LED and Grain of Wheat bulbs

"Robert Wilson" wrote

Hi folks, I have been thinking about the difference between LEDs, and Grain of Wheat bulbs. I myself can tell the difference in the type light they produce. I prefer to use Grain of Wheats for headcodes and headlights, as they use Tungsten lamps at 300mm/ft scale. I acknowledge that more recent lights on trains are LED's, but i'm stuck in the 1980/90's.

Anyone else thinking like me?

Cheers, Rob.

Rob, The one thing to consider is that LED's have a far greater life span than a GOW bulb and smaller power drain, although I do accept I think it would be easier to replace a GOW than an LED should either blow.

I think I prefer LED for loco (due to size) and can accept the difference in lights, but bulbs still look better for street lighting etc.

Can you dim an LED ?

Yes. A typical red LED is operated at a current of 20mA [1] but there's a linear relationship between current and luminous intensity. Double the current and the intensity doubles, etc. How the human eye perceives that is another matter.

Alternatively, and more practically, you modulate the drive to the LED which is how decoders with dimming functions do it.

[1] The data sheet I'm looking at specifies a continuous absolute maximum of 30mA at room temperature or a pulse maximum of 160mA for a 0.1ms pulse with an off time of 0.9ms. This is the basis of LED bicycle lights which pulse the LEDs at a high current. The eye fills in the gaps and perceives a much brighter light (apart form those which have an obviously slow flash rate).

Andrew Crosland

Bear in mind is that LEDs are almost always designed to beam their light output in one direction only, whereas a GOW bulb will provide light in all directions. - hence , as Andy states, GOW will be more effetcive for street lighting & suchlike.

Yes you can, but you won't get the same effect as dimming a GOW bulb. Two ways to dim a LED is to increase the series resistor thus limiting the amount of current and thus the brightness. The other is by sending a pulse width modulated signal, which requires additional circuitry and IMO never looks right as you can often detect the flicker.

I have a few old gas street lamps on our N scale layout, modified to light up via fibre optics. When I used an ultra-bright white LED the lamps looked good, but not right, the light was too white. I then replaced the LED with a 24v bulb (21W run from 12v DC) and the resulting glow from the lamps looked a lot, lot better and gave the layout more character.

Malcolm

A brush with a yellow highlighter pen can help. You can also now buy "golden" or "sunny" white LEDs.

White LEDs often look too "blue" or cold as they are actually blue LEDs with a phosphor layer which emits white light when excited by the blue from the LED chip.

Andrew

wrote

Andrew, I'll bow to your superiour knowledge here ! But I guess this may have some impact on the question I e-mailed you off list ?

Andy

I won't see that until I get home tonight.

Andrew

I prefer LEDs because of a) practically indefinite life; b) very low power drain, whose principal advantage is very cool operation. A secondary advantag e is that in some applications it's feasible to use a small battery to power the LED. Generally, GOW bulb consume 10 to 100x as much power, some even more. NB that it's wattage that counts, not current alone. Eg, an LED at 1.5V and 30mA consumes 0.045watts. A GOW at

12V and 300mA consumes 4 watts.

Some other points other posters have not mentioned:

-- LEDs are packaged in clear plastic, which is sometimes coloured to modify the light. Depending on design and envisioned end use, the chip itself may be very small, around 1mm in diameter or less. You can cut away some of the plastic packaging to make the LED fit odd locations. You can modify the output colour with clear paints made for plastic (those dyes offered for plastic "stained glass" will do nicely.)

-- If you roughen the plastic package with fine sandpaper, the LED will disperse its light in all directions, and do nicely as a streetlamp, etc.

-- You can use micro-plugs, as used on circuit boards, to make LEDs easily replaceable.

-- LEDs are now in the same price range as GOW, especially if bought in bulk. (Many people don't seem to realise that for electronic parts packaged in single and small quantities, the packaging costs more than the part(s), and the warehousing/inventory/sales-tracking overhead may cost as much again.)

HTH

I've settled on using Golden White LEDs for Head and marker lights, they are available in the same sizes as standard LEDs and produce a very tungsten like light.

I model in N and have used the SMT LEDs from Richmond controls with great success, I had in the past taken a standard 3mm LED, put it in a slow speed mini-drill and held a file on the end to produce a sort of T shaped LED which can be mounted behind a headlamp moulding with a suitable hole drilled through it. The SMT LEDs and a short length of Fibre optic are a little quicker to make and install.

Ian

I see Richmond controls now produce ready turned LEDS, see

and they shouldn't get hot - like gow bulbs. I have in the past had the insides of windows and headcodes warped by the bulb mounted (factory) too close to the front bit. Extended use OK, but I don't want a model damaged because I use it.

know about Goden white LEDs. I shall investigate those. I agree with all other correspondents that LED's are better. This is especially true with these Golden white devices.

Thanks for the info.

Regards to all,

Rob.