7 Tips for Buying High-Quality LEDs

With LED light fixtures becoming the norm on any new construction and gut reno projects, it’s worth understanding what you get with your fixture package. Unlike incandescent light, not all LED fixtures are born equal. There are quite a few considerations when specifying LED fixtures, from the dimming range and technology to variations in color and temperature and even the lifetime of the fixture. Below are seven aspects to consider when specifying LED fixtures for your project or your house.

1. Compatibility with dimmers

It’s a common misconception that any LED dimmer can be paired with any dimmable LED light bulb. Unfortunately, that is not the case. All LED fixtures come with a Driver. The driver technology determines whether the LED can be dimmed and how, as there are several dimming technologies on the market. Some examples are Forward Phase, Reverse Phase (also known as Phase Control or Triac), Electronic Low Voltage (ELV), Magnetic Low Voltage (MLV), and 0-10V which requires special wiring.

Most LEDs have multiple driver options, so it’s important to check if the selected dimmer can support the driver that was specified with the LED fixture.

The easiest way to ensure that your light bulbs and dimmer controls are compatible is to check the lamp’s manufacturer spec sheet or dimmer compatibility sheet.

These are the main LED Driver technologies

Triac (forward phase) dimming uses “standard” wall dimmers that are widely used in installations across America.

• 120V only
• Low End adjustment on dimmer may be necessary to achieve optimal performance.
• Dims down to as low as 1% in current and light output with select dimmers.
• Generally dims down to 5% light output.
• Consult the dimming manufacturer for installation and programming instructions.
• Must meet dimmer minimum load requirements per dimming manufacturers.

ELV – Electronic Low Voltage (reverse phase) dimming uses specialized “ELV” dimmers.

• 120V only
• Low End adjustment on dimmer may be necessary to achieve optimal performance.
• Dims down to as low as 1% in current and light output on select dimmers.
• Generally dims down to 5% light output.
• Consult the dimming manufacturer for installation and programming instructions.
• Must meet dimmer minimum load requirements per dimming manufacturers

0-10V Dimming Driver Option

0-10V Dimmers have been used in commercial applications for fluorescent lighting and occupancy and daylight sensor systems for years and are now becoming popular with LED products. One reason this standard is widely established is that it is defined in the IEC standard number 60929 Annex E, making it acceptable to most engineers

2. Dimming capacity:

The human eye responds to low light levels by enlarging the pupil, allowing more light to enter the eye. This response results in a difference between measured and perceived light levels. A lamp that is dimmed to 10% of its maximum measured light output is perceived as being dimmed to only 32%. Likewise, a lamp dimmed to 1% is perceived to be at 10%.

How important is this?

By enlarging the pupil, the human eye responds to low light levels and that allows it to see more light. For example: if the measured light output is 1%, then the perceived light level will be 10%. For the brightness of the luminaire to be matched to our eyes, the dimming curve has to be configured appropriately. If not, the perceived changes in brightness will be affected.

A good LED driver with the capacity to dim to 0.1% configuration provides the option to set the dimming behavior as per the human eye functionality and application preference. So, if you want a 50% reduction in the light intensity, you need to select the expected dimming response. Therefore, when shopping for LEDs, don’t be fooled: an LED which can dim to a seemingly low 5%, will be perceived by the human eye at more than 20% which is rather bright.

3. Color difference:

For white LED lights, color consistency can be a critical but often overlooked quality that can make or break a project. Read on to learn how and why color variation exists, and how to ensure you can attain excellent color consistency for your LED light project.

What exactly is color consistency?

In general, color differences can be characterized across two axes – blue/yellow and green/magenta. For example, you may find that one light is “bluer” than the other, or more “green” than the other.

The blue/yellow difference can be characterized using color temperature (in degrees Kelvin). Acceptable color variation depends on the application, but for warm white, +/-75K is typically the threshold of noticeable color difference, and +/-150K for normal white or cool white.

