Light Bulbs

When the first commercially popular light bulbs came out, they contained a carbon filament that emitted light by being heated with electricity passing through them, and the glass bulb had the air removed to prevent the carbon filament from burning up. As time went on, improvements came out, such as tungsten filaments and halogen fill to improve their efficiency, and colored and shaped glass to change the appearance of the bulb and light. However, demands for more efficient lighting led to the adoption of fluorescent bulbs, followed by light emitting diodes (LEDs) once technology improved. With the advancement of technology, the rudimentary way of sizing bulbs by their wattage no longer worked, and the quality of light became more of an option. Now, with all of the new measurements combined with stretched marketing, it can be confusing to shop for light bulbs, but all the new metrics can give you greater control of the look and feel of your space once you know how to navigate them.

Lumens

Lumens is the objective measurement of light output of the light bulb, as a function of the output over the area it shines on. While some manufacturers may claim their bulb’s equivalent to a high wattage incandescent, the truth lies in the lumens: the more lumens a bulb produces, the brighter. 100 watt incandescent bulbs generally produce around 1100 lumens, and LED bulbs can easily exceed this output with far lower energy usage. There are even high brightness bulbs that can fill a room with light, but be aware that high brightness bulbs often can’t be used in an enclosed fixture. Check the packaging to see if the bulb can be used in an enclosed fixture when getting high brightness bulbs.

Color Temperature (K)

Another measurement that’s popped up is color temperature. Color temperature refers to the light emission of an ideal black body at the temperature measured in Kelvin. Imagine heating a piece of metal: as the metal gets hotter, it starts glowing from red to orange, to white, to theoretically blue and beyond. The temperature of the piece that matches a source of light is the color temperature. Sunrise is around 1750 K, and bright day sky is somewhere around 15000 K to 27000 K. Incandescent bulbs are generally around 2700 K. Lower color temperature is said to ‘feel’ warmer, while higher color temperature may give a cooler, cleaner look, or even start to mimic daylight, however some people may find high color temperature sterile. A good compromise is 3000 K, giving a warm but clean look. Some bulbs also offer a way to change the color temperature. There are even some that mimic sunset to help leverage your circadian rhythm. Matching color temperature in a room is important to get a unified look: mismatched light gives an unusual appearance that may not be appealing. Keep in mind the color temperature of the bulbs in your room already when swapping lights to avoid this.

Color Rendering Index

The most underappreciated aspect of light bulbs is their color rendering index (CRI), or the ability to emit the full spectrum of light. The human eye can be tricked into thinking a source of light is white by simply mixing a couple wavelengths of light. These hit the rods and cones of the eye, and send feedback that all of the colors are being seen. However, the resulting light can give objects an unusual appearance, as the light is only made of a few wavelengths of light, and may not bounce and be absorbed correctly by objects. Conversely, black body emitters are objects that emit a continuous spectrum of electromagnetic radiation with the distribution of the radiation being based on the temperature. Just as described before, the hotter the black body emitter, the bluer the light coming from it appears. The sun is one such black body emitter, being a heated ball of plasma. Sunlight has a CRI of 100, and covers the whole visible spectrum. Similarly, because they use a heated piece of wire which also makes them black body emitters, incandescent bulbs also have a CRI of 100. ‘White’ LEDs actually play a trick, and are usually a blue, violet, or ultraviolet LED with phosphor that absorbs some of the emitted light, and emits another color of light. The mix of phosphors can change the balance of light emitted, changing the color temperature as well as the color rendering index by adding more wavelengths of light. Early fluorescent bulbs, which also use phosphors to produce white light, were limited in the wavelengths they could emit, leading to the ‘hospital’ look and feel of fluorescent bulbs, with a cold color temperature and very poor color rendering index. As time went on, fluorescent bulbs improved their phosphor mix, and had better CRIs. Early high brightness white LEDs struggled with a different issue: the heat generated by the LEDs as well as the high drive energy would cause the phosphors to decay and the bulb would slowly fade to blue. Even now, you can occasionally find street lights and news stories of street lights that have turned purple because the phosphors on those LEDs has failed. While we now have cooler running LEDs and more robust phosphors, LED manufacturers have started to backpedal, and your typical LED bulb is no longer a high-CRI bulb. Instead, manufacturers found that around 80 CRI is an acceptable compromise between cost and appearance. However, specific high-CRI bulbs exist, and the quality of light from these bulbs is better than lower CRI bulbs. Not every bulb in your home needs to be a high CRI bulb, though: outdoor lights, lights in a cupboard or closet, and other places may not really benefit from a high CRI bulb. However, choosing to put them in places you tend to occupy or in workspaces may make the space feel better. You can try a similar effect for free by comparing a space with sunlight and artificial light, and seeing if you prefer the difference. High CRI has also been linked to helping with mood such as seasonal affective disorder, since it mimics a more natural spectrum of light.

Dimmable Bulbs

One caveat with LEDs is with dimmers: not all bulbs are dimmable, and not all dimmers will work even with dimmable bulbs. Dimmers often work by chopping up the power and discarding pieces to produce a lower average output. Incandescent bulbs, by way of their function, smooth out the chopped-up pieces, making a dimmer light. LEDs are much faster in their function, and the chopped up pieces can result in visible strobing. Since LEDs can’t be given wall power directly, they are powered with a driver. These drivers are sometimes able to interpret the chopped-up pieces, and modulate the LEDs to dim the light. However, sometimes the dimmer’s output is too aggressive, and the driver in a bulb isn’t able to properly convert the power and drive the LEDs. Drivers also need a minimum amount of power to boot up, so sometimes LEDs need to be brought up to a level before bringing them back down to the desired level. Finally, some bulbs may not have a driver that’s capable of being dimmed. Symptoms of incompatible bulbs and dimmers are blinking, strobing, or no light at all. With that said, some bulbs, like these, also change their color temperature with their brightness to better mimic the warmer glow of dimmed-down incandescent bulbs.

Final Notes

LED bulbs have more ways of controlling the light in your space, and capturing and controlling the mood and feeling you want. Efficiency is still a factor with LEDs, however, so look for bulbs that produce the most lumens for the least actual watts. LED bulbs that use more watts for their lumens are often ‘over-driven’ or pushed outside of the diode manufacturers specification. Manufacturers do this to save on the cost of the bulbs by reducing the number of LEDs in a bulb, and pushing them harder to make up the difference. Over-driven bulbs are not only less efficient, but are also shorter lived: pushing them harder wears them out faster. On the other hand, Dubai mandated more efficient bulbs. Compared to bulbs available elsewhere, ‘Dubai bulbs’ have LEDs that are under-driven to meet the government’s demand, and are stuffed with more diodes to make up the difference in lumens. These bulbs run more efficiently, last longer, and run cooler. Another note with LEDs is the cooler bulbs allow for more aggressive plastic lenses, letting you get highly focused bulbs for dramatic spot lighting. Overall, while more thought needs to be put forward with new bulbs, the capabilities and control over the light they offer far outweigh incandescent.