choice of a datalogger for continuous measurement a science rather than an art. In general, spectrometer based units are much more accurate than filter based units, but they are also more expensive.

Education is the key to implementing and monitoring museum lighting.