Using LEDs for lighting figures or models ?

With flexible strips of LEDs becoming ever more affordable and easier available it might be tempting to use these strips for illuminating the shelves of a display cabinet: just stick a strip of LEDs to the lower front edge of a shelf to light the space below.
These strips come with either single color LEDs (of which 'white' is most useful for lighting purposes) or multi-color (RGB) LEDs .

Here are some reasons against using these LEDs as 'permanent' lighting for figure, doll or plastic scale model displays.

Affordable multi-color LEDs (made up of tiny Red, Green and Blue LED elements) can not emit white light.
The light may look white-ish to the eye but a lot of colors are simply missing from the light (as compared to the continuous 'rainbow' of colors emitted by an incandescent lamp) so many colors including the skin tones and clothes of your figures will look odd. More expensive multi-color LEDs (made up of tiny Red, Green, Blue and Amber LED elements) will do a slightly better job but there are still too many colors missing to look convincing.
Almost all affordable 'white' LEDs emit UV light, which is harmful to vinyl, polystyrene and cured CA glue.
Most of the UV light is converted into white light by a layer of phosphor particles inside the LED (just as with a fluorescent lamp), but sufficient UV light will pass through the phosphor layer to be harmful to vinyl at distances smaller than about 40cm (16in).
The phosphor layer inside the LEDs will age faster than the actual LED does, so UV emissions will increase over time.
Although the resulting 'white' light contains a broader range of colors than the light from RGB LEDs the light is not truly white, there is usually a greenish or yellowish cast.
The clear flexible strips containing the LEDs emit plasticisers that may cause vinyl, pleather and polystyrene to deteriorate.
Straight from the package these strips emit a really strong smell which is a first indication that the strips should not be used in confined spaces such as display cabinets. The clear strips get warmed up slightly when the LEDs inside are lit, causing yet more plasticisers to be emitted.

The 'white' light of the RGB LEDs contains a much larger amount of blue than is perceived by the eye (the human eye is less sensitive to blue) so what looks close-to-white to the eye looks predominantly blue to a digicam (even with the white balance of the camera adjusted).
The picture on the left shows the same RGB LED strip as the picture at the top of the page, emitting the same 'white' light. All I did was put a dolls head next to the strip and switch off the ambient lighting.

The limited color range of the RGB LEDs and the use of UV light in most 'white' LEDs were a bit of a disappointment to me, I hope this page will keep you from trying LEDs for lighting figure or model displays and getting disappointed as well

Types of white LEDs

There are two types of 'white' LEDs:
The first type is mostly used in ambient lighting and emits bright yellowish to greenish 'warm white' light.
The second type is used in flashlights, this type emits a bright blueish-white light.
The blueish types rarely emit any UV light but are much more expensive, are not as bright as the 'warm white' types and as with RGB LEDs its white light only consists of a limited set of colors.
There are types of 'white' LEDs with a more true white color and there are types that use blue instead of UV light to illuminate the phosphor layer, however those are much more expensive and are rarely used for flexible lighting strips.

	UV-based white LEDs contain an opaque layer of phosphor (usually yellow or greenish white) between the lens at the top and the metallic parts inside
	True 'white' LEDs have a transparent or translucent package, leaving the shiny metallic parts of the LED visible

Improved RGB LED strips

A year later most of the reservations I mentioned above still stand (most white LEDs emit UV, the flexible strips do emit plasticisers) but I recently bought a strip of multi-color LEDs (made up of tiny Red, Green and Blue LED elements) that do a pretty decent job of emitting white light:

new RGB LED strip set to white light To both the naked eye and my digicam the emitted light looks bright white with a decent color spectrum.
The only downside I noticed is that the blue LEDs in these strips also emit some UV (like black-light: anything fluorescent will light up brightly).

These new flexible RGB LED strips are much brighter than the ones I bought last year and come with a remote controller with much more options, yet the set costs about 2/3rds of the price I paid for last years set.

new RGB LED strip packaging The picture shows the light at maximum brightness, it can be dimmed in 9 steps of 10% .
At maximum brightness this 5mtr long strip is rated at 16.5 Watts with a yield of 850 Lumen (that's equivalent to a 60 Watts incandescent bulb).
Apart from white light the controller included in the set allows the LEDs to emit a broad choice of colors.

Easiest way to tell the new sets apart from the older ones is by the larger remote controller, the old remote has 24 buttons, the new one has 44 buttons.

While I still would recommend against fitting these strips inside a closed display cabinet because of the UV emitted by the blue LEDs and the risk of the strips emitting plasticisers, the light of these new multi-color RGB LED strips does look suitable for illuminating scale models or figures.

LED strips over desk I mounted both the white and RGB strips I bought on a piece of plywood and fitted that to the ceiling over my desk, resulting in a versatile light source that can be dimmed and adjusted for color.
However when using the RGB strips for lighting my desk I turn the blue LEDs off as the intensity of the blue light combined with the emitted UV light may cause eye damage (see link to report from French ANSES Institute for Health and Safety below).

In the meantime I did notice that even the combined 'warm white' and RGB light is lacking too many colors to be useful for photographing completed models and figures, in particular red values are lacking which makes skin tones look odd.
A measure for color rendering is the Color Rendering Index where pure sunlight has the maximum value of 100. A higher CRI value means better color rendering. An average Fluorescent Tube has a CRI value of about 80, color photography requires a CRI value of at least 90.
Apart from CRI the color temperature of white light is also relevant. A low color temperature value (2000-3000°K) indicates yellowish light and a high value (in excess of 6000°K) indicates blueish light. Average daylight has a color temperature of about 6500°K.
With LED strips there are usually no values for color rendering or color temperature supplied, LED bulbs usually do have these values listed.
A digital camera can compensate for a different color temperature by adjusting the 'White Balance' setting, but there's no compensating for a light source with a low CRI.

Determining safe distance

To help with determining a safe distance and position between UV radiating LEDs and subject:

most LEDs emit light in a cone spanning about 120 degrees;
at 30cm (12in) distance from a UV-emitting white LED the amount of UV emitted is about the same as bright daylight (not direct sunlight);
at 30cm distance the amount of UV per square mm is about 1% of what is emitted directly in front of the LED.

I prefer to keep at least 50cm (20in) distance between LEDs and subject, however I do not use LEDs as a permanent light source for lighting scale models or figures.
In all cases the UV light emitted by LEDs is UV-A of long wavelength (380-395nm) so not as harmful as UV from direct sunlight.

Sources

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