My wife does found-object assemblages. Many of them are, to give a quick description, box-like dioramas. She has been using low-wattage 120V bulbs to illuminate them (say, in the 7-15W range).
Now, one of the gallery owners she works with suggested that these assemblages might be more salable if the lights were battery-powered, so that the power cord was eliminated, and so that people didn’t have to worry about there being a plug near where they wanted to display the artwork.
And, thought my wife, that seemed like a pretty good idea. The only problem is that even a 7-15W power drain would deplete a battery pretty quickly.
So, the question is: has anyone used low-power light sources? White LEDs come to mind, but I’ve never used them. Any other alternatives? What voltage is required? How many amps do they draw? What about cost? And how do they compare, both objectively and subjectively, to 120V incandescents?
White LEDs are a good solution for low-power small-scale lighting. Typically, they have a V[sub]F[/sub] of around 5 V and draw typically 10-20 mA each. Depending on quantities, they aren’t even terribly expensive anymore. The only real drawback, IMO, is the color. The white LEDs I’ve worked with invariably emit light with a rather harsh bluish cast, so some allowances would need to be made for that.
If the diorama is the scene of a disaffected employee’s emotional beatdown at his annual performance review, and the scene requires the harsh fluorescent lighting of a modern office building, white LEDs with their bluish white cast are perfect.
The light sources I would consider are:
[ul]
[li]Halogen bulbs. These are a little more efficient than regular incandescnet bulbs. My WAG is that a 3-W bulb with a high-quality reflector can be as bright as a bare 7-W incandescent bulb. A 3-W halogen bulb running on four AA batteries should last about 3 hours. Color is nice and warm, but unless you use a regulator circuit, the color gets more red as the battery dies down.[/li][li]LED. More efficient than halogens. As mentioned above, color is usually bluish, and color tends to be inconsistent. I believe the brightest LED readily available is the Luxeon 5W, but these are pretty expensive - I don’t know the unit cost but a flashlight using this bulb usually costs over $100. Luxeon also makes 3W and 1W versions. An LED slowly gets dimmer as the battery is depleted, but the color does not change. Because it gets continuously dimmer it’s hard to define battery life, but flashlights with a 1-W LED and four AA batteries usually claim 30-40 hours of battery life.[/li][li]Fluorescent bulbs. Small ones like those used on battery powered lanterns. These are very efficient (even better than LED, I believe) but the physical size is large, so it can’t be focused. If you need a focused beam and/or sharp shadows, this won’t work. Also the color is a bit harsh.[/li][/ul]
My personal opinion is that battery power is inappropriate for this application. If you really need it as a marketing gimmick, I’d use halogen bulbs and include an AC adapter. The customer can choose between the inconveneince of having a wire and the inconvenience of replacing the batteries every few hours.
I believe you’re correct. From what I’ve read, if you want white light then fluorescent bulbs are most efficient, followed by white LEDs, followed by incandescent. If you want monochrome light at a certain wavelength (red, yellow, etc.) then LEDs are most efficient, followed by fluorescent w/ filter, followed by incandescent w/ filter.
As an LED hobbiest, I can tell you that white LEDs are great for display projects. The only bad thing about them is their somewhat finicky power requirements.
For maximum brightness tempered with lifetime requirements, I’d run most Nichia style whites at between 25-30mA each. For the batch I have, this is the current at 3.7 volts. The hard part of powering LEDs is finding a low voltage 4.0-1.6v (depending on the chemistry/color) supply.
I’ve been using LM317 adjustable regulators. Here are some schematics. All you need is a potentiometer and a resistor. To keep the heat down, use a low voltage dc wall wart to power the 317. These are available at Radio Shack.
Luxeons are nice, too. For display/diorama lighting, I’d probably go with several 5mm Nichias to get more angles. The Luxeons get more than a little hot, too!
