While there are other articles about bathroom vanity lighting or makeup lighting, they generally tell you what to look for and don't clearly explain why. We thought we'd try to tackle "why" for you before we suggest what to look for. This should help you choose lights that will help you to look your best!
So here are a few things to understand when you choose the lights for your vanity:
Wavelengths & Color
So let's just take an example: a blade of grass might largely reflect green wavelengths of a light source while absorbing most of the other colors present in that light. In this case, we see the green. But think about this: if there aren't any green wavelengths in the light source, can green be reflected? (Answer: no. :)
So the more wavelengths (what we see as "color") present in a light source, the more colors can be reflected back to us. That means the quality of light has everything to do with how well we see colors!
This is why grass appears green in the sunlight (the ultimate in high quality lighting!) but more gray in moonlight. Sunlight contains a full spectrum of wavelengths to reflect, allowing all colors to show. Moonlight does not.
So with makeup, the same idea applies. Your makeup will look different under different lights because those lights might or might not have the right wavelengths to show the true colors of your makeup. And the more similar your bathroom lighting is to the lighting in the places you spend time, the more people will see your makeup the way you meant it to be seen. (The way you saw it in the mirror under your vanity lighting.)
Of course you can't predict all the places you'll be seen and what lights will be used. So to keep things simple, your goal for bathroom lighting should be to provide you with the most accurate representation of colors. And that brings us to CRI.
CRI & Color
CRI, which stands for Color Rendering Index, is currently the best measure of this. It's not a perfect system and will probably be updated before long. But it is an estimate of how accurately a light bulb will make colors appear.
On the traditional CRI scale, incandescent and halogen bulbs score around 100, which is a perfect score. LEDs typically score around 80, though some are available with scores over 90. So you might immediately think that incandescent and halogen bulbs are the best option, but again the CRI score isn't perfect, and some wavelengths may be more present in LEDs than in incandescent and halogen bulbs.
That means some colors might appear more accurately under LED lighting while others might appear more accurately under incandescent or halogen lighting. Take a look at these two images and see which light you prefer for color rendering:
Again, the general goal is to use lights with lots of wavelengths of color in them, but you won't normally have a chart showing you all the wavelengths available from a light bulb. So a general rule of thumb is to stick with light bulbs that have a high CRI.
Even then, remember that an LED might render some colors better than an incandescent bulb (though every LED is unique), so there is an element of personal preference here.
Which should you choose?
Remember that the closer your vanity lights mimic the lights you'll be seen in when you leave your home, the more your makeup will look like it did in the vanity mirror. So if you're most often in an office setting with cool white fluorescent lights, you might want to choose cooler lights for your bathroom vanity. (These will often be around 3500K or 4100K, as color temperatures are measured in "K" or "kelvin.")
If you're outdoors a lot, the sun during the day is considered to have a cool color temperature as well. (It can be rated at 6500K, which appears almost cold / blue in indoor lighting.)
But during sunrise and sunset, and in indoor settings lit by incandescent bulbs (or their replacements), color temperatures are quite warm. (Around 2700K to 3000K.)
Based on this information, you may find that a warmer or cooler bulb color will best suit your everyday needs. But if you're looking for a happy medium, you may want to choose a bulb with around a 3500K color temperature.
Incandescent bulbs and halogen bulbs easily dim on all available dimmer switches, but if you upgrade to LED lighting, be aware of two things:
1) Most but not all LED bulbs can dim. Make sure to check the packaging.
2) You need an LED compatible dimmer. While a dimming LED may work on older dimmers, it's possible you'll get some buzzing, flickering, or simply not enough dimming to get the effect you're after.
LED dimmers are designed to work with this modern technology, and will still work with incandescent and halogen lights as well. So if you're looking for the best in vanity lighting, consider adding dimmers to the mix.
Position of the Lighting
If your vanity doesn't have built in light sockets, consider installing light sconces alongside your mirror; linear lights alongside or above the mirror; or another lighting fixture above the mirror. This will keep you from applying makeup in poor lighting and shadows.
We hope this helps you to figure out the right lights for your needs. Think it through and set them up once and those vanity lights should serve you (and your makeup!) for many years to come.