Green/magenta variation can be described using a lesser known metric called Duv. A Duv of 0.000 indicates a light source that is neutral. A negative Duv indicates a magenta color shift, while a positive Duv indicates a green color shift. Typically Duv values that differ by more than 0.002 are noticeable.

Keep in mind that Duv variation is very much overlooked as a metric but is arguably more noticeable than Correlated Color Temperature (CCT) variation. If color consistency is critical for your application, be sure to ask your supplier for Duv tolerance metrics.

Standard Deviation Color Matching (SDCM) or MacAdam Ellipses

Some sophisticated manufacturers will describe their color consistency using a metric called SDCM or MacAdam ellipses, both of which refer to the same concept and metric. The unit of measure is a “step” and the larger the number of steps, the larger the variation in color.

In general, color consistency is deemed acceptable when it is within a 3-step SDCM range for standard applications, and 2-step SDCM range for more demanding applications for professional or architectural uses. In some cases, even narrower color tolerances are needed, but most people will not be able to tell that there is any color deviation once consistency reaches 1 or 2 SDCM.

SDCM is a superior metric compared to CCT and Duv for two reasons. First, it captures the variation in both the blue/yellow direction and green/magenta direction and distills it into a single number. This can be useful because in some cases the color inconsistency can occur in both dimensions. The second reason is that a 100K color difference is considered larger at lower color temperatures. SDCM algorithmically takes this into account and makes the necessary adjustments depending on the color temperature. The primary disadvantage is that many manufacturers are not sufficiently concerned about color difference and will oftentimes be unfamiliar with this metric.

It’s worth noting that LED fixtures degrade over time and thus the SDCM or MacAdam ellipse, may shift over time. A good quality LED fixture should maintain its SDCM values for the duration of the manufacturer’s advertised fixture lifetime and/or warranty.

Why do LED lights get dimmer over time?

The term degradation in relation to LEDs refers to the decrease in luminous power over the course of the LED’s life.

Degradation is like an aging process in which the LED becomes dimmer and darker over its life cycle as the LED driver generates heat and the heat causes the LED fixture to degrade over time. In the US, LEDs are often given an L70 rating. This rating describes the time it takes for lumen output to drop below 70%. Although other ratings like L50, L80 and L90 can also be used, L70 is the most common as this is when the brightness of the light becomes markedly different. Once the LED lumen output has dropped below 70%, it will still emit light, but it may no longer be fit for purpose. Different environmental conditions such as excess heat in the space where the fixtures are installed, can cause degradation to accelerate. In addition, lumen degradation is not a linear measure. Degradation may start slowly, but then accelerate after it drops below the 70% threshold.

4. Color temperature:

The temperature of light is measured in degrees Kelvin which is what the K at the end of the light temperature value represents. Most LEDs are locked to one color temperature, i.e., 2700K, 3000K etc. When dimming these LEDs the light tends to become grayish, while incandescent or heat based light (like the sun) is cool when bright, i.e., 4000K or higher and warm when dimmed, i.e., 1400-1800K.

LED Lighting and Color Temperature

In technical terms, color temperature is the temperature of an “ideal black-body radiator that radiates light of comparable hue to that light source.”

Let’s try that in English: imagine an object made of iron. At room temperature, the object would obviously appear black. Heated up to 1500 degrees Kelvin (K) however, it would glow red. At 2700K, it takes on a warm, yellowish glow. At 4200K it appears bright white, and by 5500K it glows blueish. That’s how the color temperature numbers are determined.

Enough of the geek-speak, just remember that the number indicates the general look or feel of a light or the light bulb colors when it’s turned on.

Here’s a color temperature cheat sheet to use when shopping for LED lighting:

5. Uniformity

Color consistency is defined using MacAdam Ellipses. A one step MacAdam Ellipse defines an area of a chromaticity diagram where the average person is only able to distinguish a single color. The diagram shows examples of one step ellipses on a chromaticity diagram where only a single color can be distinguished by the average observer. Note that the human eye is more sensitive to wavelength changes in the blue and red spectrums than green, hence the differing size of the ellipse between these colors.

When blending different types of LED applications such as cans, strips/linears, and decoratives in one space it’s hard to keep color and temperature consistent.

