Thanks for the clarification. After doing some searching I realized I
wasn't going to find an led replacement for the standard 6v15w projector
bulb that is used in the leitz stand.
So far, the only led light I have used with my microscope is the 13 watt
dimmable led bulb (800 lumens) in my swing arm desk lamp placed a few
inches form the standard convex microscope mirror that fits under the
This light is fine for brightfield, but doesn't generate enough light for
darkfield using a 40x or 45x objective. So today I purchased a 26 watt led
narrow beam (25 degrees) dimmable spotlight to fit into my desk lamp. This
bulb is rated at 1500 lumens and has a warm white light with a color rating
of 82CRI and 3000K light. The bulb cost a whopping $70, but If it works for
darkfield and lives up to it's advertised 25,000 hour lifespan it may be
the last microscope bulb I ever need to buy.
My other two sources of light, which work equally well for darkfield are a
fiber optic wand light source, powered by a 21v 150w halogen bulb with a
built in reflector, and the standard 6v 15W incandescent microscope
projector lamp bulb. Both put out about 200 lumens, both cost about $10
each, but are only rated for 200 hours of life.
On Sun, Mar 31, 2013 at 3:18 PM, Chris Albertson
> I think "lumen" is the total amount of light from a bulb. If you add a
> reflector then the reflected light is added to the light that comes
> straight from the bulb. So your projector bulb is "brighter" even if it
> has the same number of lumens. Basically the reflector adds "gain" and
> has a multiplier effect. This effect can be really large as in car
> There are three ways to measure brightness and they all have similar names.
> (1) the total energy from a light bulb, (2) the amount of light per solid
> area in a given direction and (2) light per square meter that hits a
> surface. Confusion happens the names of the units are so similar.
> Yes, there are LED projector bulbs. Some video projects use LEDs, so look
> into replacement parts for those projectors
> I'm still not likley the spectra of LEDs. Try this: In a dark room
> reflect the LED off a refraction grating (a DVD disc makes a decent
> grating) and yu can see the "rainbow" image of the LED on the wall. Many
> of the LEDs I have make bands, not rainbows. Then I confirm by using
> halogen bult and see the expected broad spectra.
> A poor-man's spectroscope is not hard to make. use a DVD for a grating and
> make a 4mm slit and place an SLR camera in back of the slit and watch the
> camera's light meter as you move the DVD. The LEDs I've seen are so
> "spiky" you can see it even in this high school level science experiment.
> Using something this simple you can see the difference between lamps with
> decent and with poor CRI. But it is not good enough to distinguish more
> than just good from poor.
> With LEDs it is a trade off, the most light per watt comes from the
> tri-color LEDs. From a flat sprectra they need phosphors inside the LED
> and a filter to attenuate the peaks. This kills the light per watt
> number. So they compromise and the best or those small surface mount parts
> that look yellow.
> On Sun, Mar 31, 2013 at 11:26 AM, Bob Spez <bobspez@...> wrote:
> > **
> > I've been following this post with some interest but have more questions
> > than answers. The whole subject of specs on lumens is a tricky one. Specs
> > on different websites vary widely. The three types of lighting I use with
> > my Leitz Laborlux black enamel bino scope is the original 6V15W
> > incandescent projector bulb in the base of the Leitz stand. The second
> > of lighting is a 13 Watt LED bulb in a swing arm desk lamp, pointed at a
> > convex microscope mirror under the condenser. The third type is a fiber
> > optic wand powered by a 50 watt halogen bulb. I have placed the wand tip
> > in the same spot as the incandescent projection bulb, under the stand, or
> > directly under the condenser, with very similar results.
> > While all three lighting methods give similar results in Brightfield, but
> > only the incandescent light and the 50 watt halogen fiber optic light
> > achieve a usable darkfield, and they give similar results in lighting
> > (though not in color).
> > Because the 6V15W incandescent bulb is a projection type bulb, it
> > much more brilliance than the lumens would predict.
> > It seems like the type of bulb is more important than the lumens it is
> > rated at. I wonder if they make an LED projection bulb?
> > Bob
> > [Non-text portions of this message have been removed]
> Chris Albertson
> Redondo Beach, California
> [Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]