LED Decision ­‐ Making in a Nutshell

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# LED lighting contains no UV & little IR.
They are warm to the touch, in spite of some industries claim that they produce no heat. So consider carefully, how they might be used inside enclosures.

# To save most energy, insist on high luminous efficacy; 40 lumen/watt is a good starting point. Lower than that, cost savings will be marginal.

# To illuminate areas with more utilities (such as machinery, science exhibits, food services, hallways, educational activities, etc.); settle a color rendering index (CRI) above 80. For more attentive activities (such as viewing arts, ethnography, natural history collections exhibits, etc.); select LEDs with CRI above 90.

However, because CRI is an imperfect metric, it should be considered a target, not a firm criteria.

# If you wish to replace any conventional lamps (such as tungsten, halogen, or equivalent incandescent lighting) and still prefer to get “warmer“, select a color temperature between 2700K to 3500K. For preferences “whiter” or little “cooler“; pick 4000K ore more.

But generally, avoid higher color temperatures for light-sensitive materials, which common-used LEDs may have unacceptable peak at “blue” region in their spectrum.

# Be cautious of color temperature & CRI claims, because lamp-to-lamp consistency may not be adequate. Agree with vendor on your right to replace the lamps supplied, when consistency is inadequate out-of-the-box or a lamp changes color during operation.

# If possible, acquire & review LM-79 reports or any colorimetric-test results from the lamps’ manufacturer; looking for a positive (+)Duv specification which greater than +0.006 (exactly +0.0054). If the lamps may introduce a greenish appearance, perhaps it should be avoided.

# Once you have made a preliminary decision on several candidate-lamps, look at all of them by yourself:

o Checking color rendering on your own skin;
o Try for dimming it with recommended dimmers & specified transformers;
o Checking for flicker in undimmed & dimmed state;
o For LED-strips lighting, it should be dimmable to provide high level control in compact space. Dimming may extend the lamps’ lifetime, but the flicker could be a problem. Check this carefully!

# Most large brand-named lighting companies supply high-quality products, but they also supply poor ones. Make no assumptions of quality based on brand alone, because sometimes the smaller companies are motivated to provide a good support.

# Do not compromise too easily, if a given manufacturer does not have the right lamps based on your specifications or requirements (such as lumen, color, beam angle, or type of the lamps). There are many good products in marketplace that can cover a range of utilities and another manufacturer’s products may fit to your needs better.

# Retrofit lamps are easy to install in existing tracks or fixtures; but do not discount the lamps with a dedicated or unique design & shape. Some of these only require an adapter to fit an older track from their manufacturer.

# If you are going to be dimming your LEDs, confirm that the method is compatible to the used chips & drivers. No LED will change color upon dimming, when used the technique of pulse-width-modulation (PWM); but some of PWM techniques can introduce the flicker.

White phosphor LEDs may change color if the dimming is accomplished in same manner with as incandescent lighting – reducing the line voltage.

# Knowing what your product warranty covers!
A one-year warranty is common, but for longer periods of time coverage may be limited to a catastrophic-failure of the LED-chips. Failure of ballasts & drivers may not be covered at all.
Consider the return on investment payback (ROI) period!
You may be satisfied if ROI payback is less than the warranty period. Warranties exist that cover the major failures, significant loss of luminousity, and any visible change in color-temperature for up to 25,000 hours.

Source:

Druzik, James R., & Michalski, Stefan W. (2011), “Guidelines for Selecting Solid-­‐State Lighting for Museums”, Canadian Conservation Institute & The Getty Conservation Institute (with some edited).

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