Visibility of bruises under LED light

I have noticed that if I have a bruise, it shows up much more readily under LED light than any other light. Oddly it seems to show up least readily under direct sunlight.

Since sunlight is presumed to have all visible frequencies, why would any other type of light make it easier to see bruises? I assume this is somehow related to what frequencies are absorbed or scattered by the upper layers of skin or something (which I understand is why veins look blue/green through the skin even though they are actually red).

I have been taking a blood thinner so have more bruises than usual. I have been thinking about this a lot.

Before you overthink this too much, I think you should look at the color temperature of the LEDs that do this and then compare it to an incandescent bulb of the same temperature. It could simply be that different colored lights make different things show up. A cooler (colored) light may show more blue than a warmer light.

If the same thing happens with a 2700k vs a 5000k LED light, but doesn’t happen at all with any incandescent or CFL bulbs, I’d be more inclined to believe it has something, specifically, to do with LEDs.

sunlight (and light from incandescent lamps) is broad spectrum light. LED lights have a “peaky” spectrum; they typically use a high-intensity blue LED as the light source and drop a blob of phosphor on top of it to shift to “white” light.

it’s possible the LED light you’re using has more output in one part of the spectrum to make your bruising more apparent.

ETA: Ninja’d by jz78817!
Buy a better LED bulb—look for those advertised as having a high color rendering index (CRI).

Joey P makes a great point. To expand on it a bit, you might consider not just the labeled color temperature (e.g., 2700K) but also the emitted spectrum of the bulb in question.
(Note: the plots in the link are objectively terrible—axes lack units and scale or are unlabeled altogether. They’re OK on a qualitative level, though).

The OP notes correctly that the sun’s emission spectrum includes almost all of the colors humans can see, which only makes sense—humans evolved on an earth lit by sunlight. The sun’s emitted spectrum is broad (to humans) and mostly continuous. Sunlight’s intensity peaks somewhere between yellow and green, but it slopes down fairly smoothly on either side as you get closer to red and blue, respectively.

But lightbulbs are different. Both LEDs and fluorescent bulbs tend to have much spikier emissions spectra than the sun or incandescent bulbs. Their intensity isn’t smoothly distributed across the color spectrum, but rather made up of several peaks—a 2700K CFL typically has a big, narrow red peak, a few biggish-and-narrow yellow and green peaks, and a smaller-but-narrow blue peak.

That’s a big part of why replacing so many people were disappointed with early CFLs: the light quality from a 2700K CFL is terrible compared to the light from an incandescent bulb of the same color temperature. In isolation, our brains make the light both look white, but when both bulbs are lit in the same room at the same time, the difference in light quality is hard to miss.

Because LEDs tend to have a tall, narrow intensity spike in the blue range and not very much intensity in the red range, people whose veins and bruises look blue in sunlight can expect to see that effect magnified under an LED.

Because our brains tend to adjust the colors we perceive on the fly, the bluer LED-lit veins don’t look a lot bluer—but they do have more contrast against white skin, as would bruises. Since contrast tends to catch the human eye, I suspect that explains why your bruises are more noticeable under an LED.

The CRI of LEDs has come a long way in the past decade or two, and high-CRI LEDs are are significantly better than modern-but-pedestrian models. If you decide to try a high-CRI LED, I’d love to know whether your bruises are less visible than under your existing LEDs.

Yes, but it also includes colors we can’t see, a topic for another thread.

I had not heard of this before, and do not know if CRI typically appears on LED labels. The ones I have noticed this on most are a built-in one in my shower ceiling, so no way to find out the CRI, and the ones in my office men’s room, ditto. I will investigate further, time permitting.

You could pull the bulbs and Google any identifying text.

But AIUI high-CRI bulbs are still a specialty item and priced accordingly. If you bought a high-CRI LED, you’d probably know it.

When I say built-in, I mean that they are integrated fixtures. I would have to dismantle them to get at the bulb. My bathroom light is just an off-the-shelf Home Depot item, so probably not high-CRI.