In a single production batch of LEDs the majority will typically fall within a five step MacAdam Ellipse with a small proportion falling outside this with greater color variation. If LED manufacturers were to discard LEDs outside of a one step Macadam Ellipse to give perfect color consistency it would mean the majority of LEDs would be wasted making production costs prohibitive. Instead, LEDs are measured on the production lines to determine their color and then batched together into color bins so that luminaire manufacturers can select those most suitable for their products. The wider the color bin that a luminaire manufacturer is willing to accept, the lower their cost becomes as the LED manufacturer is able to sell a greater proportion of the yield from each production run. The lowest cost color selection is typically “Full Yield”, in which the luminaire manufacturer purchases the entire production run of LEDs regardless of variations in color. Although this reduces cost it inevitably results in a color variation between luminaires, and between chips within a single luminaire, that most clients would be unwilling to accept. At the other end of the cost spectrum a luminaire manufacturer can order one step MacAdam Ellipse color bins, however, such a narrow and expensive color selection would be unnecessary in the vast majority of applications.

6. CRI VS. TM-30:

What is CRI?

Developed well over 50 years ago, Color Rendering Index (CRI) measures the ability of a light source to reveal the colors of various objects in comparison to the ideal (daylight) source. In other words, how similar an electronic light source (like an LED luminaire) renders colors compared to natural light.

CRI indexes eight standard colors and how these are represented by a specific light source compared to natural daylight. 100 is the optimal ‘best’ score. The average CRI for modern LED lighting is between 80 – 90, and are considered a “good” color representation, relatively true to nature. However, best in class LEDs will have a CRI of over 90 and will render the colors of the interiors you are designing more effectively.

Why a New Metric?

Well, since around 1974 the method for measuring color rendering has been largely unchanged – unlike the advancement of lighting and technology. With LED lighting so common now, lighting designers and scientists strongly feel CRI is becoming less effective at achieving desired results in the real world. While many lighting professionals will continue to work with CRI, TM-30, developed in 2015 by the Illumination Engineering Society (IES), provides an alternative, more comprehensive color index.

What’s the Difference Between CRI and TM-30?

• Only eight color samples are tested for CRI.
• CRI only uses color fidelity to base its index score, ignoring other spectral values.
• When comparing CRI values, Correlated Color Temperature (CCT) must be identical.
• Two separate light sources with the same CRI score can render colors very differently.
• A high CRI measured rating could produce or represent a low TM-30 score.

CRI measures just 8 color samples. TM-30 uses 99 color samples – quite a difference! The use of 99 color samples versus just eight allows for a more statistically representative and reliable metric.

CRI is measured using a light fidelity metric ONLY. The TM-30 rendering index uses a more comprehensive range of three color metrics:

• Color Fidelity (Rf – “same-ness” index)
• Color Gamut (Rg – saturation index)
• Gamut Shape (visual description on hue and saturation)

Color Fidelity: Enumerates the accuracy with which the color appearance of surfaces and objects under a given test source match their appearance under a reference illuminant.

Color Gamut: Enumerates the average increase or decrease of the chroma of surfaces and objects when viewed under a given test source relative to when viewed under a reference illuminant. As an example, an Rg value below 100 indicates that, on average, the light source renders colors as less saturated than the reference source, and an Rg value above 100 indicates that, on average, the light source renders colors as more saturated than the reference source.

Color Vector Graphic: Provides a visual representation of hue and saturation changes occurring in surfaces and objects when viewed under a given test source relative to when viewed under a reference illuminant. The addition of the Color Vector Graphic provides a wealth of color rendering information beyond averages, showing us at a glance exactly where the hue and saturation shifts are taking place on the color spectrum

7. R9

What is R9?

