I'm lighting a museum. What Luminus LEDs should be used?

High-energy photons, such as UV and blue light, have the potential to bleach and damage materials. This is particularly critical in applications where priceless historical objects, such as those in museums, are being illuminated. Cumulative photon damage can cause irreparable harm, and therefore, it is crucial to use non-damaging light sources to light these objects. However, when lighting these objects for public display, accurate color rendition is also necessary.

Three factors should be considered for these light sources:

1. Correlated Color Temperature (CCT): This is a measure of how warm or cool a white light source appears to human perception. It is defined as the black body temperature required to produce the same perceptual color coordinates as a real white light source. Although CCT is measured in Kelvin (K), high CCT (K) values are described as cool, and low CCT (K) values are described as warm. Several studies have been conducted on the psychological perception of paintings under different CCTs, and values between 2500 and 3500K are preferred.

2. Relative Damage Potential: This is a complex topic as different materials (paints, textiles, papers) have different damage responses to high-energy photons, and there is no consensus on an appropriate reference point. The actual calculation of relative damage potential is simple. It involves multiplying the spectral power distribution of the light source normalized to a common photometric power level by a damage weighting function and then normalizing it against a reference spectrum. In the table below, we have used 100 lumens, an unfiltered MR-16 QTH spectrum as the reference spectrum, and a mid-scale weighting function that has been adopted by CIE and ISO.

3. Color Rendering Index (CRI): The CRI measures how well a light source renders the true colors of an object. This is also a complicated topic with several different standards. In the table below, we use the general CRI (also called Ra), which is an average of the rendering quality for eight color samples. We also include the special red index, R9, which is commonly used as supplemental information to quickly judge the quality of a light source. An R9 value greater than 50 is considered acceptable, and one near 100 is considered excellent. The Ra value has a maximum of 100, which is commonly defined as an incandescent light source. These two numbers are simple and intuitive and are used in the table below. Luminus has data and reports for more complicated color quality measures, such as TM-30, for all of our white products, which are available upon request ([e-mail]).

The table below shows some Luminus LEDs that are suitable for museum lighting, compared to common light sources. Luminus white part numbers have a CCT-CRI code in them. For example, 27-90 is a nominal 2700K light source with a minimum Ra of 90.

Lamp & Filter	CCT (Test Article)	Relative Damage Potential	CRI	R9
D-65 (UV filtered sunlight)	6498K	2.24	100	100
AM1.5G (sunlight - not filtered)	5504K	2.12	99	96
D-50 (UV filtered sunlight)	5000K	1.66	99	99
F1 Fluorescent - UV filtered	6426K	1.63	76	-47
MR-16 - no filter (QTH)	3000K	1.00	100	99
MR-16 - UV Filter (QTH)	3000K	0.95	100	99
Incandescent Lamp - no filter	2866K	0.92	100	99
30-90 Perfect White	3099K	0.88	93	91
CLM-35-90 (Gen 4)	3411K	0.87	93	73
F4 Fluorescent - UV filtered	2939K	0.86	51	-111
CLM-30-90 (Gen 4)	3045K	0.84	92	64
CXM-30-95-TS31 (Smooth)	3026K	0.83	97	98
MP-3030-21C2-30-90 (Salud)	3097K	0.83	94	96
CLM-31-95 (Gen 4)	3157K	0.81	97	86
27-90 Sensus Gen 4	2646K	0.75	93	63

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