Monday, 3 October 2011

Dimmable bulbs

I visited Hisashi's bar, Oread, in Tatsuno the other day, and he was saying he wanted to change his lights to LEDs, but had been told it was impossible. He puts on live music in his bar and would like to use LEDs for his stage lights, and adjust them with the row of dimmer switches.

So, if all you need to do to dim an LED is change the current, then why would any LED NOT be dimmable?

The problem is that whenever an LED is packaged into a bulb or fitting, some electronics are added. This is essential to put a cap on the current or voltage and stop a melt down. So the question is whether the bulb has a one-size only approach, and will only send a specific current through the LEDs, or whether it has a cap, and will allow any current to go through, as long as it is no more than the limit.

If the electronics will only send the designated current, then all bets are off regarding dimming. If there is not enough power going into the light, the required voltage will not be reached and no current will flow. LEDs may not obey Ohm's law, but they do obey P = V I. The power will always be the product of the voltage and current. This is sometimes erroneously referred to as Watt's law, but Watt actually had nothing to do with electricity, and the unit we use for electricity was given his name posthumously. P = V I is actually a Joule's law, or a combination of P = I2 R with Ohm's law, V = I R. Back to the LEDs with fixed current internal power supplies, either there will be enough power, and the voltage will be high enough for the full current to flow, or there will not be enough, and no voltage will flow. However fancy the dimmer circuitry on the outside is, dimming won't happen.

If, on the other hand, the electronics put a limit on the current and will only allow current to flow below the meltdown level, then we're in with a chance.

Anyway, there are plenty of dimmable LEDs, in the sense of dimming with a conventional dimmer. Here's one from the US:

I'm only really looking at MR16 GU5.3 bulbs at the moment. These are low-voltage halogen types that I need for the tension wire system.

I got some E17 bulbs for around eight or nine hundred yen to play around with and try out in various appliances we already have. On the bulb instructions, it said we should not, under any circumstances, use the bulb in a fitting with a dimmer, so we tried it in a desk light with a dimmer. Nothing really exciting happened.

As we turned the switch up, first of all, nothing at all happened. Then the light came on, flickering very quickly, almost too quickly to notice, a little below full brightness, then it flashed in one pattern, then flashed in another fashion, then came on at full brightness. What seemed to be happening is that the dimmer on the desk light was interfering with the circuit inside the bulb.

Sharp have a regular lightbulb-like LED, left, which will apparently change brightness.

This site from KC Lightech  also boasts dimming LEDs, in GU5.3. It looks like Cree LEDs inside. They recommend a Panasonic power supply. I wasn't sure how I could actually buy them so I called. They have no stock and will ship an order of a hundred. I only want six!


There is a Philips light here for 6,384 yen a throw, 10W, which can dim, depending on the power supply. They don't always work, but do with Maxray, Daiko, Endo and Koizumi.

This 5.5 W light from Decolight is only 1,200 yen. although it doesn't mention which power supplies it will work with, and careful inspection reveals that it is 100 volts AC. And I thought MR16 GU5.3 was a 12 volt DV size.