R9 is the score that represents how accurately a light source will reproduce strong red colors. “Accurate” is defined as similarity to daylight or incandescent bulbs, depending on the color temperature. Just like each of the CRI R value calculations, R9 is determined by calculating the reflected color from a theoretical object with the reflectance profile defined as TCS9. The reflectance spectra is provided below:

What is notable is that the TCS9 spectrum is almost entirely composed of red light. Spectrum-wise, we see this as wavelengths longer than 600 nm. This means that if there is not enough red light in the light source, it will make red colors appear “off” or different.Below is a typical LED spectrum compared to the reference source (daylight). There is a very notable lack of red light emitted by the LED at wavelengths past 600 nm.As a result, the R9 value for this LED is at -1.4. (That’s right, a negative number!) This is in spite of the fact that the general CRI (Ra) comes in at 79.

Why is R9 important?

R9 is a very important metric because it represents how well an LED renders the red color and if we base our LED selection purely on CRI values, many light sources might be lacking in red content, but this fact will be hidden due to the averaging out of CRI calculations which do not include R9.As the chart below shows, a light source can actually perform quite well with the first 8 test color samples, scoring quite well for R1-R8. For the general CRI Ra metric, this means that an LED with poor red color rendering can still get by with an 80 CRI (Ra) rating.

What is a good R9 value?

Although the maximum possible value of R9 is also 100, unlike average CRI numbers, R9 should be judged a bit differently. Mathematically, R9 is far more difficult to achieve a high score compared to the other R values that comprise the CRI calculations, and is far more sensitive to spectral variations. Therefore, an R9 score of 50 or above would be considered “good” while an R9 score of 90 or above would be considered “excellent”.You will therefore find that most lighting products available in the market will rarely specify the R9 value, and when they do, rarely will they guarantee anything higher than 50. Even at Waveform Lighting, we specify R9 > 80 or R9 > 90, and are unable to guarantee anything higher than R9 > 95 due to this sensitivity. This is due to the fact that CRI utilizes the CIE 1960 uv color space, which is skewed in a way that exaggerates color differences in the red region of the chromaticity diagram. Since CRI is a calculation that quantifies color differences between a light source and a reference source, a larger calculated color difference will result in a larger decrease in the R score.

Why is red such an important color?

Red is a crucial color for many applications including photography, textiles and reproduction of human skin tones.Many objects that do not appear red actually are a combination of colors, including red. Skin tones, for example, are very much influenced by the redness of the blood that flows right beneath our skin.

Therefore, a light that lacks red will make a person look pale, or even green. This can be problematic for medical applications where color appearance is critical for accurate diagnoses. In other applications such as photography, aesthetic appearance is crucial and many times cannot be corrected for even in post production and digital editing.

When searching for a high color quality LED, be sure to inquire about the CRI as well as its R9 value.

Conclusion

As you can tell, there are many considerations when choosing LEDs for your space. Sometimes it’s hard to extract all the necessary specifications, especially when ordering LEDs online or from low-value sources. Many low-cost manufactures tend to hide the important specifications such as the MacAdam Ellipse or R9 values. In addition, many lower-cost LEDs don’t dim sufficiently to achieve the required perceived results vs. the actual result. And finally, most LEDs lack the ability to adjust the temperature of the light (degrees Kelvin) and are locked to only one temperature setting, resulting in grayish looking light when dimmed.

Fortunately, there is a brand of LEDs that doesn’t require any dimmers (yes, you heard it right) – so compatibility is not an issue. Dims to 0.1%. Rated to one-step MacAdam. Has a CRI value greater than 90 and R9 value over 50, and adjustable temperature between 1400K and 10,000K while maintaining uniformity across all various form factors such as recessed lights, track lights, bulbs and linear (tape) lights. It also has over 16 million color combinations and can mimic natural daylight. Want to know more? Call us at 1-866-815-0099 or email. info@theautom8group.com.

SOURCE : ledlightinginfo.com | upshine.com | lumoscontrols.com | 1000bulbs.com

What to do with this

Ask for CRI and R9 on every fixture, and ask for the MacAdam step too. If a supplier cannot or will not give them, that is information. Low-cost manufacturers commonly leave these figures off, and they are the figures that decide how a finished room looks.

A specification sheet that leaves out R9 and the MacAdam step is usually leaving them out for a reason.