ILLUMINANCE METERS

  From time to time most lighting engineers will need an illuminance meter. But unlike photographic meters, illuminance meters are few and far between. One cannot merely walk into a local store and view or purchase these lighting marvels. There is no such thing as “try it before you buy it.” At least this was my dilemma in searching for the appropriate meter. About the best one can do is call each individual manufacturer and request literature. Even this is the equivalent of reading a brochure about the latest Porsche or Ferrari and making a decision about which one to buy. Hopefully, this article will shed some light for those contemplating the purchase of a luminance meter.

With the help of five of the leading manufacturers - The Cooke Corporation, Graseby Optronics, International light, Inc., Minolta Corporation, and Yokogawa Corporation of America - I am able to provide some insight for the engineer seeking a more in-depth look.

I would categorize out test luminance meters into three separate groups: (1) basic, low cost, straightforward light measurement; (2) multi-featured, moderate technology metering; and (3) state-of-the-art, precise, laboratory standards measurement.

Our first group of meters consists of the Cal-Light 400 by the Cooke Corporation, the Minolta TL-1, and the Yokogawa 510-01. These are lightweight (5-10 oz.), have liquid crystal displays, a calibration matching the CIE Standard of better than + 3 percent, and priced below $500. This no-frills equipment gives general illumination evaluation and is cosine corrected, with sensitivity of 0.1 - 400,000 fc.

Our second group includes the Minolta T-1 and the Yokogawa 510-02. These meters weigh approximately 10 oz. have liquid crystal displays, and calibration matching the CIE Standard of better than + 2 percent, and priced from $745 for the Minolta to $999 for the Yokogawa. Both have slow and fast response settings with a measuring range of 0.001-999,000 fc, luminance deviation capabilities, and manual or automatic ranging. In addition, Yokogawa has three multiple outlets: recorder output, digital output, and comparator output: a color correction factor setting function: a ripple measurement function: and best of all, a timer-hold function so you can step away and it ill take a reading at a prescribed tine from 1 to 99 seconds.

The third group includes the Graseby model 371 and International Light's IL 1400A. These meters provide performance specifications unmatched by any other hand-held luminance meters on the market. Both companies have an accurate, versatile light meter that would definitely meet the demands of even the most highly technical engineer. These are truly bringing the sophisticated laboratories into the field by means if their portability. Once the information is gathered, it can be downloaded to the main terminals. But technology does not come cheap: the Graseby is $750 for the base meter and about $500 for the appropriate sensor head. The International Light is $720 for the base meter and about $600 for the appropriate sensor head.

It's time for the pros and cons. The old adage, “You get what you pay for” is highly applicable. The first group is basic, straightforward and relatively inexpensive. If one has minimal measuring requirements, these meters will suffice.

The second group bumps the price up but adds more features: probably the best choice for most engineers who are budget conscious but need some versatility. This would be my choice for the moderate company willing to spend a few more dollars for a good all-around meter.

The third group is beyond a doubt the “Rolls Royce” of illuminance meters. But, because of cost and highly technical nature, some companies would consider this overkill. Although the less expensive meters are about the size of a television remote control, these two are almost three times in size and weight.

After a through examination of the above metering systems, I must place the Yokogawa 510-02 at the top of the user-friendly category. Its size and ease of operation make it a quick “grab-and-go” meter. Although it doesn't have the capabilities of the Graseby or International Light, nearly anyone would be able to use it without spending hours studying an instruction booklet. I believe this unit will satisfy 90 percent of most lighting engineering needs.